Processor: The Processor Instruction Set

Processor Instruction Set

A Processor Instruction Set refers to the set of instructions that a particular CPU or computer architecture can execute.
It is a fundamental concept in Computer Science, as it dictates what operations or tasks a processor can perform.

Types of Instructions

Arithmetic and Logical instructions: These involve mathematical or logical operations like addition, subtraction, AND, OR, NOT operations.
Data Transfer instructions: These instructions control the movement of data from one part of the computer to another. This includes operations like MOVE, LOAD, and STORE.
Control Flow instructions: These define the sequence in which the instructions are executed, such as JUMP, CALL, RETURN, etc.
Special Purpose instructions: These include unique operations specific to a particular CPU architecture, like interrupt handling or power management instructions.

Role of Instructions

An instruction set does not just contain the type of the instructions but also the format of the instructions. The format includes the different fields an instruction can have and the information each field holds.
Instructions are carried out during the Fetch Decode Execute (FDE) cycle. The Control Unit fetches the instructions from memory, decodes them, and then sends them for execution.
The speed and efficiency of executing these instructions heavily influence the performance of a processor.

Opcode and Operands

Instructions typically consist of the opcode and operand.
The opcode stands for ‘operation code’. It is a portion of a machine language instruction that specifies the operation to be performed.
The operand part of instruction specifies the data or memory locations on which operation needs to be performed.

Complex and Reduced Instruction Set Computing

Complex Instruction Set Computing (CISC) architectures provide a large set of complex instructions. The instructions are of variable size and could take several clock cycles to execute.
Reduced Instruction Set Computing (RISC) architectures, on the other hand, have a smaller set of simpler instructions. The instructions are uniform and are designed to execute in a single clock cycle.
A processor’s instruction set can be either based on CISC or RISC as each has its own set of advantages and drawbacks.

Knowing the processes and details of a processor’s instruction set can help in the understanding of how software and hardware interact, and in the optimisation of both for better performance.