Bits of Bytes.co

IGCSE / GCSE Computer Science

  • Home
  • 1 - Theory of Computer Science
  • 2 - Practical Problem Solving and Programming
  • Pre-Release Material
    • 2018 June >
      • 22 >
        • 22 - Cow Task
        • 22 - Task 1
        • 22 - Task 2
        • 22 - Task 3
  • 1 - Computer Systems (2023)
Picture
MENU
  • Home
  • 1 - Theory of Computer Science
  • 2 - Practical Problem Solving and Programming
  • Pre-Release Material
    • 2018 June >
      • 22 >
        • 22 - Cow Task
        • 22 - Task 1
        • 22 - Task 2
        • 22 - Task 3
  • 1 - Computer Systems (2023)
1 - Computer Systems (2023)  / Instruction Sets

CPU - Instruction Sets

Picture


Instruction Sets

In a CPU, the instruction set refers to the different types of operations that a CPU is capable of performing.

When we talk about instruction sets we are referring to the low level machine code instructions that a CPU is built to handle.
Low level operations are split into an opcode and an operand.

Opcode - Represents the machine instruction i.e. what it has to do - ADD, LOAD, STORE or SUBTRACT

​Operand - This is either the value to be operated on OR the address that holds the value to be operated on.

Each CPU only has a limited number of opcodes available to them and the available opcodes is what is referred to as the instruction set.
​
Interesting Point
The available operations are hard coded into each CPU and the consist of electronic circuitry and transistors.  Different instructions will allow the CPU to enable / switch on relevant transistors to perform the required tasks.


Instructions

ach CPU has a limited number of instructions that it is capable of performing.  As the instructions are hard coded with transistors it is obviously not possible to add more with a software update.  Some example instructions include:
​
Operation
Purpose
ADD
Add two numbers
IN
Allow input from a device
SUB
Subtract one number from another
DIV
Divide one number by another
STORE
Store a value in a given location
MUL
Multiply 2 numbers
HALT
Stop operation

Est. 2015 - Copyright © 2020