Drilling Down: How the Processor Processes | Year 9 Computing (Cambridge) PDF Download

Understanding Computer Processors

A computer processor, often referred to as the central processing unit (CPU), is the brain of the computer. It carries out instructions from programs by performing basic arithmetic, logic, control, and input/output operations specified by the instructions.

Key Functions of a CPU

• Fetch: The CPU retrieves instructions from the computer’s memory.
• Decode: The CPU translates the instructions into a form it can understand.
• Execute: The CPU performs the instructions.
• Store: The CPU writes the result back to memory.

How Data is Processed

Data processing involves the CPU taking raw data as input and converting it into meaningful information. The process typically follows these steps:

• Input: Data is entered into the computer system via input devices like a keyboard or a mouse.
• Processing: The CPU processes the data according to the instructions provided by the software.
• Output: The processed data is outputted via devices like monitors or printers.
• Storage: The data can be stored for future use in storage devices such as hard drives or SSDs.

Example:

• Typing a letter (input) on a keyboard.
• The CPU processes each keystroke and converts it into a digital signal (processing).
• The letter appears on the screen (output).
• The document is saved to the hard drive (storage).

Instruction Sets and Cycles

An instruction set is a group of commands for a CPU in machine language. The CPU uses these commands to perform operations on data.
Different CPUs may have different instruction sets:

• Basic Operations in an Instruction Set:
  • Arithmetic Operations: Addition, subtraction, multiplication, and division.
  • Logic Operations: AND, OR, NOT, XOR.
  • Data Movement: Moving data between registers or between memory and registers.
• Instruction Cycle: This is the cycle that the CPU goes through to process an instruction. It includes:
  • Fetch Cycle: The CPU fetches the instruction from the memory.
  • Decode Cycle: The CPU decodes the instruction to understand what action is required.
  • Execute Cycle: The CPU executes the instruction.
  • Store Cycle: The CPU stores the result of the execution back into memory or a register.
• Example of an Instruction Cycle:
  • Fetch: CPU fetches the instruction to add two numbers from memory.
  • Decode: CPU determines it needs to add the numbers.
  • Execute: CPU performs the addition.
  • Store: CPU stores the result in a register.

Summary

Understanding how the CPU processes data helps in comprehending how computers function overall. The CPU, through its fetch-decode-execute-store cycle, can process a wide variety of instructions to perform complex tasks. Instruction sets provide the necessary commands that the CPU uses to carry out these tasks efficiently.