Western Digital FD1771
The FD1771 is the first in a line of floppy disk controllers produced by Western Digital. It supports the IBM 3740 disk format, it is packaged in a 40-pin DIP. The FD1771 was succeeded by many derivatives that were software-compatible: The FD1781 was designed for double density, but required external modulation and demodulation circuitry, so it could support MFM, M2FM, GCR or other double-density encodings; the FD1791-FD1797 series added internal support for double density modulation, compatible with the IBM System/34 disk format. They required an external data separator; the WD1761-WD1767 series were versions of the FD179x series rated for a maximum clock frequency of 1 MHz, resulting in a data rate limit of 125 kbit/s for single density and 250 kbit/s for double density, thus preventing them from being used for 8-in floppy drives or the "high-density" 5.25-inch or 90 mm floppy drives. The WD2791-WD2797 series added an internal data separator using an analog phase-locked loop, with some external passive components required for the VCO.
They were intended for 8-inch and 5.25-inch drives. The WD1770, WD1772, WD1773 added an internal digital data separator and write precompensator, eliminating the need for external passive components but raising the clock rate requirement to 8 MHz, they supported double density, despite the apparent regression of the part number, were packaged in 28-pin DIP packages. The WD1772PH02-02 was a version of the chip that Atari fitted to the Atari STE which supported high density operation. After production at WD could not be sustained, Atari decided to license the design and modify it to get high density and extra density operation; the chip had the number C302096 and was produced by Toshiba. Many compatible chips were available from other vendors: FD179x series from SMC Microelectronics MB887x series from Fujitsu VL177x series from VLSI Technology. Soviet KR1818WG93 was a WD1793 analogThese families were used in many microcomputers and home computers including the Radio Shack TRS-80, Acorn Electron, BBC Master, Atari ST, Acorn Archimedes and the SAM Coupé, as well as the +D and DISCiPLE disk interfaces for the Sinclair ZX Spectrum, the Commodore 157x/1581 for the Commodore 64 and the Atari XF551 for the Atari XL/XE
Central processing unit
A central processing unit called a central processor or main processor, is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic and input/output operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s. Traditionally, the term "CPU" refers to a processor, more to its processing unit and control unit, distinguishing these core elements of a computer from external components such as main memory and I/O circuitry; the form and implementation of CPUs have changed over the course of their history, but their fundamental operation remains unchanged. Principal components of a CPU include the arithmetic logic unit that performs arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations and a control unit that orchestrates the fetching and execution of instructions by directing the coordinated operations of the ALU, registers and other components.
Most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit chip. An IC that contains a CPU may contain memory, peripheral interfaces, other components of a computer; some computers employ a multi-core processor, a single chip containing two or more CPUs called "cores". Array processors or vector processors have multiple processors that operate in parallel, with no unit considered central. There exists the concept of virtual CPUs which are an abstraction of dynamical aggregated computational resources. Early computers such as the ENIAC had to be physically rewired to perform different tasks, which caused these machines to be called "fixed-program computers". Since the term "CPU" is defined as a device for software execution, the earliest devices that could rightly be called CPUs came with the advent of the stored-program computer; the idea of a stored-program computer had been present in the design of J. Presper Eckert and John William Mauchly's ENIAC, but was 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. It was the outline of a stored-program computer that would be completed in August 1949. EDVAC was designed to perform a certain number of instructions of various types; the programs written for EDVAC were to be stored in high-speed computer memory rather than specified by the physical wiring of the computer. This overcame a severe limitation of ENIAC, the considerable time and effort required to reconfigure the computer to perform a new task. With von Neumann's design, the program that EDVAC ran could be changed by changing the contents of the memory. EDVAC, was not the first stored-program computer. Early CPUs were custom designs used as part of a sometimes distinctive computer. However, this method of designing custom CPUs for a particular application has 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 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, sometimes in toys. While von Neumann is most credited with the design of the stored-program computer because of his design of EDVAC, the design became known as the von Neumann architecture, others before him, such as Konrad Zuse, had suggested and implemented similar ideas; the so-called Harvard architecture of the Harvard Mark I, completed before EDVAC used a stored-program design using punched paper tape rather than electronic memory. The key difference between the von Neumann and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both.
Most modern CPUs are von Neumann in design, but CPUs with the Harvard architecture are seen as well in embedded applications. Relays and vacuum tubes were used as switching elements; 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 rarely. In the end, tube-based CPUs became dominant because the significant speed advantages afforded 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 common at this time, limited by the speed of the switching de
Commodore International was an American home computer and electronics manufacturer founded by Jack Tramiel. Commodore International, along with its subsidiary Commodore Business Machines, participated in the development of the home–personal computer industry in the 1970s and 1980s; the company developed and marketed the world's best-selling desktop computer, the Commodore 64, released its Amiga computer line in July 1985. With quarterly sales ending 1983 of $49 million, Commodore was one of the world's largest personal computer manufacturers; the company that would become Commodore Business Machines, Inc. was founded in 1954 in Toronto as the Commodore Portable Typewriter Company by Polish-Jewish immigrant and Auschwitz survivor Jack Tramiel. For a few years he had been living in New York, driving a taxicab, running a small business repairing typewriters, when he managed to sign a deal with a Czechoslovakian company to manufacture their designs in Canada, he moved to Toronto to start production.
By the late 1950s a wave of Japanese machines forced most North American typewriter companies to cease business, but Tramiel instead turned to adding machines. In 1955, the company was formally incorporated as Inc. in Canada. In 1962 Commodore went public on the New York Stock Exchange, under the name of Commodore International Limited. In the late 1960s, history repeated itself when Japanese firms started producing and exporting adding machines; the company's main investor and chairman, Irving Gould, suggested that Tramiel travel to Japan to understand how to compete. Instead, Tramiel returned with the new idea to produce electronic calculators, which were just coming on the market. Commodore soon had a profitable calculator line and was one of the more popular brands in the early 1970s, producing both consumer as well as scientific/programmable calculators. However, in 1975, Texas Instruments, the main supplier of calculator parts, entered the market directly and put out a line of machines priced at less than Commodore's cost for the parts.
Commodore obtained an infusion of cash from Gould, which Tramiel used beginning in 1976 to purchase several second-source chip suppliers, including MOS Technology, Inc. in order to assure his supply. He agreed to buy MOS, having troubles of its own, only on the condition that its chip designer Chuck Peddle join Commodore directly as head of engineering. Through the 1970s Commodore produced numerous peripherals and consumer electronic products such as the Chessmate, a chess computer based around a MOS 6504 chip, released in 1978. In December 2007, when Tramiel was visiting the Computer History Museum in Mountain View, for the 25th anniversary of the Commodore 64, he was asked why he called his company Commodore, he said: "I wanted to call my company General, but there's so many Generals in the U. S.: General Electric, General Motors. I went to Admiral, but, taken. So I wind up in Berlin, with my wife, we were in a cab, the cab made a short stop, in front of us was an Opel Commodore." Tramiel gave this account in many interviews, but Opel's Commodore didn't debut until 1967, years after the company had been named.
Once Chuck Peddle had taken over engineering at Commodore, he convinced Jack Tramiel that calculators were a dead end, that they should turn their attention to home computers. Peddle packaged his single-board computer design in a metal case with a keyboard using calculator keys with a full-travel QWERTY keyboard, monochrome monitor, tape recorder for program and data storage, to produce the Commodore PET. From PET's 1977 debut, Commodore would be a computer company. Commodore had been reorganized the year before into Commodore International, Ltd. moving its financial headquarters to the Bahamas and its operational headquarters to West Chester, near the MOS Technology site. The operational headquarters, where research and development of new products occurred, retained the name Commodore Business Machines, Inc. In 1980 Commodore launched production for the European market in Braunschweig. By 1980, Commodore was one of the three largest microcomputer companies, the largest in the Common Market.
The company had lost its early domestic-market sales leadership, however. BYTE stated of the business computer market that "the lack of a marketing strategy by Commodore, as well as its past nonchalant attitude toward the encouragement and development of good software, has hurt its credibility in comparison to the other systems on the market"; the author of Programming the PET/CBM stated in its introduction that "CBM's product manuals are recognized to be unhelpful. Commodore reemphasized the US market with the VIC-20; the PET computer line was used in schools, where its tough all-metal construction and ability to share printers and disk drives on a simple local area network were advantages, but PETs did not compete well in the home setting where graphics and sound were important. This was addressed with the VIC-20 in 1981, introduced at a cost of US$299 and sold in retail stores. Commodore bought aggressive advertisements featuring William Shatner asking consumers "Why buy just a video game?"
The strategy worked and the VIC-20 became the first computer to ship more than one million units. A total of 2.5 million units were sold over the machine's lifetime and helped Commodore's sales to Canadian schools. In another promotion aimed at schools (and as a
An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is executed directly by the hardware and makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers; the dominant desktop operating system is Microsoft Windows with a market share of around 82.74%. MacOS by Apple Inc. is in second place, the varieties of Linux are collectively in third place. In the mobile sector, use in 2017 is up to 70% of Google's Android and according to third quarter 2016 data, Android on smartphones is dominant with 87.5 percent and a growth rate 10.3 percent per year, followed by Apple's iOS with 12.1 percent and a per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent.
Linux distributions are dominant in supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency; this is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking.
32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources to multiple users. A distributed operating system manages a group of distinct computers and makes them appear to be a single computer; the development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine; when computers in a group work in cooperation, they form a distributed system.
In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, is common in large server warehouses. Embedded operating systems are designed to be used in embedded computer systems, they are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources, they are compact and efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.
A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their more complex forms until the early 1960s. Hardware features were added, that enabled use of runtime libraries and parallel processing; when personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems.
Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the pri
In telecommunications and signal processing, frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal. Digital data can be encoded and transmitted via FM by shifting the carrier's frequency among a predefined set of frequencies representing digits – for example one frequency can represent a binary 1 and a second can represent binary 0; this modulation technique is known as frequency-shift keying. FSK is used in modems such as fax modems, can be used to send Morse code. Radioteletype uses FSK. Frequency modulation is used for FM radio broadcasting, it is used in telemetry, seismic prospecting, monitoring newborns for seizures via EEG, two-way radio systems, music synthesis, magnetic tape-recording systems and some video-transmission systems.
In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation signal. For this reason, most music is broadcast over FM radio. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation; these methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. If the information to be transmitted is x m and the sinusoidal carrier is x c = A c cos , where fc is the carrier's base frequency, Ac is the carrier's amplitude, the modulator combines the carrier with the baseband data signal to get the transmitted signal: y = A c cos = A c cos = A c cos where f Δ = K f A m, K f being the sensitivity of the frequency modulator and A m being the amplitude of the modulating signal or baseband signal. In this equation, f is the instantaneous frequency of the oscillator and f Δ is the frequency deviation, which represents the maximum shift away from fc in one direction, assuming xm is limited to the range ±1.
While most of the energy of the signal is contained within fc ± fΔ, it can be shown by Fourier analysis that a wider range of frequencies is required to represent an FM signal. The frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are neglected in practical design problems. Mathematically, a baseband modulating signal may be approximated by a sinusoidal continuous wave signal with a frequency fm; this method is named as single-tone modulation. The integral of such a signal is: ∫ 0 t x m d τ = A m sin