KS3 Computing/Hardware

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At the heart of every computer is the CPU (Central Processing Unit) - the 'brain' of the computer. It refers to that part of the processor which 'processes' the data and instructions.

The Central Processing Unit (CPU), also called a processor, is located inside the computer case on the motherboard.

How the CPU interacts with the memory and other parts

Below is a picture of a standard computer architecture. You can find out more about the components below;

Processor's Main Function

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The main function of a processor is to execute operations, it does this by:

  • Fetching The Next Instruction
  • Decoding The Instruction
  • Executing The Decoded instruction

Until there are no more instructions.

The Components Of A Processor

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The Processor is made up of two components:[1]

  • The Control Unit
  • The Arithmetic Logic Unit

The Control Unit (or CU)
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The control unit decodes each instruction into electrical signals that carry out that instruction and fetch the next instruction.

The Arithmetic Logic Unit (or ALU)
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Carries out all the mathematical and logical operations i.e. addition, subtraction and comparisons (relational operations such as =, < and >)

Could Be Refereed To As The Processing Part Of The Processor.

Memory Unit/ Cache

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A few CPUs always read each instruction from main memory and store the results of each ALU calculation in main memory.

Most CPU chips also include some Very fast memory which is used as an intermediary between the processor and the main memory.

Stores the most frequently or most recently used instructions and data so that they might be retrieved quickly.

Small amount of memory usually.


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A core is a single processor which can fetch and decode instructions. On a multiple core processor there are several processors each simultaneously fetching and executing instructions. Each processor is not faster but the overall rate of fetching and executing instructions is multiplied by the number of cores.

A processor with two cores is called a dual-core processor; a processor with three cores is called a triple-core processor; a processor with four cores is called a quad-core processor; and a processor with six cores is called a hex-core processor. For other numbers of core, the number itself is used, for example a ‘12-core processor’.

The higher the number of cores, the better the performance of the computer

Clock Speed

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The clock speed determines the rate at which instructions are carried out. The higher the clock speed, the faster each instruction is fetched and executed. The processor has an internal clock (which is simply a vibrating crystal). Each time the crystal vibrates is one tick of the clock. The ticks of the clock are then used to synchronise all the parts of the processor. Every operation of the processor takes a fixed number of ticks. Therefore, if the clock is ticking faster, the more instructions are processed.

A processor's speed is measured in megahertz (MHz), or millions of instructions per second, and gigahertz (GHz), or billions of instructions per second. A faster processor can execute instructions more quickly. However, the actual speed of the computer depends on the speed of many different components - not just the processor.

Teaching resources and activities

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CPU Video - https://www.youtube.com/watch?v=P4QmPFcBELE

Purpose of a CPU Video - https://www.youtube.com/watch?v=DvgJZvVyJfA#action=share

Fetch, Execute Cycle Video - https://www.youtube.com/watch?v=drUBm_luhso#action=share

Clock Speed Video - https://www.youtube.com/watch?v=UHIhoLHGTR4#action=share

Processor Fill in the blanks worksheet

Processor Questions Worksheet

Compare processors Get students to look at PC adverts on the internet to get a feel for current specifications or see who can find the fastest processor. http://ark.intel.com/products/family/41877/Intel-Pentium-Desktop-Processor

Extension Activities

Moore's Law - Beyond the boundaries of Computing - http://www.bbc.co.uk/news/technology-32335003

This is a very brief overview of the hardware. See the Wikibook How To Assemble A Desktop PC for more details.

  1. Hossein Bidgoli. "MIS 5". p. 25.