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 hardware components and software, including communication protocols. Early computer buses were parallel electrical wires with multiple hardware connections, but the term is now used for any physical arrangement that provides the same logical function as a parallel electrical bus. Modern computer buses can use both parallel and bit serial connections, can be wired in either a multidrop or daisy chain topology, or connected by switched hubs, as in the case of USB. Computer systems consist of three main parts: the central processing unit that processes data, memory that holds the programs and data to be processed, I/O devices as peripherals that communicate with the outside world. An early computer might contain a hand-wired CPU of vacuum tubes, a magnetic drum for main memory, a punch tape and printer for reading and writing data respectively.
A modern system might have a multi-core CPU, DDR4 SDRAM for memory, a solid-state drive for secondary storage, a graphics card and LCD as a display system, a mouse and keyboard for interaction, a Wi-Fi connection for networking. 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 coupled. A microprocessor conventionally is a single chip which has a number of electrical connections on its pins that can be used to select an "address" in the main memory and another set of pins to read and write the data stored at that location. In most cases, the CPU and memory share signalling operate in synchrony; the bus connecting the CPU and memory is one of the defining characteristics of the system, referred to as the system bus. It is possible to allow peripherals to communicate with memory in the same fashion, attaching adaptors in the form of expansion cards directly to the system bus.
This is accomplished through some sort of standardized electrical connector, several of these forming the expansion bus or local bus. However, as the performance differences between the CPU and peripherals varies some solution is needed to ensure that peripherals do not slow overall system performance. Many CPUs feature a second set of pins similar to those for communicating with memory, but able to operate at different speeds and using different protocols. Others use smart controllers to place the data directly in memory, a concept known as direct memory access. Most modern systems combine both solutions; as the number of potential peripherals grew, using an expansion card for every peripheral became untenable. This has led to the introduction of bus systems designed 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 high-performance systems are too expensive to implement in low-end devices, like a mouse.
This has led to the parallel development of a number of low-performance bus systems for these solutions, the most common example being the standardized Universal Serial Bus. 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. In such systems, CPUs communicate using high-performance buses that operate at speeds much greater than memory, communicate with memory using protocols similar to those used for peripherals in the past; these system buses are used to communicate with most other peripherals, through adaptors, which in turn talk to other peripherals and controllers. Such systems are architecturally more similar to multicomputers, communicating over a bus rather than a network. In these cases, expansion buses are separate and no longer share any architecture with their host CPU.
What would have been a system bus is now known as a front-side bus. Given these changes, the classical terms "system", "expansion" and "peripheral" no longer have the same connotations. Other common categorization systems are based on the bus's primary role, connecting devices internally or externally, PCI vs. SCSI for instance. However, many common modern bus systems can be used for both. Other examples, like InfiniBand and I²C were designed from the start to be used both internally and externally; the internal bus known as internal data bus, memory bus, system bus or Front-Side-Bus, connects all the internal components of a computer, such as CPU and memory, to the motherboard. Internal data buses are referred to as a local bus, because they are intended to connect to local devices; this bus is rather quick and is independent of the rest of the computer operations. The external bus, or expansion bus, is made up of the electronic pathways that connect the different external devices, such as printer etc. to the computer.
Buses can be parallel buses, which carry data words in parallel on multiple wires, or serial buses, which carry data in bit-serial form. The addition of extra power and control connections, differential
NeXT Computer
NeXT Computer is a workstation computer sold by NeXT Inc., introduced in October 1988. Sold at a price of US$6,500 it was aimed at the higher-education market. Designed around the Motorola's 68030 CPU and 68882 floating-point coprocessor, it has a clock speed of 25 MHz, it runs the Mach and BSD-derived Unix based NeXTSTEP operating system with a proprietary GUI using a Display PostScript-based back end. The NeXT Computer enclosure consists of a 1-foot die-cast magnesium cube-shaped black case, which led to the machine being informally referred to as "The Cube"; the NeXT Computer was succeeded by the NeXTcube, an upgraded model in 1990. The NeXT Computer was launched in October 1988 at a lavish invitation-only event, "NeXT Introduction – the Introduction to the NeXT Generation of Computers for Education" at the Louise M. Davies Symphony Hall in San Francisco, California; the next day, selected educators and software developers were invited to attend—for a $100 registration fee—the first public technical overview of the NeXT computer at an event called "The NeXT Day" at the San Francisco Hilton.
It gave those interested in developing NeXT software an insight into the system's software architecture and object-oriented programming. Steve Jobs was the luncheon's speaker. In 1989, BYTE Magazine listed the NeXT Computer among the "Excellence" winners of the BYTE Awards, stating that it showed "what can be done when a personal computer is designed as a system, not a collection of hardware elements". Citing as "truly innovative" the optical drive, DSP and object-oriented programming environment, it concluded that "the NeXT Computer is worth every penny of its $6,500 market price", it was, not a significant commercial success, failing to reach the level of high-volume sales like the Apple II, Commodore 64, the Macintosh, or Microsoft Windows PCs. The workstations were sold to universities, financial institutions, government agencies. A NeXT Computer and its object oriented development tools and libraries were used by Tim Berners-Lee and Robert Cailliau at CERN to develop the world's first web server software, CERN httpd, used to write the first web browser, WorldWideWeb.
The NeXT Computer and the same object oriented development tools and libraries were used by Jesse Tayler at Paget Press to develop the first electronic app store, the Electronic AppWrapper in the early 1990s. Issue #3 was first demonstrated to Steve Jobs at NeXTWorld Expo 1993. Pioneering PC games Doom, Doom II, Quake were developed by id Software on NeXT machines. Other games based on the Doom engine such as Heretic and its sequel Hexen by Raven Software as well as Strife by Rogue Entertainment were developed on NeXT hardware using id's tools. Previous, emulator of NeXT hardware NeXTstation NeXTcube NeXTcube Turbo NeXT character set Byte Magazine, November 1988: The NeXT Computer Facsimile, Full text Simson Garfinkel's NeXT pages including NeXTWorld Magazine The Best of NeXT Collection NeXT Computer brochure old-computers.com — NeXTcube Photos of black hardware
Embedded system
An embedded system is a controller programmed and controlled by a real-time operating system with a dedicated function within a larger mechanical or electrical system with real-time computing constraints. It is embedded as part of a complete device including hardware and mechanical parts. Embedded systems control many devices in common use today. Ninety-eight percent of all microprocessors manufactured are used in embedded systems. Examples of properties of typical embedded computers when compared with general-purpose counterparts are low power consumption, small size, rugged operating ranges, low per-unit cost; this comes at the price of limited processing resources, which make them more difficult to program and to interact with. However, by building intelligence mechanisms on top of the hardware, taking advantage of possible existing sensors and the existence of a network of embedded units, one can both optimally manage available resources at the unit and network levels as well as provide augmented functions, well beyond those available.
For example, intelligent techniques can be designed to manage power consumption of embedded systems. Modern embedded systems are based on microcontrollers, but ordinary microprocessors are common in more complex systems. In either case, the processor used may be types ranging from general purpose to those specialized in certain class of computations, or custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor. Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance; some embedded systems are mass-produced. Embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, complex systems like hybrid vehicles, MRI, avionics. Complexity varies from low, with a single microcontroller chip, to high with multiple units and networks mounted inside a large chassis or enclosure.
One of the first recognizably modern embedded systems was the Apollo Guidance Computer, developed ca. 1965 by Charles Stark Draper at the MIT Instrumentation Laboratory. At the project's inception, the Apollo guidance computer was considered the riskiest item in the Apollo project as it employed the newly developed monolithic integrated circuits to reduce the size and weight. An early mass-produced embedded system was the Autonetics D-17 guidance computer for the Minuteman missile, released in 1961; when the Minuteman II went into production in 1966, the D-17 was replaced with a new computer, the first high-volume use of integrated circuits. Since these early applications in the 1960s, embedded systems have come down in price and there has been a dramatic rise in processing power and functionality. An early microprocessor for example, the Intel 4004, was designed for calculators and other small systems but still required external memory and support chips. In 1978 National Engineering Manufacturers Association released a "standard" for programmable microcontrollers, including any computer-based controllers, such as single board computers and event-based controllers.
As the cost of microprocessors and microcontrollers fell it became feasible to replace expensive knob-based analog components such as potentiometers and variable capacitors with up/down buttons or knobs read out by a microprocessor in consumer products. By the early 1980s, memory and output system components had been integrated into the same chip as the processor forming a microcontroller. Microcontrollers find applications. A comparatively low-cost microcontroller may be programmed to fulfill the same role as a large number of separate components. Although in this context an embedded system is more complex than a traditional solution, most of the complexity is contained within the microcontroller itself. Few additional components may be needed and most of the design effort is in the software. Software prototype and test can be quicker compared with the design and construction of a new circuit not using an embedded processor. Embedded systems are found in consumer, automotive, medical and military applications.
Telecommunications systems employ numerous embedded systems from telephone switches for the network to cell phones at the end user. Computer networking uses dedicated routers and network bridges to route data. Consumer electronics include MP3 players, mobile phones, video game consoles, digital cameras, GPS receivers, printers. Household appliances, such as microwave ovens, washing machines and dishwashers, include embedded systems to provide flexibility and features. Advanced HVAC systems use networked thermostats to more and efficiently control temperature that can change by time of day and season. Home automation uses wired- and wireless-networking that can be used to control lights, security, audio/visual, etc. all of which use embedded devices for sensing and controlling. Transportation systems from flight to automobiles use embedded systems. New airplanes contain advanced avionics such as inertial guidance systems and GPS receivers that have considerable safety requirements. Various electric motors — brushless DC motors, induction motors and DC motors — use electric/electronic motor controllers.
Automobiles, electric vehicles, hy
Motorola
Motorola, Inc. was an American multinational telecommunications company founded on September 25, 1928, based in Schaumburg, Illinois. After having lost $4.3 billion from 2007 to 2009, the company was divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011. Motorola Solutions is considered to be the direct successor to Motorola, as the reorganization was structured with Motorola Mobility being spun off. Motorola Mobility was sold to Google in 2012, acquired by Lenovo in 2014. Motorola designed and sold wireless network equipment such as cellular transmission base stations and signal amplifiers. Motorola's home and broadcast network products included set-top boxes, digital video recorders, network equipment used to enable video broadcasting, computer telephony, high-definition television, its business and government customers consisted of wireless voice and broadband systems, public safety communications systems like Astro and Dimetra. These businesses are now part of Motorola Solutions.
Google sold Motorola Home to the Arris Group in December 2012 for US$2.35 billion. Motorola's wireless telephone handset division was a pioneer in cellular telephones. Known as the Personal Communication Sector prior to 2004, it pioneered the "mobile phone" with DynaTAC, "flip phone" with the MicroTAC, as well as the "clam phone" with the StarTAC in the mid-1990s, it had staged a resurgence by the mid-2000s with the Razr, but lost market share in the second half of that decade. It focused on smartphones using Google's open-source Android mobile operating system; the first phone to use the newest version of Google's open source OS, Android 2.0, was released on November 2, 2009 as the Motorola Droid. The handset division was spun off into the independent Motorola Mobility. On May 22, 2012, Google CEO Larry Page announced that Google had closed on its deal to acquire Motorola Mobility. On January 29, 2014, Page announced that, pending closure of the deal, Motorola Mobility would be acquired by Chinese technology company Lenovo for US$2.91 billion.
On October 30, 2014, Lenovo finalized its purchase of Motorola Mobility from Google. Motorola started in Chicago, Illinois, as Galvin Manufacturing Corporation in 1928 when brothers Paul V. and Joseph E. Galvin purchased the bankrupt Stewart Battery Company's battery-eliminator plans and manufacturing equipment at auction for $750. Galvin Manufacturing Corporation set up shop in a small section of a rented building; the company had $565 in five employees. The first week's payroll was $63; the company's first products were the battery eliminators, devices that enabled battery-powered radios to operate on household electricity. Due to advances in radio technology, battery-eliminators soon became obsolete. Paul Galvin learned that some radio technicians were installing sets in cars, challenged his engineers to design an inexpensive car radio that could be installed in most vehicles, his team was successful, Galvin was able to demonstrate a working model of the radio at the June 1930 Radio Manufacturers Association convention in Atlantic City, New Jersey.
He brought home enough orders to keep the company in business. Paul Galvin wanted a brand name for Galvin Manufacturing Corporation's new car radio, created the name “Motorola” by linking "motor" with "ola", a popular ending for many companies at the time, e.g. Moviola, Crayola; the company sold its first Motorola branded radio on June 23, 1930, to Herbert C. Wall of Fort Wayne, for $30. Wall went on to become one of the first Motorola distributors in the country; the Motorola brand name became so well known that Galvin Manufacturing Corporation changed its name to Motorola, Inc. Galvin Manufacturing Corporation began selling Motorola car-radio receivers to police departments and municipalities in November 1930; the company's first public safety customers included the Village of River Forest, Village of Bellwood Police Department, City of Evanston Police, Illinois State Highway Police, Cook County Police with a one-way radio communication. In the same year, the company built its research and development program with Dan Noble, a pioneer in FM radio and semiconductor technologies, who joined the company as director of research.
The company produced the hand-held AM SCR-536 radio during World War II, vital to Allied communication. Motorola ranked 94th among United States corporations in the value of World War II military production contracts. Motorola went public in 1943, became Motorola, Inc. in 1947. At that time Motorola's main business was selling televisions and radios. In October 1946 Motorola communications equipment carried the first calls on Illinois Bell telephone company's new car radiotelephone service in Chicago; the company began making televisions in 1947, with the model VT-71 with 7-inch cathode ray tube. In 1952, Motorola opened its first international subsidiary in Toronto, Canada to produce radios and televisions. In 1953, the company established the Motorola Foundation to support leading universities in the United States. In 1955, years after Motorola started its research and development laboratory in Phoenix, Arizona, to research new solid-state technology, Motorola introduced the world's first commercial high-power germanium-based transistor.
The pr
Digital signal processor
A digital signal processor is a specialized microprocessor, with its architecture optimized for the operational needs of digital signal processing. The goal of DSP is to measure, filter or compress continuous real-world analog signals. Most general-purpose microprocessors can execute digital signal processing algorithms but may not be able to keep up with such processing continuously in real-time. Dedicated DSPs have better power efficiency, thus they are more suitable in portable devices such as mobile phones because of power consumption constraints. DSPs use special memory architectures that are able to fetch multiple data or instructions at the same time. Digital signal processing algorithms require a large number of mathematical operations to be performed and on a series of data samples. Signals are converted from analog to digital, manipulated digitally, converted back to analog form. Many DSP applications have constraints on latency. Most general-purpose microprocessors and operating systems can execute DSP algorithms but are not suitable for use in portable devices such as mobile phones and PDAs because of power efficiency constraints.
A specialized digital signal processor, will tend to provide a lower-cost solution, with better performance, lower latency, no requirements for specialised cooling or large batteries. Such performance improvements have led to the introduction of digital signal processing in commercial communications satellites where hundreds or thousands of analog filters, frequency converters and so on are required to receive and process the uplinked signals and ready them for downlinking, can be replaced with specialised DSPs with a significant benefits to the satellites' weight, power consumption, complexity/cost of construction and flexibility of operation. For example, the SES-12 and SES-14 satellites from operator SES, both intended for launch in 2017, were built by Airbus Defence and Space with 25% of capacity using DSP; the architecture of a digital signal processor is optimized for digital signal processing. Most support some of the features as an applications processor or microcontroller, since signal processing is the only task of a system.
Some useful features for optimizing DSP algorithms are outlined below. By the standards of general-purpose processors, DSP instruction sets are highly irregular. Both traditional and DSP-optimized instruction sets are able to compute any arbitrary operation but an operation that might require multiple ARM or x86 instructions to compute might require only one instruction in a DSP optimized instruction set. One implication for software architecture is that hand-optimized assembly-code routines are packaged into libraries for re-use, instead of relying on advanced compiler technologies to handle essential algorithms. With modern compiler optimizations hand-optimized assembly code is more efficient and many common algorithms involved in DSP calculations are hand-written in order to take full advantage of the architectural optimizations. Multiply–accumulates operations used extensively in all kinds of matrix operations convolution for filtering dot product polynomial evaluation Fundamental DSP algorithms depend on multiply–accumulate performance FIR filters Fast Fourier transform Instructions to increase parallelism: SIMD VLIW superscalar architecture Specialized instructions for modulo addressing in ring buffers and bit-reversed addressing mode for FFT cross-referencing Digital signal processors sometimes use time-stationary encoding to simplify hardware and increase coding efficiency.
Multiple arithmetic units may require memory architectures to support several accesses per instruction cycle Special loop controls, such as architectural support for executing a few instruction words in a tight loop without overhead for instruction fetches or exit testing Saturation arithmetic, in which operations that produce overflows will accumulate at the maximum values that the register can hold rather than wrapping around. Sometimes various sticky bits operation modes are available. Fixed-point arithmetic is used to speed up arithmetic processing Single-cycle operations to increase the benefits of pipelining Floating-point unit integrated directly into the datapath Pipelined architecture Highly parallel multiplier–accumulators Hardware-controlled looping, to reduce or eliminate the overhead required for looping operations In engineering, hardware architecture refers to the identification of a system's physical components and their interrelationships; this description called a hardware design model, allows hardware designers to understand how their components fit into a system architecture and provides to software component designers important information needed for software development and integration.
Clear definition of a hardware architecture allows the various traditional engineering disciplines to work more together to develop and manufacture new machines and components. Hardware is als
Workstation
A workstation is a special computer designed for technical or scientific applications. Intended to be used by one person at a time, they are connected to a local area network and run multi-user operating systems; the term workstation has been used loosely to refer to everything from a mainframe computer terminal to a PC connected to a network, but the most common form refers to the group of hardware offered by several current and defunct companies such as Sun Microsystems, Silicon Graphics, Apollo Computer, DEC, HP, NeXT and IBM which opened the door for the 3D graphics animation revolution of the late 1990s. Workstations offered higher performance than mainstream personal computers with respect to CPU and graphics, memory capacity, multitasking capability. Workstations were optimized for the visualization and manipulation of different types of complex data such as 3D mechanical design, engineering simulation and rendering of images, mathematical plots; the form factor is that of a desktop computer, consist of a high resolution display, a keyboard and a mouse at a minimum, but offer multiple displays, graphics tablets, 3D mice, etc.
Workstations were the first segment of the computer market to present advanced accessories and collaboration tools. The increasing capabilities of mainstream PCs in the late 1990s have blurred the lines somewhat with technical/scientific workstations; the workstation market employed proprietary hardware which made them distinct from PCs. However, by the early 2000s this difference disappeared, as workstations now use commoditized hardware dominated by large PC vendors, such as Dell, Hewlett-Packard and Fujitsu, selling Microsoft Windows or Linux systems running on x86-64 processors; the first computer that might qualify as a "workstation" was the IBM 1620, a small scientific computer designed to be used interactively by a single person sitting at the console. It was introduced in 1960. One peculiar feature of the machine was. To perform addition, it required a memory-resident table of decimal addition rules; this saved on the cost of logic circuitry. The machine was code-named CADET and rented for $1000 a month.
In 1965, IBM introduced the IBM 1130 scientific computer, meant as the successor to the 1620. Both of these systems came with the ability to run programs written in other languages. Both the 1620 and the 1130 were built into desk-sized cabinets. Both were available with add-on disk drives and both paper-tape and punched-card I/O. A console typewriter for direct interaction was standard on each. Early examples of workstations were dedicated minicomputers. A notable example was the PDP-8 from Digital Equipment Corporation, regarded to be the first commercial minicomputer; the Lisp machines developed at MIT in the early 1970s pioneered some of the principles of the workstation computer, as they were high-performance, single-user systems intended for interactive use. Lisp Machines were commercialized beginning 1980 by companies like Symbolics, Lisp Machines, Texas Instruments and Xerox; the first computer designed for single-users, with high-resolution graphics facilities was the Xerox Alto developed at Xerox PARC in 1973.
Other early workstations include the Terak 8510/a, Three Rivers PERQ and the Xerox Star. In the early 1980s, with the advent of 32-bit microprocessors such as the Motorola 68000, a number of new participants in this field appeared, including Apollo Computer and Sun Microsystems, who created Unix-based workstations based on this processor. Meanwhile, DARPA's VLSI Project created several spinoff graphics products as well, notably the SGI 3130, Silicon Graphics' range of machines that followed, it was not uncommon to differentiate the target market for the products, with Sun and Apollo considered to be network workstations, while the SGI machines were graphics workstations. As RISC microprocessors became available in the mid-1980s, these were adopted by many workstation vendors. Workstations tended to be expensive several times the cost of a standard PC and sometimes costing as much as a new car. However, minicomputers sometimes cost as much as a house; the high expense came from using costlier components that ran faster than those found at the local computer store, as well as the inclusion of features not found in PCs of the time, such as high-speed networking and sophisticated graphics.
Workstation manufacturers tend to take a "balanced" approach to system design, making certain to avoid bottlenecks so that data can flow unimpeded between the many different subsystems within a computer. Additionally, given their more specialized nature, tend to have higher profit margins than commodity-driven PCs; the systems that come out of workstation companies feature SCSI or Fibre Channel disk storage systems, high-end 3D accelerators, single or multiple 64-bit processors, large amounts of RAM, well-designed cooling. Additionally, the companies that make the products tend to have good repair/replacement plans. However, the line between workstation and PC is becoming blurred as the demand for fast computers and graphics have become
Accumulator (computing)
In a computer's central processing unit, the accumulator is a register in which intermediate arithmetic and logic results are stored. Without a register like an accumulator, it would be necessary to write the result of each calculation to main memory only to be read right back again for use in the next operation. Access to main memory is slower than access to a register like the accumulator because the technology used for the large main memory is slower than that used for a register. Early electronic computer systems were split into two groups, those with accumulators and those without. Modern computer systems have multiple general purpose registers that operate as accumulators, the term is no longer as common as it once was. However, a number of special-purpose processors still use a single accumulator for their work to simplify their design. Mathematical operations take place in a stepwise fashion, using the results from one operation as the input to the next. For instance, a manual calculation of a worker's weekly payroll might look something like: look up the number of hours worked from the employee's time card look up the pay rate for that employee from a table multiply the hours by the pay rate to get their basic weekly pay multiply their basic pay by a fixed percentage to account for income tax subtract that number from their basic pay to get their weekly pay after tax multiply that result by another fixed percentage to account for retirement plans subtract that number from their basic pay to get their weekly pay after all deductionsA computer program carrying out the same task would follow the same basic sequence of operations, although the values being looked up would all be stored in computer memory.
In early computers the number of hours would be held on a punch card and the pay rate in some other form of memory a magnetic drum. Once the multiplication is complete, the result needs to be placed somewhere. On a "drum machine" this would be back to the drum, an operation that takes considerable time, and the next operation has to read that value back in, which introduces another considerable delay. Accumulators improve performance in systems like these by providing a scratchpad area where the results of one operation can be fed to the next one for little or no performance penalty. In the example above, the basic weekly pay would be calculated and placed in the accumulator, which could immediately be used by the income tax calculation; this removes one save and one read operation from the sequence, operations that took tens to hundreds of times as long as the multiplication itself. An accumulator machine called a 1-operand machine, or a CPU with accumulator-based architecture, is a kind of CPU where, although it may have several registers, the CPU stores the results of calculations in one special register called "the accumulator".
All early computers were accumulator machines with only the high-performance "supercomputers" having multiple registers. As mainframe systems gave way to microcomputers, accumulator architectures were again popular with the MOS 6502 being a notable example. Many 8-bit microcontrollers that are still popular as of 2014, such as the PICmicro and 8051, are accumulator-based machines. Modern CPUs are 2-operand or 3-operand machines; the additional operands specify which one of many general purpose registers are used as the source and destination for calculations. These CPUs are not considered "accumulator machines"; the characteristic which distinguishes one register as being the accumulator of a computer architecture is that the accumulator would be used as an implicit operand for arithmetic instructions. For instance, a CPU might have an instruction like: ADD memaddress that adds the value read from memory location memaddress to the value in the accumulator, placing the result back in the accumulator.
The accumulator is not identified in the instruction by a register number. Some architectures use a particular register as an accumulator in some instructions, but other instructions use register numbers for explicit operand specification. Any system that uses a single "memory" to store the result of multiple operations can be considered an accumulator. J. Presper Eckert refers to the earliest adding machines of Gottfried Leibniz and Blaise Pascal as accumulator-based systems. Historical convention dedicates a register to "the accumulator", an "arithmetic organ" that accumulates its number during a sequence of arithmetic operations: "The first part of our arithmetic organ... should be a parallel storage organ which can receive a number and add it to the one in it, able to clear its contents and which can store what it contains. We will call such an organ an Accumulator, it is quite conventional in principle in past and present computing machines of the most varied types, e.g. desk multipliers, standard IBM counters, more modern relay machines, the ENIAC".
Just a few of the instructions are, for example: Clear accumulator and add number from memory location X Clear accumulator and subtract number from memory location X Add number copied from memory location X to the contents of the accumulator Subtract number copied from memory location X from the contents of the accumulator Clear accumulator and shift contents of register into accumulatorNo convention exists regarding the names for operations from registers to accumulator and from accumulator to registers
