Machine instructions

Summary

Machine instructions are patterns of bits that a particular processor can understand. An instruction usually says what action to take and which data or location to use. Assembly language gives people readable names for those actions; it is not the bits themselves.

Introduction

Code such as JavaScript is designed to be convenient for people to write. A CPU cannot directly run that source code. Before the CPU executes the work, compiler or runtime tools translate it into instructions for that processor design.

Explanation

An opcode is the part that selects an action, such as add or load. Operands are the pieces the action uses: values, registers, or memory locations. The exact bit pattern depends on the processor’s instruction set—the list of operations that processor understands. A pattern that works on one kind of CPU may mean nothing on another.

Real-world example

Separate the action from the data

Registers are tiny, very fast storage locations inside a CPU. An instruction can name registers, a location in memory, or a number written directly in the instruction. The processor can perform only the operations in its instruction set.

Code example

LOAD R1, [price]
ADD  R1, R1, R2
STORE [total], R1

ADD is the opcode; R1 and R2 are operands in this simplified example.

Common mistakes

• Assuming all computers share one universal machine language.
• Calling assembly text the actual bits stored in memory.
• Expecting one instruction to implement a complete feature such as “send email”.

Quiz

Key takeaways

• CPUs execute encoded, architecture-specific instructions.
• Instructions combine an operation with operands.
• Assembly is readable notation for low-level operations, not a replacement for the encoded bytes.