AMD 250 manual Important New Terms, Primitive Operations, Internal Instruction Formats

Software Optimization Guide for AMD64 Processors 25112 Rev. 3.06 September 2005

1.4Important New Terms

This section defines several important terms and concepts used in this guide.

Primitive Operations

AMD Athlon 64 and AMD Opteron processors perform four types of primitive operations:

•Integer (arithmetic or logic)

•Floating-point (arithmetic)

•Load

•Store

Internal Instruction Formats

The AMD64 instruction set is complex; instructions have variable-length encodings and many perform multiple primitive operations. AMD Athlon 64 and AMD Opteron processors do not execute these complex instructions directly, but, instead, decode them internally into simpler fixed-length instructions called macro-ops. Processor schedulers subsequently break down macro-ops into sequences of even simpler instructions called micro-ops, each of which specifies a single primitive operation.

A macro-opis a fixed-length instruction that:

•Expresses, at most, one integer or floating-point operation and one load and/or store operation.

•Is the primary unit of work managed (that is, dispatched and retired) by the processor.

A micro-opis a fixed-length instruction that:

•Expresses one and only one of the primitive operations that the processor can perform (for example, a load).

•Is executed by the processor’s execution units.

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