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What is a Computer
A computer is an electronic device that manipulates information, or "data." It has the ability to store, retrieve, and process data. You can use a computer to type documents, send email, and browse the internet. You can also use it to handle spreadsheets, accounting, database management, presentations, games, and more
Hardware is any part of your computer that has a physical structure, such as the computer monitor or keyboard.
• Software is any set of instructions that tells the hardware what to do. It is what guides the hardware and tells it how to accomplish each task. Some examples of software are web browsers, games, and word processors such as Microsoft Word
Components
Computers come in all types and sizes. There are primarily two main sizes of computers. They are:
• Portable
• Desktop
The portable computer comes in various sizes and are referred to as laptops, notebooks, and hand-held computers. These generally denote different sizes, the laptop being the largest, and the hand-held is the smallest size. This document will mainly talk about the desktop computer although portable computer issues are also discussed in various areas.
Computer Components:
Computers are made of the following basic components:
1. Case with hardware inside:
1. Power Supply - The power supply comes with the case, but this component is mentioned separately since there are various types of power supplies. The one you should get depends on the requirements of your system. This will be discussed in more detail later
2. Motherboard - This is where the core components of your computer reside which are listed below. Also the support cards for video, sound, networking and more are mounted into this board.

1. Microprocessor - This is the brain of your computer. It performs commands and instructions and controls the operation of the computer.
2. Memory - The RAM in your system is mounted on the motherboard. This is memory that must be powered on to retain its contents.
3. Drive controllers - The drive controllers control the interface of your system to your hard drives. The controllers let your hard drives work by controlling their operation. On most systems, they are included on the motherboard, however you may add additional controllers for faster or other types of drives.

3. Hard disk drive(s) - This is where your files are permanently stored on your computer. Also, normally, your operating system is installed here.
4. CD-ROM drive(s) - This is normally a read only drive where files are permanently stored. There are now read/write CD-ROM drives that use special software to allow users to read from and write to these drives.
5. Floppy drive(s) - A floppy is a small disk storage device that today typically has about 1.4 Megabytes of memory capacity.
6. Other possible file storage devices include DVD devices, Tape backup devices, and some others.
2. Monitor - This device which operates like a TV set lets the user see how the computer is responding to their commands.
3. Keyboard - This is where the user enters text commands into the computer.
4. Mouse - A point and click interface for entering commands which works well in graphical environments
Computer sizes and power
Computers can be generally classified by size and power as follows, though there is considerable overlap:
• Personal computer: A small, single-user computer based on a microprocessor.
• 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.
• Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously.
• Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second
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 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.

Minicomputer
It is a midsize computer. In the past decade, the distinction between large minicomputers and small mainframes has blurred, however, as has the distinction between small minicomputers and workstations. But in general, a minicomputer is a multiprocessing system capable of supporting from up to 200 users simultaneously.

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. Like personal computers, most 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.
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 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.
• Memory and Storage
Memory is also known as primary storage, primary memory, main storage, internal storage, main memory, and RAM (Random Access Memory); all these terms are used interchangeably by people in computer circles. Memory is the part of the computer that holds data and instructions for processing. Although closely associated with the central processing unit, memory is separate from it. Memory stores program instructions or data for only as long as the program they pertain to is in operation. Keeping these items in memory when the program is not running is not feasible for three reasons:
o Most types of memory only store items while the computer is turned on; data is destroyed when the machine is turned off.
o If more than one program is running at once (often the case on large computers and sometimes on small computers), a single program can not lay exclusive claim to memory.
There may not be room in memory to hold the processed data
The following table summarizes the characteristics of the various kinds of data storage in the storage hierarchy.
Storage Speed Capacity Relative Cost ($) Permanent?
Registers Fastest Lowest Highest No
RAM Very Fast Low/Moderate High No
Floppy Disk Very Slow Low Low Yes
Hard Disk Moderate Very High Very Low Yes
The Central Processing Unit (CPU)
The computer does its primary work in a part of the machine we cannot see, a control center that converts data input to information output. This control center, called the central processing unit (CPU), is a highly complex, extensive set of electronic circuitry that executes stored program instructions. All computers, large and small, must have a central processing unit
The Control Unit
The Arithmetic/Logic Unit
Registers:
Memory and Storage
Memory is also known as primary storage, primary memory, main storage, internal storage, main memory, and RAM (Random Access Memory); all these terms are used interchangeably by people in computer circles. Memory is the part of the computer that holds data and instructions for processing
How do data and instructions get from an input device into memory? The control unit sends them. Likewise, when the time is right, the control unit sends these items from memory to the arithmetic/logic unit, where an arithmetic operation or logical operation is performed. After being processed, the information is sent to memory, where it is hold until it is ready to he released to an output unit
ALU
ALU is one of the many components within a computer processor. The ALU performs mathematical, logical, and decision operations in a computer and is the final processing performed by the processor. After the information has been processed by the ALU, it is sent to the computer memory.
A control unit is circuitry that directs operations within the computer s processor by directing the input and output of a computer system. The processor then controls how the rest of the computer operates (giving directions to the other parts and systems). A control unit works by gathering input through a series of commands it receives from instructions in a running programs and then outputs those commands into control signals that the computer and other hardware attached to the computer carry out.