Computer

A computer is a device or for processing information from data according to a program — a compiled list of instructions. The information to be processed may represent numbers, text, pictures, or sound, amongst many other types.

Digital circuits

The conceptual design above could be implemented using a variety of different technologies. As previously mentioned, a stored program computer could be designed entirely of mechanical components like Babbage's. However, digital circuits allow Boolean logic and arithmetic using binary numerals to be implemented using relays - essentially, electrically controlled switches. Shannon's famous thesis showed how relays could be arranged to form units called logic gates, implementing simple Boolean operations. Others soon figured out the vacuum tubes - electronic devices, could be used instead. Vacuum tubes were originally used as a signal amplifier for radio and other applications, but were used in digital electronics as a very fast switch; when electricity is provided to one of the pins, current can flow through between the other two.

Related Topics:
Digital circuits - Boolean logic - Arithmetic using binary numerals - Relays - Logic gates - Vacuum tubes - Amplifier

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Through arrangements of logic gates, one can build digital circuits to do more complex tasks, for instance, an adder, which implements in electronics the same method - in computer terminology, an algorithm - to add two numbers together that children are taught - add one column at a time, and carry what's left over. Eventually, through combining circuits together, a complete ALU and control system can be built up. This does require a considerable number of components. CSIRAC, one of the earliest stored-program computers, is probably close to the smallest practically useful design. It had about 2,000 valves, Some of which were "dual components", so this represented somewhere between 2 and 4,000 logic components.

Related Topics:
Adder - Algorithm - CSIRAC

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Vacuum tubes had severe limitations for the construction of large numbers of gates. They were expensive, unreliable (particularly when used in such large quantities), took up a lot of space, and used a lot of electrical power, and, while incredibly fast compared to a mechanical switch, had limits to the speed at which they could operate. Therefore, by the 1960s they were replaced by the transistor, a new device which performed the same task as the tube but was much smaller, faster operating, reliable, used much less power, and was far cheaper.

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In the 1960s and 1970s, the transistor itself was gradually replaced by the integrated circuit, which placed multiple transistors (and other components) and the wires connecting them on a single, solid piece of silicon. By the 1970s, the entire ALU and control unit, the combination becoming known as a CPU, were being placed on a single "chip" called a microprocessor. Over the history of the integrated circuit, the number of components that can be placed on one has grown enormously. The first IC's contained a few tens of components; as of 2005, modern microprocessors such from AMD and Intel contain over 100 million transistors.

Related Topics:
Integrated circuit - CPU - Microprocessor - AMD - Intel

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Tubes, transistors, and transistors on integrated circuits can be and are used as the "storage" component of the stored-program architecture, using a circuit design known as a flip-flop, and indeed flip-flops are used for small amounts of very high-speed storage. However, few computer designs have used flip-flops for the bulk of their storage needs. Instead, earliest computers stored data in Williams tubes - essentially, projecting some dots on a TV screen and reading them again, or mercury delay lines where the data was stored as sound pulses travelling slowly (compared to the machine itself) along long tubes filled with mercury. These somewhat ungainly but effective methods were eventually replaced by magnetic memory devices, such as magnetic core memory, where electrical currents were used to introduce a permanent (but weak) magnetic field in some ferrous material, which could then be read to retrieve the data. Eventually, DRAM was introduced. A DRAM unit is a type of integrated circuit containing huge banks of an electronic component called a capacitor which can store an electrical charge for a period of time. The level of charge in a capacitor could be set to store information, and then measured to read the information when required.

Related Topics:
Flip-flop - Williams tube - Mercury delay line - Magnetic core memory - DRAM - Capacitor

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I/O devices

I/O is a general term for the devices by which a computer is sent information from the outside world, including instructions on what it is to do, and how it sends back the results of its computations; these can either be for the purpose of viewing by people, or perhaps for the purposes of controlling other machines; in a robot, for instance, the controlling computer's major output device is the robot itself.

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The first generation of computers were typically equipped with a fairly limited range of input devices; a punch card reader or something similar was used to input instructions and data into the computers memory, and some kind of printer, usually a modified teletype, was used to record the results. Over the years, though, a huge variety of other devices have been added. For the personal computer, for instance, Keyboards, and mice, are the primary ways people directly enter information into the computer, and monitors are a major way information from the computer is presented back to the computer user, though printers and some kind of sound-generating device are also very commonly used. There are a huge variety of other devices for obtaining other types of input; one example is the digital camera, which can be used to input visual information. Two of the most prominent classes of I/O device are secondary storage devices such as hard disks, CD-ROMs, key drives and the like; these represent comparatively slow, but high-capacity devices where information can be stored for later retrieval. Second is devices to access computer networks; the ability to transfer data between computers has opened up a huge range of capabilities for the computer. Collectively, the global Internet lets millions of computers transfer information of all types between each other.

Related Topics:
Punch card - Teletype - Keyboard - Mice - Monitor - Digital camera - Secondary storage - Hard disk - CD-ROM - Key drives - Computer network - Internet

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Instructions

The instructions interpreted by the control unit, and executed by the ALU, are not nearly as rich as a human language. A computer only has a limited number of well-defined, simple instructions, but they are not ambiguous. Typical sorts of instructions supported by most computers are "copy the contents of memory cell 5 and place the copy in cell 10", "add the contents of cell 7 to the contents of cell 13 and place the result in cell 20", "if the contents of cell 999 are 0, the next instruction is at cell 30". All computer instructions fall into one of four categories: 1) moving data from one location to another; 2) executing arithmetic and logical processes on data; 3) testing the condition of data; and 4) altering the sequence of operations.

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Instructions are represented within the computer as binary code - a base two system of counting. For example, the code for one kind of "copy" operation in the Intel line of microprocessors is 10110000. The particular instruction set that a specific computer supports is known as that computer's machine language.

Related Topics:
Binary - Machine language

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To slightly oversimplify, if two computers have CPUs share the same set of instructions, software from one can run on the other without modification. This easy portability of existing software creates a great incentive to stick with existing designs, only switching for the most compelling of reasons, and has gradually narrowed the number of distinct instruction set architectures in the marketplace.

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Programs

Computer programs are simply lists of instructions for the computer to execute. This can range from just a few instructions which perform a simple task, to a much more complex instruction list which may also include tables of data. Many computer programs contain millions of instructions, and many of those instructions are executed repeatedly. A typical modern PC (in the year 2005) can execute around 3 billion instructions per second. Computers do not gain their extraordinary capabilities through the ability to execute complex instructions. Rather, they do millions of simple instructions arranged by people known as "programmers."

Related Topics:
Computer program - PC - 2005 - Programmer

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In practice, people do not normally write the instructions for computers directly in machine language. Such programming is incredibly tedious and highly error-prone, making programmers very unproductive. Instead, programmers describe the desired actions in a "high level" programming language which is then translated into the machine language automatically by special computer programs (interpreters and compilers). Some programming languages map very closely to the machine language, such as Assembly Language (low level languages); at the other end, languages like Prolog are based on abstract principles far removed from the details of the machine's actual operation (high level languages). The language chosen for a particular task depends on the nature of the task, the skillset of the programmers, tool availability and, often, the requirements of the customers (for instance, projects for the US military were often required to be in the Ada programming language).

Related Topics:
Programming language - Interpreter - Compiler - Assembly Language - Prolog - Ada programming language

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Computer software is an alternative term for computer programs; it is a more inclusive phrase and includes all the ancillary material accompanying the program needed to do useful tasks. For instance, a video game includes not only the program itself, but data representing the pictures, sounds, and other material needed to create the virtual environment of the game. A computer application is a piece of computer software provided to many computer users, often in a retail environment. The stereotypical modern example of an application is perhaps the office suite, a set of interrelated programs for performing common office tasks.

Related Topics:
Computer software - Video game - Computer application - Office suite

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Going from the extremely simple capabilities of a single machine language instruction to the myriad capabilities of application programs means that many computer programs are extremely large and complex. A typical example is the Firefox web browser, created from roughly 2 million lines of computer code in the C++ programming language; there are many projects of even bigger scope, built by large teams of programmers. The management of this enormous complexity is key to making such projects possible; programming languages, and programming practices, enable the task to be divided into smaller and smaller subtasks until they come within the capabilities of a single programmer in a reasonable period.

Related Topics:
Firefox web browser - C++ - Programming language

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Nevertheless, the process of developing software remains slow, unpredictable, and error-prone; the discipline of software engineering has attempted, with some partial success, to make the process quicker and more productive and improve the quality of the end product.

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Libraries and operating systems

Soon after the development of the computer, it was discovered that certain tasks were required in many different programs; an early example was computing some of the standard mathematical functions. For the purposes of efficiency, standard versions of these were collected in libraries and made available to all who required them. A particularly common task set related to handling the gritty details of "talking" to the various I/O devices, so libraries for these were quickly developed.

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By the 1960's, with computers in wide industrial use for many purposes, it became common for them to be used for many different jobs within an organization. Soon, special software to automate the scheduling and execution of these many jobs became available. The combination of managing "hardware" and scheduling jobs became known as the "operating system"; the classic example of this type of early operating system was OS/360 by IBM.

Related Topics:
OS/360 - IBM

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The next major development in operating systems was timesharing - the idea that multiple users could use the machine "simultaneously" by keeping all of their programs in memory, executing each user's program for a short time so as to provide the illusion that each user had their own computer. Such a development required the operating system to provide each user's programs with a "virtual machine" such that one user's program could not interfere with another's (by accident or design). The range of devices that operating systems had to manage also expanded; a notable one was hard disks; the idea of individual "files" and a hierachical structure of "directories" (now often called folders) greatly simplified the use of these devices for permanent storage. System of security allowing computer users access only to files, directories and programs they had permissions to use were also common.

Related Topics:
Timesharing - Hard disk

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Perhaps the last major addition to the operating system were tools to provide programs with a standardised graphical user interface. While there are few technical reasons why a GUI has to be tied to the rest of an operating system, it allows the operating system vendor to encourage all the software for their operating system to have a similar looking and acting interface.

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Outside these "core" functions, operating systems are usually shipped with an array of other tools, some of which may have little connection with these original core functions but have been found useful by enough customers for a provider to include them. For instance, Apple OS X ships with a digital video editor application.

Related Topics:
Apple OS X - Digital video editor

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Not all operating systems provide all of the above functions; operating systems for smaller computers typically provide fewer, such as the highly minimal operating systems for early microcomputers. Embedded computers may have a specialised operating system, or sometimes none at all. Instead the custom programs written for their task perform all necessary functions that would be performed by an operating system in less specialised roles.

Related Topics:
Microcomputer - Embedded computer

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