Instruction Codes and Instruction Cycle in Computer Organization

What are Instruction Codes?

Instruction codes, often referred to as machine instructions or opcodes, are fundamental to the operation of a computer.
They are a set of binary patterns that specify operations that a computer's central processing unit (CPU) should perform.
These operations can include arithmetic calculations, data movement, control flow, and more.
Understanding instruction codes is key to comprehending how a computer executes programs.
In this example, this binary pattern can represent the sum of two numbers. Each part of the pattern has a special meaning.10110000

Example 1: Simple Instruction Code

Let's consider a simple instruction code in a hypothetical computer architecture:

110110000

In this example, this binary pattern could represent an instruction to add two numbers. Each part of the pattern has a specific meaning.

The first few bits might indicate the operation (addition), and the rest could specify the source and destination of the data.

The instruction cycle is the sequence of steps that a computer follows when executing an instruction.
It involves fetching, decoding, executing, and storing the results of an instruction.
The instruction cycle ensures that the CPU processes instructions one by one, in a systematic manner.

Fetch: The CPU retrieves the instruction from memory.
It does this by using a memory address, which is typically stored in a special register known as the program counter (PC).
Example: If the PC contains the address 1000, the CPU fetches the instruction stored at memory address 1000.

Decode: Once the instruction is fetched, the CPU interprets the instruction code to understand what operation it should perform and what data it should operate on.
Example: If the fetched instruction is the binary pattern 10110000, the CPU decodes it to understand that it's an addition operation.

Execute: With the instruction decoded, the CPU performs the operation specified by the instruction code. This could involve arithmetic, logic, or data manipulation.
Example: For an addition instruction, the CPU would perform the addition operation on the specified data.

Store: After executing the instruction, the CPU may need to store the results back in memory or in registers for later use or for further instructions in the program.
Example: If the addition instruction resulted in a sum, the CPU would store the sum in a specified location in memory.

The CPU repeats this instruction cycle for each instruction in the program, ensuring that the program's tasks are carried out one step at a time.

Instruction codes and the instruction cycle are the basic building blocks of a computer's operation.
Instruction codes, like binary patterns, specify CPU operations. The instruction cycle—fetching, decoding, executing, and storing ensures systematic processing.