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Parts of a computer

The hardware of computer is divided into three broad categories:

1. Processor unit

2. Memory3. I/O (input/output).

Processor

The processor is the part of the computer that actually does the computations. This issometimes called an MPU (main processor unit) orCPU (central processing unit or

central processor unit).

A processor typically contains an arithmetic/logic unit (ALU), control unit (CU).

Arithmetic/Logic Unit (ALU)

An arithmetic/logic unit (ALU) performs integer arithmetic and logic operations.

It also performs shift and rotate operations and other specialized operations. Usually

floating point arithmetic is performed by a dedicated floating point unit (FPU), whichmay be implemented as a co-processor.

Control Unit (CU)

Control units are in charge of the computer. Control units fetch and decode machine

instructions. Control units may also control some external devices.

Main Storage

Main storage is also called memory or internal memory (to distinguish from externalmemory, such as hard drives).

RAM is Random Access Memory, and is the basic kind of internal memory. RAM is

called random access because the processor or computer can access any location inmemory (as contrasted with sequential access devices, which must be accessed in order).

RAM has been made from reed relays, transistors, integrated circuits, magnetic core, or

anything that can hold and store binary values (one/zero, plus/minus, open/close,positive/negative, high/low, etc.).

Static RAM is called static because it will continue to hold and store information evenwhen power is removed. Magnetic core and reed relays are examples of static memory.

Dynamic RAM is called dynamic because it loses all data when power is removed.

Transistors and integrated circuits are examples of dynamic memory.

ROM is Read Only Memory (it is also random access, but only for reads). ROM is

typically used to store things that will never change for the life of the computer, such as

low level portions of an operating system

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Input

Input devices are devices that bring information into a computer. Information and

commands are issued to the computer by way of input devices.

Examples of input devices include the keyboard, mouse, modem, joystick, digitizing penand tablet, microphone, touch screens, scanner, camera.

Output Output devices are devices that bring information out of a computer.

Pure output devices include such things as card punches, paper tape punches, LED

displays (light emitting diodes), monitors, printers, and pen plotters.

Data storage device.

Computer data storage, often called storage ormemory, refers to computer

components and recording media that retain digital data used for computing for some

interval of time. Computer data storage provides one of the core functions of the moderncomputer, that of information retention. It is one of the fundamental components of all

modern computers A data storage device is a device for recording (storing) information(data).

Primary storage

Primary storage (ormain memory orinternal memory), often referred to simply as

memory, is the only one directly accessible to the CPU. The CPU continuously reads

instructions stored there and executes them as required. Any data actively operated on is

also stored there in uniform manner.

Secondary storage

A hard disk drive with protective cover removed.

Secondary storage (orexternal memory) differs from primary storage in that it is notdirectly accessible by the CPU. The computer usually uses its input/output channels to

access secondary storage and transfers the desired data using intermediate area in primary

storage. Secondary storage does not lose the data when the device is powered downit is

non-volatile. In modern computers, hard disk drives are usually used as secondarystorage.

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Tertiary storage

Tertiary storage ortertiary memory, provides a third level of storage. Typically it

involves a robotic mechanism which will mount(insert) and dismountremovable mass

storage media into a storage device according to the system's demands; this data is oftencopied to secondary storage before use. It is primarily used for archival of rarely accessed

information since it is much slower than secondary storage (e.g. 560 seconds vs. 1-10

milliseconds). This is primarily useful for extraordinarily large data stores, accessed

without human operators.Off-line storage

Off-line storage is a computer data storage on a medium or a device that is not under the

control of a processing unit.The medium is recorded, usually in a secondary or tertiarystorage device, and then physically removed or disconnected. It must be inserted or

connected by a human operator before a computer can access it again. Unlike tertiary

storage, it cannot be accessed without human interaction