Computing - Computer Systems

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The Components of a Processor

A processor consists of a Control Unit, an Arithmetic Logic Unit and Registers.
Main Memory consists of RAM and ROM.

CPU (Central Processing Unit)

The CPU is made up of a processor and main memory.
The processor fetches and executes the program instructions from main memory.
Main memory stores the program instructions and associated data that is currently being processed.
The processor has three components: the control unit, the ALU and registers.

Control Unit - The control unit sends out signals to manage the fetching and execution of instructions.

ALU (Arithmetic Logic Unit) - The ALU carries out arithmetic and performs logical decisions such as AND, OR, NOT, etc.

Registers - Registers are individual storage locations on the processor chip. They hold items of data that are required to perform its function.
For example, a register called the accumulator temporarily stores the results of calculations performed in the ALU.
Main memory is made up of RAM and ROM.

RAM (Random Access Memory) - RAM can be written to and it is this part of main memory. When they are run, programs are loaded from backing store into this. Any data associated with the program is also loaded into RAM.
RAM is volatile. This means that it loses its contents when the user switches off the computer.

ROM (Read Only Memory) - The programs stored in a ROM chip are put there at manufacture, after which the contents of ROM never change. ROM is used to store part of the computer's operating system, called the BIOS, which is executed when the computer is switched on.
Unlike RAM, if the computer is switched off, then ROM retains its contents. 

Backing Store - Programs and data files are stored permanently on backing store.

Types of Computer

Mainframe - A mainframe is a large powerful computer used by organisations that need to store and process large amount of data. A mainframe computer can cost millions of pounds.

Desktop - A desktop computer is a computer that is too heavy to be easily carried around and is designed to be used at a desk. It will usually have a QWERTY keyboard and a mouse. A QWERTY keyboard gets its name from the first line of letters on the keyboard.

Laptop - A laptop computer is a computer that is portable (easily carried around). It will have a QWERTY keyboard and a touchpad as input devices since. The display is usually a flat TFT (Thin Film Transistor) screen.

Palmtop/PDA - A palmtop or PDA (Personal Digital Assistant) computer is a small portable computer that can easily be held in the hand. It will usually have a special pen, called a stylus, to write on a touch sensitive screen.

Health Risks

Damaged Eyesight - Spending long periods of time staring at a computer screen can have a bad affect on eyesight. One remedy to this problem is to use a screen filter.

RSI (Repetitive Strain Injury) - Some people spend hours



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