Computer: Definition A computer is a machine that can be programmed to manipulate symbols. Its principal characteristics are: 1) It responds to a specific set of instructions in a well- defined manner. 2) It can execute a prerecorded list of instructions (a program). 3) It can quickly store and retrieve large amounts of data
Computer sizes and power Computers can be generally classified by size and power as follows, though there is considerable overlap: 1) Personal computer: A small, single-user computer based on a microprocessor. 2) Workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and, in general, a higher-quality monitor. 3) Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously. 4) Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously. 5) Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second
All general-purpose computers require the following hardware components: Central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions organized in programs ("software") which tell the computer what to do. Memory (fast, expensive, short-term memory): Enables a computer to store, at least temporarily, data, programs, and intermediate results. Mass storage device (slower, cheaper, long-term memory): Allows a computer to permanently retain large amounts of data and programs between jobs. Common mass storage devices include disk drives and tape drives. Input device: Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer. Output device: A display screen, printer, or other device that lets you see what the computer has accomplished
Supercomputer A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation. computer Supercomputers introduced in the 1960s were designed primarily by Seymour Cray at Control Data Corporation (CDC), and led the market into the 1970s until Cray left to form his own company, Cray Research. Seymour CrayControl Data CorporationCray Research Seymour CrayControl Data CorporationCray Research He then took over the supercomputer market with his new designs, holding the top spot in supercomputing for five years (1985–1990). In the 1980s a large number of smaller competitors entered the market, in parallel to the creation of the minicomputer market a decade earlier, but many of these disappeared in the mid-1990s "supercomputer market crash ". minicomputer
Supercomputer and Mainframe Supercomputer is a broad term for one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations (number crunching). For example, weather forecasting requires a supercomputer. Other uses of supercomputers scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting). Perhaps the best known supercomputer manufacturer is Cray Research.
Mainframe Mainframe was a term originally referring to the cabinet containing the central processor unit or "main frame" of a room-filling Stone Age batch machine. After the emergence of smaller "minicomputer" designs in the early 1970s, the traditional big iron machines were described as "mainframe computers" and eventually just as mainframes. Nowadays a Mainframe is a very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. But supercomputers can execute a single program faster than a mainframe. The distinction between small mainframes and minicomputers is vague, depending really on how the manufacturer wants to market its machines.
Common uses used for highly calculation-intensive tasks such as problems involving quantum mechanical physics, quantum mechanical physics quantum mechanical physics weather forecasting, weather forecasting weather forecasting climate research, physical simulations such as simulation of airplanes in wind tunnels, wind tunnelswind tunnels simulation of the detonation of nuclear weapons, and research into nuclear fusion,cryptanalysis, and many others. nuclear weaponsnuclear fusioncryptanalysisnuclear weaponsnuclear fusioncryptanalysis
Workstation It is a type of computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other types of applications that require a moderate amount of computing power and relatively high quality graphics capabilities. Workstations generally come with a large, high-resolution graphics screen, at large amount of RAM, built-in network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive. The most common operating systems for workstations are UNIX and Windows NT. Workstations are single-user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems. In networking, workstation refers to any computer connected to a local-area network. It could be a workstation or a personal computer.
Personal computer Personal computer: It can be defined as a small, relatively inexpensive computer designed for an individual user. In price, personal computers range anywhere from a few hundred pounds to over five thousand pounds. All are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is for playing games and recently for surfing the Internet.
Personal computers first appeared in the late 1970s. One of the first and most popular personal computers was the Apple II, introduced in 1977 by Apple Computer. During the late 1970s and early 1980s, new models and competing operating systems seemed to appear daily. Then, in 1981, IBM entered the fray with its first personal computer, known as the IBM PC. The IBM PC quickly became the personal computer of choice, and most other personal computer manufacturers fell by the wayside. P.C. is short for personal computer or IBM PC.
Personal Computer Types Actual personal computers can be generally classified by size and chassis / case. The chassis or case is the metal frame that serves as the structural support for electronic components. Every computer system requires at least one chassis to house the circuit boards and wiring. The chassis also contains slots for expansion boards. If you want to insert more boards than there are slots, you will need an expansion chassis, which provides additional slots. There are two basic flavors of chassis designs–desktop models and tower models–but there are many variations on these two basic types. Then come the portable computers that are computers small enough to carry. Portable computers include notebook and subnotebook computers, hand-held computers, palmtops, and PDAs.
Arithmetic Logic Unit In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. computingdigital circuitarithmetic logicalcomputingdigital circuitarithmetic logical The ALU is a fundamental building block of the central processing unit (CPU) of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers. central processing unitmicroprocessors central processing unitmicroprocessors The processors found inside modern CPUs and graphics processing units (GPUs) accommodate very powerful and very complex ALUs; a single component may contain a number of ALUs. GPUs
An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?"). boolean truth valuesboolean truth values
Logic operations Logic operations involve Boolean logic: Boolean logicBoolean logic AND, AND OR, OR XOR XOR NOT. NOT These can be useful both for creating complicated conditional statements and processing boolean logic. conditional statementsboolean logicconditional statementsboolean logic
Simple operations Most ALUs can perform the following operations: Integer arithmetic operations (addition, subtraction, and sometimes multiplication and division, though this is more expensive) Integeraddition subtractionmultiplication division Integeraddition subtractionmultiplication division Bitwise logic operations (AND, NOT, OR, XOR) Bitwise logic operationsANDNOTORXOR Bitwise logic operationsANDNOTORXOR Bit-shifting operations (shifting or rotating a word by a specified number of bits to the left or right, with or without sign extension). Shifts can be interpreted as multiplications by 2 and divisions by 2. Bit-shiftingsign extension Bit-shiftingsign extension
Inputs and outputs The inputs to the ALU are the data to be operated on (called operands) and a code from the control unit indicating which operation to perform. Its output is the result of the computation. operandscontrol unitoperandscontrol unit In many designs the ALU also takes or generates as inputs or outputs a set of condition codes from or to a status register. These codes are used to indicate cases such as carry-in or carry-out, overflow, divide-by-zero, etc. status registercarryoverflowdivide-by-zerostatus registercarryoverflowdivide-by-zero
Control unit 1) The control unit (often called a control system or central controller) manages the computer's various components; 2) it reads and interprets (decodes) the program instructions, 3) transforming them into a series of control signals which activate other parts of the computer. 4) A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from. program counter register program counter register
The control system's function The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU: Read the code for the next instruction from the cell indicated by the program counter. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems. Increment the program counter so it points to the next instruction. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code. Provide the necessary data to an ALU or register. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation. Write the result from the ALU back to a memory location or to a register or perhaps an output device. Jump back to step (1).
Memory hierarchy The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. hierarchicalstoragecomputer architectureshierarchicalstoragecomputer architectures It is designed to take advantage of memory locality in computer programs. memory localitycomputer programs memory localitycomputer programs Each level of the hierarchy has the properties of higher bandwidth, smaller size, and lower latency than lower levels. bandwidthlatencybandwidthlatency
Categorizations of Memory On the basis of physical characteristics a. Volatile/Non-volatile b. Erasable/Non-Erasable On the basis of various technique to design a. Semiconductor b. Magnetic Memory c. Optical Memory On the basis of Access methods a. Random access memory b. Sequential access memory On the basis of location a. Internal – Primary b. External –Secondary
Volatile Memory Information is lost when power is switched off. Non-volatile Memory Information once stored is permanent
All RAM except the CMOS RAM used for the BIOS is volatile Memory that loses its contents when the power is turned off. A computer's main mem., made up of dynamic RAM or static RAM chips, loses its content immediately upon loss of power. Contrast ROM, which is non-volatile memory. Generally abbreviated as NVRAM, Non- volatile memory is an area of data storage in the memory where data is not lost when the power is turned off. Nonvolatile memory areas include read-only memory (ROM) and flash memory
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