1.
PDP-11 architecture
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The PDP-11 architecture is an instruction set architecture developed by Digital Equipment Corporation. It is implemented by central processing units and microprocessors used in PDP-11 minicomputers and it was in wide use during the 1970s, but was eventually replaced by the more powerful VAX-11 architecture in the 1980s. Thirty-two-bit data—supported as extensions to the architecture, e. g. The PDP-11s 16-bit addresses can address 64 KB, the basic logical address space is 32K words, but the high 4K are not populated because input/output registers on the bus responded to addresses in that range. So originally, a fully loaded PDP-11 had 28K words, the processor reserves low memory addresses for two-word vectors that give a program counter and processor status word with which to begin a service routine. When an I/O device interrupts a program, it places the address of its vector on the bus to indicate which service routine should take control, the lowest vectors are service routines to handle various types of trap. The article PDP-11 describes how the 16-bit logical address space became an insurmountable limitation, during the life of the PDP-11, the following techniques were used to work around the limitation, Later-model PDP-11 processors included memory management to support virtual addressing. The physical address space was extended to 18 or 22 bits, the logical address space remained limited to 16 bits. Some models, beginning with the PDP-11/45, can be set to use 32K words as the space for program code. Some operating systems—notably Unix since edition V7, and RSX11-M+—rely on this feature, Programming techniques, such as overlaying a block of stored instructions or data with another as needed, can conceal paging issues from the application programmer. For example, the Modula-2 compiler produces code under which the run-time system swaps 8 Kb pages into memory as individual procedures receive control, the CPU contains eight general-purpose 16-bit registers. Register R7 is the program counter, although any register can be used as a stack pointer, R6 is the stack pointer used for hardware interrupts and traps. Most instructions allocate six bits to specify an operand, three bits select one of eight addressing modes, and three bits select one of the eight general registers. The use of three-bit groups makes octal notation natural, in the following sections, each item includes an example of how the operand would be written in assembly language for a prototypical single-operand instruction with symbol OPR. Rn means one of the registers, written R0 through R7, signifies the contents of that register. The following eight modes can be applied to any general register and their effects when applied to R6 and R7 are set out separately in the following sections. In index and index deferred modes, X is a 16-bit value taken from a word of the instruction. In double-operand instructions, both operands can use these modes, such instructions are three words long
2.
DECtape
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DECtape was a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DECs 32-bit systems, VAX/VMS support for it was implemented, DECtapes were 3/4 inch wide, and formatted into blocks of data that could each be read or written individually. Each tape stored 184K 12-bit PDP-8 words or 144K 18-bit words, block size was 128 12-bit words, or 256 18-bit words for the other machines. From a programming point of view, DECtape behaved like a very slow disk drive, DECtape had its origin in the LINCtape tape system, which was originally designed by Wesley Clark at the MIT Lincoln Laboratory as an integral part of the LINC computer. There were simple LINC instructions for reading and writing tape blocks using a machine instruction. The design of the LINC, including LINCtape, was placed in the domain because its development had been funded by the government. LINCtape drives were manufactured by companies, including Digital. In turn, LINCtapes origin can be found in the magnetic tape system for the historic Lincoln Laboratory TX-2 computer, designed by Richard L. The TX-2 Tape System is the ancestor of LINCtape, including the use of two redundant sets of five tracks and a direct drive tape transport, but it used a physically incompatible tape format. Digital initially introduced the Type 550 Microtape Control and Type 555 Dual Microtape Transport as peripherals for the PDP-1 and PDP-4 computers, the initial specifications for the Type 550 controller discussed a significant advance beyond the LINCtape, the ability to read and write in either direction. By late 1964, the Type 555 transport was being marketed as a DECtape transport, the tape transport used on the LINC was essentially the same as the Type 555 transport, with the same interface signals and the same physical tape medium. The LINC and DEC controllers, however, were incompatible, while LINCtape supported high-speed bidirectional block search, it only supported actual data read and write operations in the forward direction. DECtape used a different mark track format to provide for the possibility of read and write operations in either direction. DEC applied for a patent on the features incorporated into DECtape in late 1964. It is notable that the inventor listed on this patent, Thomas Stockebrand, was also an author of the paper on the TX-2 tape system from which the LINC tape was derived. Eventually, the TC12-F tape controller on the PDP-12 supported both LINCtape and DECtape on the same transport, as with the earlier LINC-8, the PDP-12 was a PDP-8 augmented with hardware support for the LINC instruction set and associated laboratory peripherals. DECtape was designed to be reliable and durable enough to be used as the storage medium for a computers operating system. It was possible, although slow, to use a DECtape drive to run a small OS such as OS/8 or OS/12
3.
Minicomputer
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A minicomputer, or colloquially mini, is a class of smaller computers that developed in the mid-1960s and sold for much less than mainframe and mid-size computers from IBM and its direct competitors. The class formed a group with its own software architectures. Minis were designed for control, instrumentation, human interaction, and communication switching as distinct from calculation, many were sold indirectly to Original Equipment Manufacturers for final end use application. During the two decade lifetime of the class, almost 100 companies formed and only a half dozen remained. They usually took up one or a few 19-inch rack cabinets, the definition of minicomputer is vague with the consequence that there are a number of candidates for the first minicomputer. An early and highly successful minicomputer was Digital Equipment Corporations 12-bit PDP-8, later versions of the PDP-8 took advantage of small-scale integrated circuits. The important precursors of the PDP-8 include the PDP-5, LINC, the TX-0, the TX-2, DEC gave rise to a number of minicomputer companies along Massachusetts Route 128, including Data General, Wang Laboratories, Apollo Computer, and Prime Computer. Minicomputers were also known as midrange computers and they grew to have relatively high processing power and capacity. They were used in manufacturing process control, telephone switching and to control laboratory equipment, in the 1970s, they were the hardware that was used to launch the computer-aided design industry and other similar industries where a smaller dedicated system was needed. The 7400 series of TTL integrated circuits started appearing in minicomputers in the late 1960s, the 74181 arithmetic logic unit was commonly used in the CPU data paths. Each 74181 had a bus width of four bits, hence the popularity of bit-slice architecture, some scientific computers, such as the Nicolet 1080, would use the 7400 series in groups of five ICs for their uncommon twenty bits architecture. Starting in the 1980s, many minicomputers used VLSI circuits, the result was that minicomputers and computer terminals were replaced by networked workstations, file servers and PCs in some installations, beginning in the latter half of the 1980s. Also, the Microsoft Windows series of operating systems, beginning with Windows NT, now included server versions that supported preemptive multitasking, Digital Equipment Corporation was once the leading minicomputer manufacturer, at one time the second-largest computer company after IBM. DEC was sold to Compaq in 1998, while Data General was acquired by EMC Corporation, today only a few proprietary minicomputer architectures survive. The IBM System/38 operating system, which introduced many advanced concepts, realising the importance of the myriad lines of legacy code written, AS stands for Application System. Great efforts were made by IBM to enable programs written for the System/34. The AS/400 was replaced by the iSeries, which was replaced by the System i. In 2008, the System i was replaced by the IBM Power Systems, by contrast, competing proprietary computing architectures from the early 1980s, such as DECs VAX, Wang VS and Hewlett Packards HP3000 have long been discontinued without a compatible upgrade path
4.
Digital Equipment Corporation
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Digital Equipment Corporation, also known as DEC and using the trademark Digital, was a major American company in the computer industry from the 1950s to the 1990s. DEC was a vendor of computer systems, including computers, software. Their PDP and successor VAX products were the most successful of all minicomputers in terms of sales, DEC was acquired in June 1998 by Compaq, in what was at that time the largest merger in the history of the computer industry. At the time, Compaq was focused on the market and had recently purchased several other large vendors. DEC was a major player overseas where Compaq had less presence, however, Compaq had little idea what to do with its acquisitions, and soon found itself in financial difficulty of its own. The company subsequently merged with Hewlett-Packard in May 2002, as of 2007 some of DECs product lines were still produced under the HP name. From 1957 until 1992, DECs headquarters were located in a wool mill in Maynard. DEC was acquired in June 1998 by Compaq, which merged with Hewlett-Packard in May 2002. Some parts of DEC, notably the business and the Hudson. Initially focusing on the end of the computer market allowed DEC to grow without its potential competitors making serious efforts to compete with them. Their PDP series of machines became popular in the 1960s, especially the PDP-8, looking to simplify and update their line, DEC replaced most of their smaller machines with the PDP-11 in 1970, eventually selling over 600,000 units and cementing DECs position in the industry. Originally designed as a follow-on to the PDP-11, DECs VAX-11 series was the first widely used 32-bit minicomputer and these systems were able to compete in many roles with larger mainframe computers, such as the IBM System/370. The VAX was a best-seller, with over 400,000 sold, at its peak, DEC was the second largest employer in Massachusetts, second only to the Massachusetts State Government. The rapid rise of the business microcomputer in the late 1980s, DECs last major attempt to find a space in the rapidly changing market was the DEC Alpha 64-bit RISC instruction set architecture. DEC initially started work on Alpha as a way to re-implement their VAX series, DEC was acquired in June 1998 by Compaq, in what was at that time the largest merger in the history of the computer industry. At the time, Compaq was focused on the market and had recently purchased several other large vendors. DEC was a major player overseas where Compaq had less presence, however, Compaq had little idea what to do with its acquisitions, and soon found itself in financial difficulty of its own. The company subsequently merged with Hewlett-Packard in May 2002, as of 2007 some of DECs product lines were still produced under the HP name
5.
Programmed Data Processor
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Programmed Data Processor was a series of minicomputers made and marketed by the Digital Equipment Corporation from 1957 to 1990. So instead, Digital used their existing line of logic modules to build a Programmed Data Processor, the various PDP machines can generally be grouped into families based on word length. What is believed to be the first video game, Spacewar. was developed for this machine, along with the first known word processing program for a general-purpose computer, pDP-2 A number reserved for an unbuilt, undesigned 24-bit design. PDP-3 First DEC-designed 36-bit machine, though DEC did not offer it as a product, the only PDP-3 was built by the CIAs Scientific Engineering Institute in Waltham, MA to process radar cross section data for the Lockheed A-12 reconnaissance aircraft in 1960. Architecturally it was essentially a PDP-1 controlling a PDP-1 stretched to 36-bit word width, PDP-4 18-bit machine intended to be a slower, cheaper alternative to the PDP-1, it was not considered commercially successful. All later 18-bit PDP machines were based on a similar, but enlarged instruction set, more powerful, one customer of these early PDP machines was Atomic Energy of Canada. The installation at Chalk River, Ontario included an early PDP-4 with a display system, introduced the instruction set later expanded, in the PDP-8, to handle more bit rotations and to increase the maximum memory size from 4K words to 32K words. Very elegant architecture, introduced the set later used in the PDP-10. PDP-7 Replacement for the PDP-4, DECs first wire-wrapped machine, the first version of Unix, and the first version of B, a predecessor of C, were written for this machine at Bell Labs, as was the first version of MUMPS. PDP-8 12-bit machine with an instruction set, DECs first major commercial success. Many were purchased by schools, university departments, and research laboratories, later models were also used in the DECmate word processor and the VT-78 workstation. LINC-8 A hybrid of the LINC and PDP-8 computers, two instruction sets, PDP-9 Successor to the PDP-7, DECs first micro-programmed machine. It featured an increase of approximately twice that of the PDP-7. The PDP-9 was also one of the first small or medium scale computers to have a monitor system based on DIGITALs own small magnetic tape units. The PDP-9 established minicomputers as the edge of the computer industry. PDP-10 36-bit timesharing machine, and fairly successful over several different models, the instruction set was a slightly elaborated form of that of the PDP-6. PDP-11 The archetypal minicomputer, a 16-bit machine and another success for DEC. The LSI-11 was a four-chip PDP-11 used primarily for embedded systems, the 32-bit VAX series was descended from the PDP-11, and early VAX models had a PDP-11 compatibility mode
6.
Instruction set architecture
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An ISA includes a specification of the set of opcodes, and the native commands implemented by a particular processor. An instruction set architecture is distinguished from a microarchitecture, which is the set of design techniques used, in a particular processor. Processors with different microarchitectures can share a common instruction set, for example, the Intel Pentium and the AMD Athlon implement nearly identical versions of the x86 instruction set, but have radically different internal designs. The concept of an architecture, distinct from the design of a machine, was developed by Fred Brooks at IBM during the design phase of System/360. Prior to NPL, the companys computer designers had been free to honor cost objectives not only by selecting technologies, the SPREAD compatibility objective, in contrast, postulated a single architecture for a series of five processors spanning a wide range of cost and performance. In addition, these virtual machines execute less frequently used code paths by interpretation, transmeta implemented the x86 instruction set atop VLIW processors in this fashion. A complex instruction set computer has many specialized instructions, some of which may only be used in practical programs. Theoretically important types are the instruction set computer and the one instruction set computer. Another variation is the very long instruction word where the processor receives many instructions encoded and retrieved in one instruction word, machine language is built up from discrete statements or instructions. Examples of operations common to many instruction sets include, Set a register to a constant value. Copy data from a location to a register, or vice versa. Used to store the contents of a register, result of a computation, often called load and store operations. Read and write data from hardware devices, add, subtract, multiply, or divide the values of two registers, placing the result in a register, possibly setting one or more condition codes in a status register. Increment, decrement in some ISAs, saving operand fetch in trivial cases, perform bitwise operations, e. g. taking the conjunction and disjunction of corresponding bits in a pair of registers, taking the negation of each bit in a register. Floating-point instructions for arithmetic on floating-point numbers, branch to another location in the program and execute instructions there. Conditionally branch to another if a certain condition holds. Call another block of code, while saving the location of the instruction as a point to return to. Load/store data to and from a coprocessor, or exchanging with CPU registers, processors may include complex instructions in their instruction set
7.
Unibus
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The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon Bell and student Harold McFarland while at Carnegie Mellon University, the Unibus consists of 72 signals, usually connected via two 36-way edge connectors on each printed circuit board. When not counting the power and ground lines, it is referred to as a 56-line bus. It can exist within a backplane or on a cable, up to 20 nodes can be connected to a single Unibus segment, additional segments can be connected via a bus repeater. The bus is completely asynchronous, allowing a mixture of fast and it allows the overlapping of arbitration while the current bus master is still performing data transfers. The 18 address lines allow the addressing of a maximum of 256 kiB, typically, the top 8 kiBw is reserved for the registers of the memory-mapped I/O devices used in the PDP-11 architecture. The design deliberately minimizes the amount of redundant logic required in the system, for interrupts, only the interrupt-fielding processor needs to contain the complex timing logic. The end result is that most I/O controllers can be implemented with simple logic, type 1 lines are a normal multi-sender wired-OR bus with pull-up resistors at each end of the bus, typically on a terminator card. Type 2 lines are selectively propagated by each card to the next slot – if the card wants to keep the request grant it will assert the SACK line and not propagate the request to the next slot. If a slot is empty, it is necessary to install a grant continuity card in the slot to propagate the four type 2 signals to the next card, type 3 signals are generated by the power supply and have only a single sender. They warn the devices on the bus when the power is about to fail, so devices can execute an orderly shutdown
8.
Direct memory access
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Direct memory access is a feature of computer systems that allows certain hardware subsystems to access main system memory, independent of the central processing unit. Without DMA, when the CPU is using programmed input/output, it is fully occupied for the entire duration of the read or write operation. This feature is useful at any time that the CPU cannot keep up with the rate of data transfer, many hardware systems use DMA, including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for data transfer in multi-core processors. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without DMA channels, DMA can also be used for memory to memory copying or moving of data within memory. DMA can offload expensive memory operations, such as copies or scatter-gather operations. An implementation example is the I/O Acceleration Technology, Standard DMA, also called third-party DMA, uses a DMA controller. A DMA controller can generate memory addresses and initiate memory read or write cycles and it contains several hardware registers that can be written and read by the CPU. These include an address register, a byte count register. To carry out an input, output or memory-to-memory operation, the host processor initializes the DMA controller with a count of the number of words to transfer, the CPU then sends commands to a peripheral device to initiate transfer of data. The DMA controller then provides addresses and read/write control lines to the system memory, each time a byte of data is ready to be transferred between the peripheral device and memory, the DMA controller increments its internal address register until the full block of data is transferred. In a bus mastering system, also known as a first-party DMA system, where a peripheral can become bus master, it can directly write to system memory without involvement of the CPU, providing memory address and control signals as required. Some measure must be provided to put the processor into a hold condition so that bus contention does not occur, DMA transfers can either occur one byte at a time or all at once in burst mode. In burst mode DMA, the CPU can be put on hold while the DMA transfer occurs, when memory cycles are much faster than processor cycles, an interleaved DMA cycle is possible, where the DMA controller uses memory while the CPU cannot. An entire block of data is transferred in one contiguous sequence, the mode is also called Block Transfer Mode. It is also used to stop unnecessary data, the cycle stealing mode is used in systems in which the CPU should not be disabled for the length of time needed for burst transfer modes. However, in cycle stealing mode, after one byte of data transfer and it is then continually requested again via BR, transferring one byte of data per request, until the entire block of data has been transferred. By continually obtaining and releasing the control of the system bus, the CPU processes an instruction, then the DMA controller transfers one data value, and so on
9.
Peripheral
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A peripheral is an ancillary device used to put information into and get information out of the computer. Touchscreens are an example that combines different devices into a hardware component that can be used both as an input and output device. A peripheral device is defined as any auxiliary device such as a computer mouse or keyboard that connects to. Other examples of peripherals are image scanners, tape drives, microphones, loudspeakers, webcams, common input peripherals include keyboards, computer mice, graphic tablets, touchscreens, barcode readers, image scanners, microphones, webcams, game controllers, light pens, and digital cameras. Common output peripherals include computer displays, printers, projectors, computer hardware Controller Display device Expansion card Punched card input/output Punched tape Video game accessory
10.
PDP-8
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The 12-bit PDP-8, produced by Digital Equipment Corporation, was the first successful commercial minicomputer. DEC introduced it on March 22,1965 priced at $18,500 and eventually more than 50,000 systems. The PDP-8 was the first computer to be sold for under $20,000 and it was the first widely sold computer in the DEC PDP series of computers. The chief engineer who designed the initial version of the PDP-8 was Edson de Castro, the earliest PDP-8 model uses diode–transistor logic, packaged on flip chip cards, and is about the size of a small household refrigerator. This was followed in 1966 by the PDP-8/S, available in desktop, using a one-bit serial arithmetic logic unit implementation, allowed the PDP-8/S to be smaller, less expensive and slower than the original PDP-8. The PDP-8/S was about 20% of the cost and about 10% of the performance of the PDP-8, the only mass storage peripheral available for the PDP-8/S was the DF32 disk. Later systems returned to a faster, fully parallel implementation but use less costly transistor-transistor logic MSI logic. Most surviving PDP-8s are from this era, the PDP-8/E is common, and well-regarded because so many types of I/O devices were available for it. It was often configured as a general-purpose computer, the last commercial PDP-8 models introduced in 1979 were called CMOS-8s. They use custom complementary metal-oxide-semiconductor microprocessors and they were not priced competitively, and the offering failed. The IBM PC in 1981 cemented the doom of the CMOS-8s by making a legitimate, Intersil sold the integrated circuits commercially through to 1982 as the Intersil 6100 family. By virtue of their CMOS technology they had low power requirements and were used in some embedded military systems, the PDP-8 combined low cost, simplicity, expandability, and careful engineering for value. The greatest historical significance was that the PDP-8s low cost and high volume made a computer available to new people for many new uses. Its continuing significance is as a example of value-engineered computer design. The low complexity brought other costs and it made programming cumbersome, as is seen in the examples in this article and from the discussion of pages and fields. Some ambitious programming projects failed to fit in memory or developed design defects that could not be solved, as design advances reduced the costs of logic and memory, the programmers time became relatively more important. Subsequent computer designs emphasized ease of programming, typically using a larger, eventually, most machine-language programming came to be generated by compilers and report generators. The PDP-8 used ideas from several 12-bit predecessors, most notably the LINC designed by W. A. Clark, the architecture has a simple programmed I/O bus, plus a DMA channel
11.
X86
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X86 is a family of backward-compatible instruction set architectures based on the Intel 8086 CPU and its Intel 8088 variant. The term x86 came into being because the names of several successors to Intels 8086 processor end in 86, many additions and extensions have been added to the x86 instruction set over the years, almost consistently with full backward compatibility. The architecture has been implemented in processors from Intel, Cyrix, AMD, VIA and many companies, there are also open implementations. In the 1980s and early 1990s, when the 8088 and 80286 were still in common use, today, however, x86 usually implies a binary compatibility also with the 32-bit instruction set of the 80386. An 8086 system, including such as 8087 and 8089. There were also terms iRMX, iSBC, and iSBX – all together under the heading Microsystem 80, however, this naming scheme was quite temporary, lasting for a few years during the early 1980s. Today, x86 is ubiquitous in both stationary and portable computers, and is also used in midrange computers, workstations, servers. A large amount of software, including operating systems such as DOS, Windows, Linux, BSD, Solaris and macOS, functions with x86-based hardware. There have been attempts, including by Intel itself, to end the market dominance of the inelegant x86 architecture designed directly from the first simple 8-bit microprocessors. Examples of this are the iAPX432, the Intel 960, Intel 860, however, the continuous refinement of x86 microarchitectures, circuitry and semiconductor manufacturing would make it hard to replace x86 in many segments. The table below lists processor models and model series implementing variations of the x86 instruction set, each line item is characterized by significantly improved or commercially successful processor microarchitecture designs. Such x86 implementations are seldom simple copies but often employ different internal microarchitectures as well as different solutions at the electronic, quite naturally, early compatible microprocessors were 16-bit, while 32-bit designs were developed much later. For the personal computer market, real quantities started to appear around 1990 with i386 and i486 compatible processors, other companies, which designed or manufactured x86 or x87 processors, include ITT Corporation, National Semiconductor, ULSI System Technology, and Weitek. Some early versions of these microprocessors had heat dissipation problems, AMD later managed to establish itself as a serious contender with the K6 set of processors, which gave way to the very successful Athlon and Opteron. There were also other contenders, such as Centaur Technology, Rise Technology, VIA Technologies energy efficient C3 and C7 processors, which were designed by the Centaur company, have been sold for many years. Centaurs newest design, the VIA Nano, is their first processor with superscalar and it was, perhaps interestingly, introduced at about the same time as Intels first in-order processor since the P5 Pentium, the Intel Atom. The instruction set architecture has twice been extended to a word size. In 1999-2003, AMD extended this 32-bit architecture to 64 bits and referred to it as x86-64 in early documents, Intel soon adopted AMDs architectural extensions under the name IA-32e, later using the name EM64T and finally using Intel 64
12.
Motorola 68000
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The Motorola 68000 is a 32-bit CISC microprocessor with a 16-bit external data bus, designed and marketed by Motorola Semiconductor Products Sector. After 38 years in production, the 68000 architecture is still in use, the 68000 grew out of the MACSS project, begun in 1976 to develop an entirely new architecture without backward compatibility. It would be a higher-power sibling complementing the existing 8-bit 6800 line rather than a compatible successor, in the end, the 68000 did retain a bus protocol compatibility mode for existing 6800 peripheral devices, and a version with an 8-bit data bus was produced. However, the designers focused on the future, or forward compatibility. For instance, the CPU registers are 32 bits wide, though few self-contained structures in the processor itself operate on 32 bits at a time. The MACSS team drew heavily on the influence of minicomputer processor design, such as the PDP-11 and VAX systems, in the mid 1970s, the 8-bit microprocessor manufacturers raced to introduce the 16-bit generation. National Semiconductor had been first with its IMP-16 and PACE processors in 1973–1975, Intel had worked on their advanced 16/32-bit Intel iAPX432 since 1975 and their Intel 8086 since 1976. Arriving late to the 16-bit arena afforded the new processor more transistors, 32-bit macroinstructions, the original MC68000 was fabricated using an HMOS process with a 3.5 µm feature size. Formally introduced in September 1979, Initial samples were released in February 1980, Initial speed grades were 4,6, and 8 MHz.10 MHz chips became available during 1981, and 12.5 MHz chips by June 1982. The 16.67 MHz 12F version of the MC68000, the fastest version of the original HMOS chip, was not produced until the late 1980s, tom Gunter, retired Corporate Vice President at Motorola, is known as the Father of the 68000. The 68000 was used in Microsoft Xenix systems as well as an early NetWare Unix-based Server, the 68000 was used in the first generation of desktop laser printers including the original Apple Inc. In 1982, the 68000 received an update to its ISA allowing it to virtual memory and to conform to the Popek. The updated chip was called the 68010, a further extended version which exposed 31 bits of the address bus was also produced, in small quantities, as the 68012. To support lower-cost systems and control applications with smaller sizes, Motorola introduced the 8-bit compatible MC68008. This was a 68000 with an 8-bit data bus and an address bus. After 1982, Motorola devoted more attention to the 68020 and 88000 projects, several other companies were second-source manufacturers of the HMOS68000. These included Hitachi, who shrank the size to 2.7 µm for their 12.5 MHz version, Mostek, Rockwell, Signetics, Thomson/SGS-Thomson. Toshiba was also a maker of the CMOS 68HC000
13.
CP/M
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Initially confined to single-tasking on 8-bit processors and no more than 64 kilobytes of memory, later versions of CP/M added multi-user variations and were migrated to 16-bit processors. The combination of CP/M and S-100 bus computers was loosely patterned on the MITS Altair and this computer platform was widely used in business through the late 1970s and into the mid-1980s. CP/M increased the size for both hardware and software by greatly reducing the amount of programming required to install an application on a new manufacturers computer. An important driver of innovation was the advent of low-cost microcomputers running CP/M, as independent programmers and hackers bought them. CP/M was displaced by MS-DOS soon after the 1981 introduction of the IBM PC, manufacturers of CP/M-compatible systems customized portions of the operating system for their own combination of installed memory, disk drives, and console devices. CP/M would also run on based on the Zilog Z80 processor since the Z80 was compatible with 8080 code. CP/M used the 7-bit ASCII set, the other 128 characters made possible by the 8-bit byte were not standardized. For example, one Kaypro used them for Greek characters, WordStar used the 8th bit as an end-of-word marker. The BIOS and BDOS were memory-resident, while the CCP was memory-resident unless overwritten by an application, a number of transient commands for standard utilities were also provided. The transient commands resided in files with the extension. COM on disk, the BIOS directly controlled hardware components other than the CPU and main memory. It contained functions such as input and output and the reading and writing of disk sectors. The BDOS implemented the CP/M file system and some input/output abstractions on top of the BIOS, the CCP took user commands and either executed them directly or loaded and started an executable file of the given name. Third-party applications for CP/M were also essentially transient commands, the BDOS, CCP and standard transient commands were the same in all installations of a particular revision of CP/M, but the BIOS portion was always adapted to the particular hardware. Adding memory to a computer, for example, meant that the CP/M system had to be reinstalled with an updated BIOS capable of addressing the additional memory, a utility was provided to patch the supplied BIOS, BDOS and CCP to allow them to be run from higher memory. Once installed, the system was stored in reserved areas at the beginning of any disk which would be used to boot the system. On start-up, the bootloader would load the system from the disk in drive A. By modern standards CP/M was primitive, owing to the constraints on program size. With version 1.0 there was no provision for detecting a changed disk, if a user changed disks without manually rereading the disk directory the system would write on the new disk using the old disks directory information, ruining the data stored on the disk
14.
MS-DOS
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MS-DOS is a discontinued operating system for x86-based personal computers mostly developed by Microsoft. MS-DOS resulted from a request in 1981 by IBM for a system to use in its IBM PC range of personal computers. Microsoft quickly bought the rights to 86-DOS from Seattle Computer Products, IBM licensed and released it in August 1981 as PC DOS1.0 for use in their PCs. During its life, several competing products were released for the x86 platform and it was also the underlying basic operating system on which early versions of Windows ran as a GUI. It is a operating system, and consumes negligible installation space. MS-DOS was a form of 86-DOS – owned by Seattle Computer Products. This first version was shipped in August 1980, Microsoft, which needed an operating system for the IBM Personal Computer hired Tim Paterson in May 1981 and bought 86-DOS1.10 for $75,000 in July of the same year. Microsoft kept the number, but renamed it MS-DOS. They also licensed MS-DOS1. 10/1.14 to IBM, within a year Microsoft licensed MS-DOS to over 70 other companies. It was designed to be an OS that could run on any 8086-family computer, thus, there were many different versions of MS-DOS for different hardware, and there is a major distinction between an IBM-compatible machine and an MS-DOS machine. This design would have worked well for compatibility, if application programs had only used MS-DOS services to perform device I/O, Microsoft omitted multi-user support from MS-DOS because Microsofts Unix-based operating system, Xenix, was fully multi-user. After the breakup of the Bell System, however, AT&T Computer Systems started selling UNIX System V, believing that it could not compete with AT&T in the Unix market, Microsoft abandoned Xenix, and in 1987 transferred ownership of Xenix to the Santa Cruz Operation. On 25 March 2014, Microsoft made the code to SCP MS-DOS1.25, as an April Fools joke in 2015, Microsoft Mobile launched a Windows Phone application called MS-DOS Mobile which was presented as a new mobile operating system and worked similar to MS-DOS. Version 3.1 – Support for Microsoft Networks Version 3.2 – First version to support 3.5 inch,720 kB floppy drives and diskettes. Version 3.21 Version 3.22 – Version 3.25 Version 3.3 – First version to support 3.5 inch,1.44 MB floppy drives and diskettes, Version 3. 3a Version 3.31 – supports FAT16B and larger drives. MS-DOS4.0 and MS-DOS4.1 – A separate branch of development with additional multitasking features and it is unrelated to any later versions, including versions 4.00 and 4.01 listed below MS-DOS4. x – includes a graphical/mouse interface. It had many bugs and compatibility issues. Version 4.00 – First version to support a hard disk partition that is greater than 32 MiB. Version 4.01 – Microsoft rewritten Version 4.00 released under MS-DOS label, First version to introduce volume serial number when formatting hard disks and floppy disks
15.
Unix
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Among these is Apples macOS, which is the Unix version with the largest installed base as of 2014. Many Unix-like operating systems have arisen over the years, of which Linux is the most popular, Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmer users. The system grew larger as the system started spreading in academic circles, as users added their own tools to the system. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration and these concepts are collectively known as the Unix philosophy. By the early 1980s users began seeing Unix as a universal operating system. Under Unix, the system consists of many utilities along with the master control program. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space, the microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a disk for storage and a data terminal for input and output. However, modern systems include networking and other new devices, as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, and semaphores. In microkernel implementations, functions such as network protocols could be moved out of the kernel, Multics introduced many innovations, but had many problems. Frustrated by the size and complexity of Multics but not by the aims and their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. The name Unics, a pun on Multics, was suggested for the project in 1970. Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, in 1972, Unix was rewritten in the C programming language. Bell Labs produced several versions of Unix that are referred to as Research Unix. In 1975, the first source license for UNIX was sold to faculty at the University of Illinois Department of Computer Science, UIUC graduate student Greg Chesson was instrumental in negotiating the terms of this license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to adoption of Unix by commercial startups, including Sequent, HP-UX, Solaris, AIX. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4, in the 1990s, Unix-like systems grew in popularity as Linux and BSD distributions were developed through collaboration by a worldwide network of programmers
16.
C (programming language)
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C was originally developed by Dennis Ritchie between 1969 and 1973 at Bell Labs, and used to re-implement the Unix operating system. C has been standardized by the American National Standards Institute since 1989, C is an imperative procedural language. Therefore, C was useful for applications that had formerly been coded in assembly language. Despite its low-level capabilities, the language was designed to encourage cross-platform programming, a standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with few changes to its source code. The language has become available on a wide range of platforms. In C, all code is contained within subroutines, which are called functions. Function parameters are passed by value. Pass-by-reference is simulated in C by explicitly passing pointer values, C program source text is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements. The C language also exhibits the characteristics, There is a small, fixed number of keywords, including a full set of flow of control primitives, for, if/else, while, switch. User-defined names are not distinguished from keywords by any kind of sigil, There are a large number of arithmetical and logical operators, such as +, +=, ++, &, ~, etc. More than one assignment may be performed in a single statement, function return values can be ignored when not needed. Typing is static, but weakly enforced, all data has a type, C has no define keyword, instead, a statement beginning with the name of a type is taken as a declaration. There is no function keyword, instead, a function is indicated by the parentheses of an argument list, user-defined and compound types are possible. Heterogeneous aggregate data types allow related data elements to be accessed and assigned as a unit, array indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects, they cannot be assigned or compared using single built-in operators, There is no array keyword, in use or definition, instead, square brackets indicate arrays syntactically, for example month. Enumerated types are possible with the enum keyword and they are not tagged, and are freely interconvertible with integers. Strings are not a data type, but are conventionally implemented as null-terminated arrays of characters. Low-level access to memory is possible by converting machine addresses to typed pointers
17.
VAX-11
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The VAX-11 was a family of minicomputers developed and manufactured by Digital Equipment Corporation using processors implementing the VAX instruction set architecture. The VAX-11/780 was the first VAX computer, the VAX-11/780, code-named Star, was introduced on 25 October 1977 at DECs Annual Meeting of Shareholders. It was the first computer to implement the VAX architecture, the VAX-11/780 central processing unit was built from transistor-transistor logic devices and had a 200 ns cycle time and a 2 kB cache. Memory and I/O were accessed via the Synchronous Backplane Interconnect, the VAX-11/780 supported 128 kB to 8 MB of memory through one or two memory controllers. Each memory controller supported 128 kB to 4 MB of memory, the memory was constructed from 4 or 16 kbit metal oxide semiconductor RAM chips mounted on memory array cards. Each memory controller controlled up to 16 array cards, the memory was protected by error correcting code. The VAX-11/780 used the Unibus and Massbus for I/O, Unibus was used for attaching peripherals and Massbus for disk and tape drives. Both buses were provided by adapters that interfaced the bus to the SBI, all systems came with one Unibus as standard, with up to four supported. Massbus was optional, with up to four supported, the VAX-11/780 also supported Computer Interconnect, a proprietary network to attach disk drives and potentially share them with other VAX computers. Later, this feature was used to connect VAX computers in a VMScluster, the VAX 11/782, code-named Atlas, was a dual-processor VAX-11/780 introduced in 1982. For multistream computation-intensive tasks the system delivered up to 1.8 times the performance of a VAX 11/780, the VAX-11/785, code-named superstar, was introduced in April 1984. It was essentially a faster VAX-11/780, with a CPU cycle time of 133 ns versus the 200 ns CPU cycle time of the VAX-11/780, the memory subsystem was also upgraded to support higher capacity memory boards. The VAX-11/787 was a variant of the VAX-11/785. The VAX-11/750, code-named Comet, was a compact, lower-performance TTL gate array–based implementation of the VAX architecture introduced in October 1980. The CPU had a 320 ns cycle time, introduced in April 1982, the VAX-11/730, code-named Nebula, was a still-more-compact, still-lower-performance bit slice implementation of the VAX architecture. Its CPU had a 270 ns cycle time, code-named LCN, it was a cost-reduced model of the VAX-11/730. Its CPU had a 270 ns cycle time, the Living Computer Museum of Seattle, Washington maintains a VAX-11/780-5 running OpenVMS6.2, which is available to interested parties via telnet. The Computer History Museum of Mountain View, California has three VAX-11/780 systems, one VAX-11/725, one VAX-11/730, and one VAX-11/750 within its permanent collection
18.
PDP-5
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Programmed Data Processor was a series of minicomputers made and marketed by the Digital Equipment Corporation from 1957 to 1990. So instead, Digital used their existing line of logic modules to build a Programmed Data Processor, the various PDP machines can generally be grouped into families based on word length. What is believed to be the first video game, Spacewar. was developed for this machine, along with the first known word processing program for a general-purpose computer, pDP-2 A number reserved for an unbuilt, undesigned 24-bit design. PDP-3 First DEC-designed 36-bit machine, though DEC did not offer it as a product, the only PDP-3 was built by the CIAs Scientific Engineering Institute in Waltham, MA to process radar cross section data for the Lockheed A-12 reconnaissance aircraft in 1960. Architecturally it was essentially a PDP-1 controlling a PDP-1 stretched to 36-bit word width, PDP-4 18-bit machine intended to be a slower, cheaper alternative to the PDP-1, it was not considered commercially successful. All later 18-bit PDP machines were based on a similar, but enlarged instruction set, more powerful, one customer of these early PDP machines was Atomic Energy of Canada. The installation at Chalk River, Ontario included an early PDP-4 with a display system, introduced the instruction set later expanded, in the PDP-8, to handle more bit rotations and to increase the maximum memory size from 4K words to 32K words. Very elegant architecture, introduced the set later used in the PDP-10. PDP-7 Replacement for the PDP-4, DECs first wire-wrapped machine, the first version of Unix, and the first version of B, a predecessor of C, were written for this machine at Bell Labs, as was the first version of MUMPS. PDP-8 12-bit machine with an instruction set, DECs first major commercial success. Many were purchased by schools, university departments, and research laboratories, later models were also used in the DECmate word processor and the VT-78 workstation. LINC-8 A hybrid of the LINC and PDP-8 computers, two instruction sets, PDP-9 Successor to the PDP-7, DECs first micro-programmed machine. It featured an increase of approximately twice that of the PDP-7. The PDP-9 was also one of the first small or medium scale computers to have a monitor system based on DIGITALs own small magnetic tape units. The PDP-9 established minicomputers as the edge of the computer industry. PDP-10 36-bit timesharing machine, and fairly successful over several different models, the instruction set was a slightly elaborated form of that of the PDP-6. PDP-11 The archetypal minicomputer, a 16-bit machine and another success for DEC. The LSI-11 was a four-chip PDP-11 used primarily for embedded systems, the 32-bit VAX series was descended from the PDP-11, and early VAX models had a PDP-11 compatibility mode
19.
LINC
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The LINC is a 12-bit, 2048-word computer. The LINC is considered the first minicomputer and a forerunner to the personal computer, originally named the Linc, suggesting the projects origins at MITs Lincoln Laboratory, it was renamed LINC after the project moved from the Lincoln Laboratory. The LINC was designed by Wesley A. Clark and Charles Molnar, the LINC and other MIT Group machines were designed at MIT and eventually built by Digital Equipment Corporation and Spear Inc. of Waltham, Massachusetts. The LINC sold for more than $40,000 at the time, a typical configuration included an enclosed 6X20 rack, four boxes holding tape drives, a small display, a control panel, and a keyboard. Although the LINCs instruction set was small, it was larger than the tiny PDP-8 instruction set, the LINC interfaced well with laboratory experiments. Analog inputs and outputs were part of the basic design and it was designed in 1962 by Charles Molnar and Wesley Clark at Lincoln Laboratory, Massachusetts, for NIH researchers. The LINCs design was literally in the domain, perhaps making it unique in the history of computers. The number of LINCs and who built them is a subject of debate in the 12-bit-word community. One account states that a dozen LINC computers were assembled by their eventual biologist users in a 1963 summer workshop at MIT, Digital Equipment Corporation and Spear Inc. of Waltham, MA. manufactured them commercially. DECs pioneer C. Gordon Bell states that the LINC project began in 1961, with first delivery in March 1962, a total of 50 were built, most at Lincoln Labs, housing the desktop instruments in four wooden racks. The first LINC included two oscilloscope displays, twenty-one were sold by DEC at $43,600, delivered in the Production Model design. The standard program development software was designed by Mary Allen Wilkes, the LINC control panel was used for single-stepping through programs and for program debugging. Execution could be stopped when the program counter matched a set of switches, another function allowed execution to be stopped when a particular address was accessed. The single-step and the functions could be automatically repeated. The repetition rate could be varied over four orders of magnitude by means of an analog knob, running a program at one step per second and gradually accelerating it to full speed provided an extremely dramatic way to experience and appreciate the speed of the computer. A noteworthy feature of the LINC was the LINCtape and it was a fundamental part of the machine design, not an optional peripheral, and the machines OS relied on it. The LINCtape can be compared to a linear diskette with a slow seek time, the magnetic tape drives on large machines of the day stored large quantities of data, took minutes to spool from end to end, but could not reliably update blocks of data in place. The tape was formatted in fixed-sized blocks, and was used to hold a directory, a single hardware instruction could seek and then read or write multiple tape blocks all in one operation
20.
PDP-4
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Programmed Data Processor was a series of minicomputers made and marketed by the Digital Equipment Corporation from 1957 to 1990. So instead, Digital used their existing line of logic modules to build a Programmed Data Processor, the various PDP machines can generally be grouped into families based on word length. What is believed to be the first video game, Spacewar. was developed for this machine, along with the first known word processing program for a general-purpose computer, pDP-2 A number reserved for an unbuilt, undesigned 24-bit design. PDP-3 First DEC-designed 36-bit machine, though DEC did not offer it as a product, the only PDP-3 was built by the CIAs Scientific Engineering Institute in Waltham, MA to process radar cross section data for the Lockheed A-12 reconnaissance aircraft in 1960. Architecturally it was essentially a PDP-1 controlling a PDP-1 stretched to 36-bit word width, PDP-4 18-bit machine intended to be a slower, cheaper alternative to the PDP-1, it was not considered commercially successful. All later 18-bit PDP machines were based on a similar, but enlarged instruction set, more powerful, one customer of these early PDP machines was Atomic Energy of Canada. The installation at Chalk River, Ontario included an early PDP-4 with a display system, introduced the instruction set later expanded, in the PDP-8, to handle more bit rotations and to increase the maximum memory size from 4K words to 32K words. Very elegant architecture, introduced the set later used in the PDP-10. PDP-7 Replacement for the PDP-4, DECs first wire-wrapped machine, the first version of Unix, and the first version of B, a predecessor of C, were written for this machine at Bell Labs, as was the first version of MUMPS. PDP-8 12-bit machine with an instruction set, DECs first major commercial success. Many were purchased by schools, university departments, and research laboratories, later models were also used in the DECmate word processor and the VT-78 workstation. LINC-8 A hybrid of the LINC and PDP-8 computers, two instruction sets, PDP-9 Successor to the PDP-7, DECs first micro-programmed machine. It featured an increase of approximately twice that of the PDP-7. The PDP-9 was also one of the first small or medium scale computers to have a monitor system based on DIGITALs own small magnetic tape units. The PDP-9 established minicomputers as the edge of the computer industry. PDP-10 36-bit timesharing machine, and fairly successful over several different models, the instruction set was a slightly elaborated form of that of the PDP-6. PDP-11 The archetypal minicomputer, a 16-bit machine and another success for DEC. The LSI-11 was a four-chip PDP-11 used primarily for embedded systems, the 32-bit VAX series was descended from the PDP-11, and early VAX models had a PDP-11 compatibility mode
21.
ASCII
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ASCII, abbreviated from American Standard Code for Information Interchange, is a character encoding standard. ASCII codes represent text in computers, telecommunications equipment, and other devices, most modern character-encoding schemes are based on ASCII, although they support many additional characters. ASCII was developed from telegraph code and its first commercial use was as a seven-bit teleprinter code promoted by Bell data services. Work on the ASCII standard began on October 6,1960, the first edition of the standard was published in 1963, underwent a major revision during 1967, and experienced its most recent update during 1986. Compared to earlier telegraph codes, the proposed Bell code and ASCII were both ordered for more convenient sorting of lists, and added features for other than teleprinters. Originally based on the English alphabet, ASCII encodes 128 specified characters into seven-bit integers as shown by the ASCII chart above. The characters encoded are numbers 0 to 9, lowercase letters a to z, uppercase letters A to Z, basic punctuation symbols, control codes that originated with Teletype machines, for example, lowercase j would become binary 1101010 and decimal 106. ASCII includes definitions for 128 characters,33 are non-printing control characters that affect how text and space are processed and 95 printable characters, of these, the IANA encourages use of the name US-ASCII for Internet uses of ASCII. The ASA became the United States of America Standards Institute and ultimately the American National Standards Institute, there was some debate at the time whether there should be more control characters rather than the lowercase alphabet. The X3.2.4 task group voted its approval for the change to ASCII at its May 1963 meeting, the X3 committee made other changes, including other new characters, renaming some control characters and moving or removing others. ASCII was subsequently updated as USAS X3. 4-1967, then USAS X3. 4-1968, ANSI X3. 4-1977 and they proposed a 9-track standard for magnetic tape, and attempted to deal with some punched card formats. The X3.2 subcommittee designed ASCII based on the earlier teleprinter encoding systems, like other character encodings, ASCII specifies a correspondence between digital bit patterns and character symbols. This allows digital devices to communicate each other and to process, store. Before ASCII was developed, the encodings in use included 26 alphabetic characters,10 numerical digits, ITA2 were in turn based on the 5-bit telegraph code Émile Baudot invented in 1870 and patented in 1874. The committee debated the possibility of a function, which would allow more than 64 codes to be represented by a six-bit code. In a shifted code, some character codes determine choices between options for the character codes. It allows compact encoding, but is reliable for data transmission. The standards committee decided against shifting, and so ASCII required at least a seven-bit code, the committee considered an eight-bit code, since eight bits would allow two four-bit patterns to efficiently encode two digits with binary-coded decimal
22.
Data General
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Data General was one of the first minicomputer firms from the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation and their first product, the Data General Nova, was a 16-bit minicomputer. The Nova was followed by the Supernova and Eclipse product lines, the company employed an original equipment manufacturer sales strategy to sell to third parties who incorporated Data General computers into the OEMs specific product lines. The company did continue into the 1990s, however, and was acquired by EMC Corporation in 2002. Data General was founded by engineers from Digital Equipment Corporation who were frustrated with DECs management. The chief founders were Edson de Castro, Henry Burkhardt III, and Richard Sogge of Digital Equipment, the company was founded in Hudson, Massachusetts in 1968. Edson de Castro was the engineer in charge of the PDP-8. It was designed specifically to be used in laboratory equipment settings, as the technology improved, many PDP-8s still operated decades later. De Castro, convinced he could do one better, began work on his new 16-bit design, the result was released in 1969 as the Nova. Designed to be rack-mounted similarly to the later PDP-8 machines, it was smaller in height, with the initial success of the Nova, Data General went public in the fall of 1969. The Nova, like the PDP-8, used a simple accumulator-based architecture, the original Nova was soon followed by the faster SuperNova, then later by several minor versions based on the SuperNova core. The last major version, the Nova 4, was released in 1978, during this period the Nova generated 20% annual growth rates for the company, becoming a star in the business community and generating US$100 million in sales in 1975. In 1977, DG launched a 16-bit microcomputer called the microNOVA to poor commercial success, the Nova series plays a very important role as instruction-set inspiration to Charles P. Thacker and others at Xerox PARC during their construction of the Xerox Alto. In 1974, the Nova was supplanted by their upscale 16-bit machine, based on many of the same concepts as the Nova, it included support for virtual memory and multitasking more suitable to the small office environment. For this reason, the Eclipse was packaged differently, in a case resembling a small refrigerator. Production problems with the Eclipse led to a rash of lawsuits in the late 1970s, newer versions of the machine were pre-ordered by many of DGs customers, which were never delivered. Many customers sued Data General after more than a year of waiting, charging the company with breach of contract, while others simply canceled their orders and went elsewhere. Strong demand continued for the Nova series, resulting in the Nova 4, in 1976, Digital announced the VAX series, their first 32-bit minicomputer line, described as super-minis
23.
Data General Nova
–
The Data General Nova was a popular 16-bit minicomputer released by the American company Data General in 1968. The Nova was packaged into a rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world and it was succeeded by the Data General Eclipse, which was similar in most ways but added virtual memory support and other features required by modern operating systems. Edson de Castro was the Product Manager at Digital Equipment Corporation of their pioneering PDP-8, the fourth founder, Herbert Richman, had been a salesman for Fairchild Semiconductor and knew the others through his contacts with Digital Equipment. This greatly reduced costs over the traditional wire-wrapping technique, the larger-board construction also made the Nova more reliable, which made it especially attractive for industrial or lab settings. Fairchild Semiconductor provided the new medium-scale integration chips used throughout the system, the Nova was one of the first 16-bit minicomputers and was a leader in moving to word lengths that were multiples of the 8-bit byte in that market. DG released the Nova in 1969 at a price of US$3,995. The basic model was not very useful out of the box, starting in 1969, Data General shipped a total of 50,000 Novas at $8000 each. The Nova’s biggest competition was from the new DEC PDP-11 computer series, the Nova became popular in scientific and laboratory uses. The Nova 1200 executed core memory access instructions in 2.55 microseconds, use of read only memory saved 0.4 μs. Accumulator instructions took 1.55 μs, MUL2.55 μs, DIV3.75 μs, ISZ3. 15-4.5 μs. On the later Eclipse MV/6000, LDA and STA took 0.44 μs, ADD, etc. took 0.33 μs, MUL2.2 μs, DIV3.19 μs, ISZ1.32 μs, FAD5.17 μs, FMMD11.66 μs. Bob Supnik’s SimH project – Includes a basic Nova emulator in a user-modifiable package The portable C compiler includes a NOVA target, a portable PDP-8 and DG Nova cross-assembler Carl Friend’s Minicomputer Museum – Describes the Nova instruction set in detail
24.
Integrated circuit
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An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material, normally silicon. The ICs mass production capability, reliability and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of using discrete transistors. ICs are now used in all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other home appliances are now inextricable parts of the structure of modern societies, made possible by the small size. These advances, roughly following Moores law, allow a computer chip of 2016 to have millions of times the capacity, ICs have two main advantages over discrete circuits, cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography rather than being constructed one transistor at a time, furthermore, packaged ICs use much less material than discrete circuits. Performance is high because the ICs components switch quickly and consume little power because of their small size, the main disadvantage of ICs is the high cost to design them and fabricate the required photomasks. This high initial cost means ICs are only practical when high production volumes are anticipated, Circuits meeting this definition can be constructed using many different technologies, including thin-film transistor, thick film technology, or hybrid integrated circuit. However, in general usage integrated circuit has come to refer to the single-piece circuit construction originally known as a integrated circuit. Jacobi disclosed small and cheap hearing aids as typical industrial applications of his patent, an immediate commercial use of his patent has not been reported. The idea of the circuit was conceived by Geoffrey Dummer. Dummer presented the idea to the public at the Symposium on Progress in Quality Electronic Components in Washington and he gave many symposia publicly to propagate his ideas, and unsuccessfully attempted to build such a circuit in 1956. A precursor idea to the IC was to create small ceramic squares, Components could then be integrated and wired into a bidimensional or tridimensional compact grid. This idea, which seemed very promising in 1957, was proposed to the US Army by Jack Kilby, however, as the project was gaining momentum, Kilby came up with a new, revolutionary design, the IC. In his patent application of 6 February 1959, Kilby described his new device as a body of semiconductor material … wherein all the components of the circuit are completely integrated. The first customer for the new invention was the US Air Force, Kilby won the 2000 Nobel Prize in Physics for his part in the invention of the integrated circuit. His work was named an IEEE Milestone in 2009, half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilbys had not. Noyces design was made of silicon, whereas Kilbys chip was made of germanium, Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation, a key concept behind the IC
25.
DEC J-11
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The J-11 is a microprocessor chip set that implements the PDP-11 instruction set architecture jointly developed by Digital Equipment Corporation and Harris Semiconductor. It was a chip set designed to integrate the performance. It was used in the PDP-11/73, PDP-11/83 and Professional 380 and it consisted of a data path chip and a control chip in ceramic leadless packages mounted on a single ceramic hybrid DIP package. The control chip incorporated a sequencer and a microcode ROM. An optional separate floating-point acclerator chip could be used, and was packaged in a standard DIP, the data path chip and control chip were fabricated by Harris in a CMOS process while the FPA was fabricated by Digital in their ZMOS NMOS process. A clone of the J-11 was manufactured in the Soviet Union under the designation KN1831VM1
26.
Bus (computing)
–
In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related components and software, including communication protocols. Modern computer buses can use both parallel and bit serial connections, and can be wired in either a multidrop or daisy chain topology, or connected by switched hubs, as in the case of USB. An early computer might contain a hand-wired CPU of vacuum tubes, a drum for main memory. In both examples, computer buses of one form or another move data between all of these devices, in most traditional computer architectures, the CPU and main memory tend to be tightly coupled. In most cases, the CPU and memory share signalling characteristics, the bus connecting the CPU and memory is one of the defining characteristics of the system, and often referred to simply as the system bus. It is possible to allow peripherals to communicate with memory in the same fashion and this is commonly accomplished through some sort of standardized electrical connector, several of these forming the expansion bus or local bus. However, as the differences between the CPU and peripherals varies widely, some solution is generally needed to ensure that peripherals do not slow overall system performance. Many CPUs feature a set of pins similar to those for communicating with memory. Others use smart controllers to place the data directly in memory, most modern systems combine both solutions, where appropriate. As the number of potential peripherals grew, using a card for every peripheral became increasingly untenable. This has led to the introduction of bus systems designed specifically to support multiple peripherals, common examples are the SATA ports in modern computers, which allow a number of hard drives to be connected without the need for a card. However, these systems are generally too expensive to implement in low-end devices. This has led to the development of a number of low-performance bus systems for these solutions. All such examples may be referred to as peripheral buses, although this terminology is not universal, in modern systems the performance difference between the CPU and main memory has grown so great that increasing amounts of high-speed memory is built directly into the CPU, known as a cache. These system buses are used to communicate with most other peripherals, through adaptors. Such systems are more similar to multicomputers, communicating over a bus rather than a network. In these cases, expansion buses are entirely separate and no longer share any architecture with their host CPU, what would have formerly been a system bus is now often known as a front-side bus
27.
System bus
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The technique was developed to reduce costs and improve modularity, and although popular in the 1970s and 1980s, more modern computers use a variety of separate buses adapted to more specific needs. Many early electronic computers were based on the First Draft of a Report on the EDVAC report published in 1945, the Report presented a general organization and theoretical model of the computer, however, not the implementation of that model. Soon designs integrated the control unit and ALU into what became known as the processing unit. Computers in the 1950s and 1960s were generally constructed in an ad-hoc fashion, for example, the CPU, memory, and input/output units were each one or more cabinets connected by cables. Engineers used the techniques of standardized bundles of wires and extended the concept as backplanes were used to hold printed circuit boards in these early machines. The name bus was used for bus bars that carried electrical power to the various parts of electric machines. The advent of integrated circuits vastly reduced the size of each computer unit, Standard modules could be interconnected in more uniform ways and were easier to develop and maintain. To provide even more modularity with reduced cost, memory and I/O buses were combined into a single unified system bus. Modularity and cost became important as computers became small enough to fit in a single cabinet, digital Equipment Corporation further reduced cost for mass-produced minicomputers, and memory-mapped I/O into the memory bus, so that the devices appeared to be memory locations. This was implemented in the Unibus of the PDP-11 around 1969, even computers such as the PDP-8 without memory-mapped I/O were soon implemented with a system bus, which allowed modules to be plugged into any slot. Some authors called this a new streamlined model of computer architecture, many early microcomputers were built with a single system bus, starting with the S-100 bus in the Altair 8800 computer system in about 1975. The IBM PC used the Industry Standard Architecture bus as its bus in 1981. The passive backplanes of early models were replaced with the standard of putting the CPU and RAM on a motherboard, the Multibus became a standard of the Institute of Electrical and Electronics Engineers as IEEE standard 796 in 1983. Sun Microsystems developed the SBus in 1989 to support smaller expansion cards, the easiest way to implement symmetric multiprocessing was to plug in more than one CPU into the shared system bus, which was used through the 1980s. However, the bus quickly became the bottleneck and more sophisticated connection techniques were explored. This was introduced in the Pentium Pro and Pentium II products in the mid to late 1990s, the primary bus for communicating data between the CPU and main memory and input and output devices is called the front-side bus, and the back-side bus accesses the level 2 cache. The systems bus can even be internal to an integrated circuit. Examples include AMBA, CoreConnect, and Wishbone
28.
Alcatel-Lucent
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Alcatel-Lucent S. A. was a French global telecommunications equipment company, headquartered in Boulogne-Billancourt, France. As of January 2016, the company is part of Nokia, the company focused on fixed, mobile and converged networking hardware, IP technologies, software and services, with operations in more than 130 countries. Alcatel-Lucents chief executive officer was Michel Combes and the chairman of the board was Philippe Camus. Camus joined the company in the quarter of 2008, alongside Ben Verwaayen as CEO, after Alcatel-Lucents first CEO Patricia Russo. For 2010, the company had revenues of €16 billion and a net loss of €334 million. For 2011, revenues were €15 billion, net loss of €1.1 billion, for 2012, revenues were €14.4 billion and net loss of €1.4 billion. On October 1,2014, it announced that it had closed the sale of its subsidiary Alcatel-Lucent Enterprise to China Huaxin Post & Telecommunication Economy Development Center, Alcatel-Lucent was formed when Alcatel merged with Lucent Technologies on December 1,2006. However, the predecessors of the company have been a part of industry since the late 19th century. The company has roots in two early telecommunications companies, La Compagnie Générale dElectricité and the Western Electric Manufacturing Company, Western Electric began in 1869 when Elisha Gray and Enos N. Barton started a manufacturing firm based in Cleveland, Ohio. By 1880, the company had relocated to Chicago, Illinois, CGE would become a leader in digital communications and would also be known for producing the TGV high-speed trains in France. Bell Telephone Laboratories was created in 1925 from the consolidation of the R&D organizations of Western Electric, Bell Labs researchers have won 7 Nobel Prizes. Also in 1925, Western Electric sold its International Western Electric Company subsidiary to ITT Corporation, CGE purchased the telecommunications part of ITT in the mid-1980s. AT&T re-entered the European telecommunications market in 1984 following the Bell System divestiture, Philips promoted the venture in part because its PRX public switching technology was ageing and it sought a partner to help fund the development costs of digital switching. In 1987, AT&T increased its holding to 60% and in 1990 it purchased the remainder of the Philips holding, in 1998, Alcatel Alsthom shifted its focus to the telecommunications industry, spinning off its Alsthom activities and changing the companys name to Alcatel. AT&T spun off Lucent Technologies in April 1996 with a public offering. In April 2004, TCL Corporation and Alcatel announced the creation of a mobile phone manufacturing joint venture, facing intense competition in the telecommunications industry, Alcatel and Lucent Technologies merged on November 30,2006. On April 5,2006, Alcatel announced that it would swap its shares of Alcatel Alenia Space and Telespazio for €673 million and a 12. 1% stake in Thales and this increased Alcatels stake in Thales to 20. 8%
29.
International Bell Telephone Company
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IBTC rapidly evolved into an important European telephone service provider and manufacturer, with major operations in several countries. AT&T, its U. S. parent, later sold its entire European division and IBTCs subsidiaries to the International Telephone & Telegraph Company of Cuba in 1925, ending a 46-year presence on the Continent. During his tour of the continent the Belgian government offered him the greatest financial incentives to establish his European subsidiarys headquarters in their country, BTMC was created as a joint venture by the International Bell Telephone Company of New York and the Western Electric Company of Chicago. BTMC came under majority ownership by the telephone manufacturer Western Electric, Western Electric was itself later majority owned by the American Bell Telephone Company, returning control of BTMC back to the Bell organization. BTMC was owned 45% by American Bell Telephone, and 55% by Bells major U. S. supplier, Western Electric, a U. S. company formed during the era of the telegraph, became American Bells sole telephone supplier the same year. Barton had earlier sent him to Australia and New Zealand to help with operations there, Welles would lead the overseas BTMC company for the next 30 years assisted by Louis De Groof, a Belgian authorised agent. IBTC started up subsidiary manufacturing plants in cities throughout all of Europe. In the year after its founding BTMC employed 35 people, and its workshops were accommodated within a plant at No.4 Boudewijnstraat. The Antwerp facility was responsible for introducing the telephone to much of Europe, with its first manual. In 1884 the very first European intercity line was created between Antwerp and Brussels, and in 1887 the first international line in Europe was opened between Brussels and Paris, francis Welles retired from BTMC in 1913 and returned to the United States shortly before the First World War. Welles and was succeeded by Alexis Mois, the Great War inflicted severe damage to BTMCs operations and production facilities, much of which was destroyed or seized by the invading German army. The companys U. S. managers immediately departed for the United Kingdom or returned home, while many plant employees had been seconded to the Belgian army, or moved to other unoccupied countries. In its early existence the Bell Telephone Manufacturing Company of Belgium took on the role of a child of two often squabbling parents, Western Electric and the American Bell Telephone Company. However even through a succession of owners the BTMC has retained its original name, the first telephone exchanges in Belgium were opened in 1878. A company was formed in Brussels in 1879, and others followed, competition was recognised as unsatisfactory, and the various companies were encouraged to amalgamate. The Compagnie Belge du Téléphone Bell was formed in 1882, as the Belgian subsidiary of the International Bell Telephone Company of New York. By the end of 1886, the Belgian division had a total 6,900 kilometers of lines, and 3,532 subscribers in seven cities, including Brussels, Antwerp, Charleroi, Ghent, Verviers. The first exchange in Switzerland was opened in Zurich, operated under a license granted by the IBTC to a group of men on July 24,1880
30.
X.25
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X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, X.25 is a family of protocols that was popular during the 1980s with telecommunications companies and in financial transaction systems such as automated teller machines. X.25 was originally defined by the International Telegraph and Telephone Consultative Committee in a series of drafts and finalized in a publication known as The Orange Book in 1976. While X.25 has, to an extent, been replaced by less complex protocols, especially the Internet protocol. X.25 is one of the oldest packet-switched services available and it was developed before the OSI Reference Model. The protocol suite is designed as three conceptual layers, which correspond closely to the three layers of the seven-layer OSI model. It also supports functionality not found in the OSI network layer, X.25 was developed in the ITU-T Study Group VII based upon a number of emerging data network projects. Various updates and additions were worked into the standard, eventually recorded in the ITU series of books describing the telecommunication systems. These books were published every year with different-colored covers. The X.25 specification is only part of the set of X-Series specifications on public data networks. The public data network was the name given to the international collection of X.25 providers. Their combined network had large global coverage during the 1980s and into the 1990s, publicly accessible X.25 networks were set up in most countries during the 1970s and 1980s, to lower the cost of accessing various online services. Beginning in the early 1990s, in North America, use of X.25 networks started to be replaced by Frame Relay, most systems that required X.25 now use TCP/IP, however it is possible to transport X.25 over TCP/IP when necessary. X.25 networks are still in use throughout the world, a variant called AX.25 is also used widely by amateur packet radio. Racal Paknet, now known as Widanet, is still in operation in many regions of the world, running on an X.25 protocol base. Additionally X.25 is still under heavy use in the business even though a transition to modern protocols like X.400 is without option as X.25 hardware becomes increasingly rare. As recently as March 2006, the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with Air Route Traffic Control Centers, france was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as Minitel it was based on Videotex, itself running on X.25, as planned, service was terminated 30 June 2012
31.
Central processing unit
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The computer industry has used the term central processing unit at least since the early 1960s. The form, design and implementation of CPUs have changed over the course of their history, most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit chip. An IC that contains a CPU may also contain memory, peripheral interfaces, some computers employ a multi-core processor, which is a single chip containing two or more CPUs called cores, in that context, one can speak of such single chips as sockets. Array processors or vector processors have multiple processors that operate in parallel, there also exists the concept of virtual CPUs which are an abstraction of dynamical aggregated computational resources. Early computers such as the ENIAC had to be rewired to perform different tasks. Since the term CPU is generally defined as a device for software execution, the idea of a stored-program computer was already present in the design of J. Presper Eckert and John William Mauchlys ENIAC, but was initially omitted so that it could be finished sooner. On June 30,1945, before ENIAC was made, mathematician John von Neumann distributed the paper entitled First Draft of a Report on the EDVAC and it was the outline of a stored-program computer that would eventually be completed in August 1949. EDVAC was designed to perform a number of instructions of various types. Significantly, the programs written for EDVAC were to be stored in high-speed computer memory rather than specified by the wiring of the computer. This overcame a severe limitation of ENIAC, which was the considerable time, with von Neumanns design, the program that EDVAC ran could be changed simply by changing the contents of the memory. Early CPUs were custom designs used as part of a larger, however, this method of designing custom CPUs for a particular application has largely given way to the development of multi-purpose processors produced in large quantities. This standardization began in the era of discrete transistor mainframes and minicomputers and has accelerated with the popularization of the integrated circuit. The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers, both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in electronic devices ranging from automobiles to cellphones, the so-called Harvard architecture of the Harvard Mark I, which was completed before EDVAC, also utilized a stored-program design using punched paper tape rather than electronic memory. Relays and vacuum tubes were used as switching elements, a useful computer requires thousands or tens of thousands of switching devices. The overall speed of a system is dependent on the speed of the switches, tube computers like EDVAC tended to average eight hours between failures, whereas relay computers like the Harvard Mark I failed very rarely. In the end, tube-based CPUs became dominant because the significant speed advantages afforded generally outweighed the reliability problems, most of these early synchronous CPUs ran at low clock rates compared to modern microelectronic designs. Clock signal frequencies ranging from 100 kHz to 4 MHz were very common at this time, the design complexity of CPUs increased as various technologies facilitated building smaller and more reliable electronic devices
32.
Interrupt
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In system programming, an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. An interrupt alerts the processor to a high-priority condition requiring the interruption of the current code the processor is executing, the processor responds by suspending its current activities, saving its state, and executing a function called an interrupt handler to deal with the event. This interruption is temporary, and, after the interrupt handler finishes, there are two types of interrupts, hardware interrupts and software interrupts. Hardware interrupts are used by devices to communicate that they require attention from the operating system, for example, pressing a key on the keyboard or moving the mouse triggers hardware interrupts that cause the processor to read the keystroke or mouse position. Unlike the software type, hardware interrupts are asynchronous and can occur in the middle of instruction execution, the act of initiating a hardware interrupt is referred to as an interrupt request. A software interrupt is caused either by a condition in the processor itself. The former is called a trap or exception and is used for errors or events occurring during program execution that are exceptional enough that they cannot be handled within the program itself. For example, an exception will be thrown if the processors arithmetic logic unit is commanded to divide a number by zero as this instruction is in error. The operating system will catch this exception, and can choose to abort the instruction, each interrupt has its own interrupt handler. The number of interrupts is limited by the number of interrupt request lines to the processor. Interrupts are a commonly used technique for computer multitasking, especially in real-time computing, such a system is said to be interrupt-driven. Hardware interrupts were introduced as an optimization, eliminating unproductive waiting time in polling loops and they may be implemented in hardware as a distinct system with control lines, or they may be integrated into the memory subsystem. If implemented as part of the controller, interrupts are mapped into the systems memory address space. Interrupts can be categorized into different types, Maskable interrupt. Non-maskable interrupt, an interrupt that lacks an associated bit-mask. NMIs are used for the highest priority tasks such as timers, inter-processor interrupt, a special case of interrupt that is generated by one processor to interrupt another processor in a multiprocessor system. Software interrupt, an interrupt generated within a processor by executing an instruction, software interrupts are often used to implement system calls because they result in a subroutine call with a CPU ring level change. Spurious interrupt, an interrupt that is unwanted
33.
Wire wrap
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Wire wrap is a method to construct electronic circuit boards. Wires can be wrapped by hand or by machine, and can be hand-modified afterwards and it was popular for large-scale manufacturing in the 60s and early 70s, and continues to be used for short runs and prototypes. The method eliminates the design and fabrication of a circuit board. Wire wrapping is unusual among other prototyping technologies since it allows for complex assemblies to be produced by automated equipment, the connections themselves are firmer and have lower electrical resistance due to cold welding of the wire to the terminal post at the corners. Wire wrap was used for assembly of high frequency prototypes and small runs, including gigahertz microwave circuits. It is unique among automated prototyping techniques in that wire lengths can be exactly controlled, Wire wrap construction became popular around 1960 in circuit board manufacturing, and use has now sharply declined. Surface-mount technology has made the technique much less useful than in previous decades, solder-less breadboards and the decreasing cost of professionally made PCBs have nearly eliminated this technology. A correctly made wire-wrap connection for 30 or 28 AWG wire is seven turns of wire with half to one. The square hard-gold-plated post thus forms 28 redundant contacts, the silver-plated wire coating cold-welds to the gold. If corrosion occurs, it occurs on the outside of the wire, a correctly designed wire-wrap tool applies up to twenty tons of force per square inch on each joint. The electronic parts sometimes plug into sockets, the sockets are attached with cyanoacrylate to thin plates of glass-fiber-reinforced epoxy. The usual posts are 0.025 in square,1 in high, premium posts are hard-drawn beryllium copper alloy plated with a 0.000025 in of gold to prevent corrosion. Less-expensive posts are bronze with tin plating,30 gauge silver-plated soft copper wire is insulated with a fluorocarbon that does not emit dangerous gases when heated. The most common insulation is Kynar, the 30 AWG Kynar wire is cut into standard lengths, then one inch of insulation is removed on each end. A wire wrap tool has two holes, the wire and 1⁄4 in of insulated wire are placed in a hole near the edge of the tool. The hole in the center of the tool is placed over the post, the result is that 1.5 to 2 turns of insulated wire are wrapped around the post, and above that,7 to 9 turns of bare wire are wrapped around the post. The post has room for three such connections, although only one or two are needed. This permits manual wire-wrapping to be used for repairs, the turn and a half of insulated wire helps prevent wire fatigue where it meets the post
34.
Backplane
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A backplane is a group of electrical connectors in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a computer system. Backplanes commonly use a circuit board, but wire-wrapped backplanes have also been used in minicomputers. Early microcomputer systems like the Altair 8800 used a backplane for the processor, a backplane is generally differentiated from a motherboard by the lack of on-board processing and storage elements. A backplane uses plug-in cards for storage and processing, backplanes are normally used in preference to cables because of their greater reliability. In a cabled system, the cables need to be flexed every time that a card is added or removed from the system, a backplane does not suffer from this problem, so its service life is limited only by the longevity of its connectors. For example, the DIN41612 connectors used in the VMEbus system can withstand 50 to 500 insertions and removals, to transmit information, Serial Back-Plane technology uses a low voltage differential signaling transmission method for sending information. These cable sets have a board located in the computer, an expansion board in the remote backplane. Backplanes have grown in complexity from the simple Industry Standard Architecture or S-100 style where all the connectors were connected to a common bus, due to limitations inherent in the Peripheral Component Interconnect specification for driving slots, backplanes are now offered as passive and active. True passive backplanes offer no active bus driving circuitry, any desired arbitration logic is placed on the daughter cards. Active backplanes include chips which buffer the various signals to the slots, the distinction between the two isnt always clear, but may become an important issue if a whole system is expected to not have a single point of failure. A passive backplane, even if it is single, is not usually considered a SPOF, active backplanes are more complicated and thus have a non-zero risk of malfunction. While there are a few motherboards that offer more than 8 slots, in addition, as technology progresses, the availability and number of a particular slot type may be limited in terms of what is currently offered by motherboard manufacturers. However, backplane architecture is somewhat unrelated to the SBC technology plugged into it, there are some limitations to what can be constructed, in that the SBC chip set and processor have to provide the capability of supporting the slot types. In addition, virtually an unlimited number of slots can be provided with 20, including the SBC slot, as a practical though not an absolute limit. Thus, a PICMG backplane can provide any number and any mix of ISA, PCI, PCI-X, for example, an SBC with the latest i7 processor could interface with a backplane providing up to 19 ISA slots to drive legacy I/O cards. Some backplanes are constructed with slots for connecting to devices on both sides, and are referred to as midplanes and this ability to plug cards into either side of a midplane is often useful in larger systems made up primarily of modules attached to the midplane. Midplanes are often used in computers, mostly in blade servers, where server blades reside on one side, orthogonal midplanes connect vertical cards on one side to horizontal boards on the other side
35.
Printed circuit board
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Components are generally soldered on the PCB. Advanced PCBs may contain components embedded in the substrate, PCBs can be single sided, double sided or multi-layer. Conductors on different layers are connected with vias, multi-layer PCBs allow for much higher component density. FR-4 glass epoxy is the primary insulating substrate, a basic building block of the PCB is an FR-4 panel with a thin layer of copper foil laminated to one or both sides. In multi-layer boards multiple layers of material are laminated together, printed circuit boards are used in all but the simplest electronic products. Alternatives to PCBs include wire wrap and point-to-point construction, PCBs require the additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Manufacturing circuits with PCBs is cheaper and faster than other wiring methods as components are mounted and wired with one single part. A minimal PCB with a component used for easier prototyping is called a breakout board. When the board has no embedded components it is correctly called a printed wiring board or etched wiring board. However, the printed wiring board has fallen into disuse. A PCB populated with electronic components is called a printed circuit assembly, the IPC preferred term for assembled boards is circuit card assembly, and for assembled backplanes it is backplane assemblies. The term PCB is used both for bare and assembled boards. The world market for bare PCBs exceeded $60.2 billion in 2014, initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the diagram the component pin pads were laid out on the mylar. Rub-on dry transfers of common component footprints increased efficiency, traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout, to fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards. Modern PCBs are designed with dedicated software, generally in the following steps. Card dimensions and template are decided based on required circuitry and case of the PCB, the positions of the components and heat sinks are determined
36.
Western Digital
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Western Digital Corporation is an American computer data storage company and one of the largest computer hard disk drive manufacturers in the world, along with Seagate Technology. Western Digital Corporation has a history in the electronics industry as an integrated circuit maker. Western Digital was founded on April 23,1970, by Alvin B, phillips, a Motorola employee, as General Digital, initially a manufacturer of MOS test equipment. It rapidly became a speciality semiconductor maker, with capital provided by several individual investors. Around July 1971, it adopted its current name and soon introduced its first product, the oil crisis of the mid-1970s and the bankruptcy of its biggest calculator customer, Bowmar Instrument, changed its fortunes, however, and in 1976 Western Digital declared Chapter 11 bankruptcy. After this, Emerson withdrew their support of the company, WDC introduced several landmark products during this time, including the MCP-1600 multi-chip, microcoded CPU. The MCP-1600 was used to implement DECs LSI-11 system and their own Pascal MicroEngine microcomputer which ran the UCSD p-System Version III, the processor was also used in several single-chip floppy disk drive controller chips, notably the FD1771. However, the WD integrated circuit that arguably drove Westerns forward integration was the 1771 chip, despite a price far higher than average CMOS chips of the time, it was very successful and extremely profitable. That controller, the WD1003, became the basis of the ATA interface, throughout most of the 1980s, the family of controllers based on the WD1003 provided the bulk of WDCs revenues and profits, and for a time generated enormous corporate growth. Much of the mid-to-late 1980s saw an effort by WDC to use the profits from their ATA storage controllers to become a general-purpose OEM hardware supplier for the PC industry, as a result, WDC purchased a number of hardware companies. These included graphics cards, core logic chipsets, SCSI controller chips for disk and tape devices and they did well, but storage-related chips and disk controllers were their biggest money makers. 1988 also brought what would be the biggest change in WDCs history and that year, WDC bought the hard drive production assets of PC hardware maker Tandon, the first products of that union under WDCs own name were the Centaur series of ATA and XT attachment drives. By 1991, things were starting to slow down, as the PC industry moved from ST-506 and ESDI drives to ATA and SCSI and that year saw the rise of WDCs Caviar drives, brand new designs that used the latest in embedded servo and computerized diagnostic systems. Eventually, the sales of the Caviar drives resulted in WDC starting to sell some of its divisions. Paradise was sold to Philips, and since disappeared and its networking and floppy drive controller divisions went to SMC Networks and its SCSI chip business went to Future Domain, which was later bought out by market leader Adaptec. Around 1995, the lead that the Caviar drives had enjoyed was eclipsed by newer offerings from other companies, especially Quantum Corp. Products and ideas of time did not go far. The Portfolio drive was a flop, as was the SDX hard disk to CD-ROM interface, in an attempt to turn the tide in 1998, WDC recruited the help of IBM
