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Computer Science Careers

Outside computing

Average pay

Main Jobs

Computer Architecture

Employers

Subject links

Key Skills

80.5% of all jobs require the use of computers. System Architecture can link to most computing and non-computing careers.

£25,000 - £95,000

  1. Computer Hardware Engineer
  2. Computer Systems Analyst
  3. Operating system Engineer
  4. Database administrator

1.Apple

2.Sony

3.Dell

4.Canon

1.Engineering

2.Electronics

3.Network hardware

Can troubleshoot computer issues, manage memory and understand how computers work at a deeper level.

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System Architecture:

Fetch Decode Execute

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Topic Name

Learning Objective:

Text

Learning outcome:

Text

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iCan()

iCan.Explore()

I show an understanding of the topic by briefly describing my understanding

iCan.Enhance()

I show a good technical understanding and am able to show this through detailed description and evaluation of effectiveness.

iCan.Excel()

I can show an excellent technical understanding of the topic and can give factually correct examples and evidence.

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Fetch decode execute

If you have 20 programs open, you may think your computer is running them all at the same time. Infact your computer is running a single instruction at a time (in a standard processor).

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Computers however are very faster and can run over 4 billion instructions a second. Given the illusion of running all the programs at the same time.

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Fetch, decode, execute cycle (basic)

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Each instruction follows the ‘fetch-execute’ cycle.

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The computer fetches the instruction from its memory and then executes it.

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Fetch

Decode

Execute

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Fetch, decode, execute cycle (basic)

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The first step the fetch-execute cycle carries out is fetching the instruction.

The CPU fetches an instruction from the main memory and stores it in the CPU temporary memory.

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Fetch

Decode

Execute

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Fetch, decode, execute cycle (basic)

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Once the instruction has been fetched, the CPU will need to understand the instruction to action it.

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This is called decoding.

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Fetch

Decode

Execute

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Fetch, decode, execute cycle (basic)

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When the instruction has been decoded, the CPU can carry out the action that is needed. This is called executing the instruction.

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The CPU is designed to understand a set of instructions

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Fetch

Decode

Execute

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Fetch (Detailed)

The program counter has the value of the next address to be fetched.

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Fetch (Detailed)

The address is used by the memory address register in order to fetch the instruction from main memory.

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Fetch (Detailed)

The instruction is stored in the memory data register.

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The program counter increases by 1.

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Decode (Detailed)

The instruction is sent to the control unit which then decodes the instruction to see what has to be done.

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Execute (Detailed)

The instruction is then executed. Instruction are executed differently depending on what the instruction is.

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Execute (Detailed)

Load: fetch a certain instruction

Store: Store an instruction back in RAM.

Add: Add data using the accumulator

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Recap

  1. Program counter stores next address
  2. Address sent to the memory address register
  3. Using the address from memory address register, the instruction is fetch from memory and stored in the Memory data register.
  4. The Program counter increases by 1.
  5. The control unit decodes the instruction
  6. The instruction is executed

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And this cycle happens 4 billions times a second in your PC.

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