Machine instruction

A machine-encoded operation executed by a processor. An assembly language mnemonic can denote one machine instruction or an assembler expansion into several.

An instruction changes architectural state only if a specified predicate holds. With register renaming, a false conditional write must preserve the preceding logical destination value and satisfy younger consumers of that version.

A machine instruction that writes data to computer memory. A store buffer can separate local completion from visibility to other CPU cores.

A machine instruction that reads a value from computer memory into a processor register. A demand cache miss may delay its result; a software prefetch has no such architectural result.

The arrangement of bits specifying an operation, its operands and any immediate constants. A fixed-width encoding has a finite budget shared between these fields.

An operation-selecting field of a machine instruction. A primary opcode can select a family whose individual operations are distinguished by secondary function fields.