Computing Revision cards for the exam!

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  • Created by: Haydn May
  • Created on: 19-04-12 14:51

The CPU (Central Proccessing Unit)

The CPU is often known as the brain of the computer. it processes data and is where all the sorting, calculating and decision making is done.The CPU deals with all of the data and processing required to make tasks such as Checking emails or writing an essay possible.

The Fetch Execute Cycle

The Fetch Execute Cycle is the process that makes all this stuff possible. These are the main things that you need to remember.


The CPU fetchs data and instructions from the main memory and then stores it in its internal memory areas (these are temporary). Tese are called registers. The CPU makes use of a vital hardware pass called the "Addess Bus". The CPU Places the addresses of the next item to be fetched on the address bus

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The Fetch Execute Cycle Cont.

Fetch Cont:

Data from this address then moves main memory into the CPU by travelling along another hardware path called the "Data Bus".


The next step is for the CPU to make sense of the instruction it has jsut fetched. This process is called "Decode".

The CPU is designed to understand a specific set of commands. these are called the "Instruction Set" of the CPU. Each make of the CPU has a different "Instruction Set". The CPU Decodes the instruction and prepares various areas within the chip in readiness of the next step

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The Control Unit

TheThree Main parts of a CPU are:

  • Control Unit
  • Immediate Access Store (IAS)
  • Arithmetic And Logic Unit (ALU) 

The control unit has three main jobs:

1. It controls and monitors the hardware attached to the system to make sure that the commands given to it by the application software are used. For example, if you send something to print, the control unit will check that the instructions are sent to the printer.

2. It controls the input and output of data so that the signals go to the right place at the right time.

3. It controls the flow of data within the CPU - which is the "Fetch Execute Cycle". 

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The Immediate Access Store (IAS)

The IAS holds the data and progras needed at that instant by the control unit. The CPU reads data and programs kept on the backing storage and stores them temporarily in the IAS's memory. 

The CPU needs to do this becasue backing storage (the hard disk) is too slow to be able to run applications directly. Data and programs are first loaded into the main memory and then the CPU fetches the part it needs and loads it into the internal registers as part of the "Fetch Execute Cycle".

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The Aritmetic And Logic Unit (ALU)

This is where the computer processes data either by manipulating it or acting upon it. it consists of two main parts:

1. Aritmetic Part

This performs the calculations on the data E.g. 3+2 = 5

2. Logic Part

This deals with logic and comparisions. for example, it works out if one value is greater, less or equal to another.

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Thank you this was really helpful :) Do u do have any notes on Visual Basic Programming ?

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