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Processor Architecture

1.                   Central Processing Unit – CPU

The main processing unit of the system, also known as the processor. It follows the instructions of the processor.


2.                   Input

Inputs allow interactions with the computer from the CPU. We can input commands and data into the system.


3.                   Output

Outputs allow interactions with the computer from the CPU.


4.                   Arithmetic and Logic Unit – ALU

This is an internal part of the CPU that carries out calculations on data. The arithmetic part uses the usual operators such as multiply, divide, add and subtract. The logic carries out comparisons like ‘equal to’, ‘greater than’, ‘less than’. Values need to be put into the accumulator for calculations to be done.


5.                   Control Unit

This is an internal part of the CPU and it controls the flow of data through the CPU. It also controls the interactions between the different parts of the CPU.


6.                   Memory Unit

The memory unit is the principal storage of the computer. All the data and instructions that the computer needs at a moment are stored here.


7.                   Address Bus

An address bus is a computer bus (a series of lines connecting two or more devices) that is used to specify a physical address. The width of the address bus determines the amount of memory a system can address. For example, a system with a 32-bit address bus can address 232 (4,294,967,296) memory locations.


8.                   Control Bus

A control bus is a computer bus that is used by the CPU to communicate with devices that are contained within the computer. This occurs through physical connections such as cables or printed circuits.


9.                   Data Bus


A data bus is a system within a computer or device, consisting of a connector that provides transportation for data.


Fetch – Decode – Execute cycle


1.                   Fetch

The CPU collects the data and stores it in its own internal memory locations (IAS). To get the instruction the CPU has to use the address bus. The CPU puts the address of the item that it needs to be fetched on to the address bus. This data is then moved from the main memory into the IAS in the CPU by travelling along the data bus. Registers will then decode the instruction.


2.                   Decode

The CPU will understand the instruction it has just fetched. To do this it needs to decode the instruction. The CPU is designed to understand a set of commands, this is known as the ‘instruction set’ and the CPU uses this in order to decode the instruction. The moving of data and the decoding of instructions is controlled by the CPU.


3.                   Execute

The CPU now understands the instruction and can now execute the instruction. This is where any processing of the data that is needed for the instruction can take place. The CPU carries out the instruction. If any arithmetic calculations are needed in the instruction this will be carries out by the ALU.

    Computer Model 1


   Von Neumann Diagram


    Fetch - Decode - Execute cycle


  Inside a computer chip


1.            Little Man Computer – processor simulator


2.            YouTube clip showing how computer chips are made


3.            YouTube clip showing how computer chips work




1.            Processor Terms – worksheet

2.            Little Man Computer – notes and worksheet