1. GCSE Information Technology Computer Systems 2 Hardware is the name that is given to any part of a computer that you can actually touch. An individual piece of hardware is called a device. The basic hardware of any computer consists of a central processing unit (CPU) along with input, output and backing storage devices.

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3. The central processing unit (CPU) This is the part of the computer where the searching and sorting of data, calculating and decision-making goes on. The CPU contains the Main Memory, the Control Unit and the Arithmetic and Logic Unit (ALU).

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5. The Control Unit fetches instructions from the main memory, decodes them and causes them to be executed by the ALU. The ALU performs calculations and makes decisions using these instructions. The Main Memory contains two types of memory chip called ROM and RAM which hold program instructions and data.

6. GCSE Information Technology Random Access Memory (RAM) RAM is the computer’s ‘working memory’. RAM temporarily stores programs and data that are being used at a given time. The contents of RAM can be changed and are lost when the computer is turned off. Memory which is wiped clean when the computer is turned off is called volatile memory.

7. GCSE Information Technology Read Only Memory (ROM) The main use of ROM memory chips in a computer is to store the program that runs when the computer is turned on which loads the operating system (e.g. Windows 2000) from disk. The contents of ROM can’t be changed and aren’t lost when the computer is switched off. Memory which isn't wiped clean when the computer is turned off is called non-volatile memory.

8. GCSE Information Technology PROM and EPROM PROM and EPROM are both special types of programmable read only memory. PROM stands for Programmable Read Only Memory. This type of memory can be programmed once but can’t be changed again afterwards. EPROM stands for Erasable Programmable Read Only Memory. This type of memory can be programmed and then changed whenever necessary.

9. GCSE Information Technology BITS and BYTES Computers store and process data using binary numbers. A single unit in binary is called a bit which stands for binary digit. Computer memory is measured in bytes. One byte is made up of eight bits. One byte can store one character. The eight bit binary code in this byte represents the letter A

10. GCSE Information Technology The size of a computer’s memory is normally measured in kilobytes (Kb), megabytes (Mb) or gigabytes (Gb). The table below shows some of the main units of size that we use to measure computer memory.

11. GCSE Information Technology Mainframe computers Mainframe computers cost millions of pounds to buy and install. They can process massive amounts of data extremely quickly, which is stored on hundreds of disk drives. A mainframe can have hundreds of terminals and users connected to it at the same time. The most powerful mainframes are called supercomputers.

12. GCSE Information Technology Microcomputers Microcomputers are sometimes called PCs, or personal computers. A typical PC system consists of: A base, or tower, unit that contains a CPU and backing storage devices, normally a floppy disk drive, a hard disk drive and CD-ROM drive, and often a Zip drive; Input devices, normally a mouse and keyboard. Output devices, typically a screen, printer and speakers.

13. GCSE Information Technology Microcomputers Minicomputers cost tens of thousands of pounds to buy and install. They are much more powerful than microcomputers but not as powerful as a mainframes. Medium-sized businesses use minicomputers to control the company network and act as a central store for all the company’s data.