Million Instructions per Second (MIPS)

MIPS — Million Instructions per Second — is a measure of processor performance expressing the number of machine instructions a CPU can execute per second.

It was a commonly used metric during the 1980s and early 1990s, particularly in contexts where hardware had to meet specific performance budgets. In the embedded and defense sectors, systems running [safety-critical] software — including programs written in [Ada] for the US Department of Defense — were routinely specified and selected on the basis of their MIPS rating.

The metric also featured in debates about compiler efficiency. Early Ada compilers were criticized for generating less optimized machine code than equivalent C or assembly programs, and MIPS was the common yardstick against which this overhead was measured.

As a performance metric, however, MIPS has significant limitations — to the point where it acquired the sardonic backronym "Meaningless Indicator of Processor Speed". Because different processor architectures execute different instruction sets, and because individual instructions vary considerably in complexity and execution time, a raw MIPS figure cannot be meaningfully compared across architectures. Nor does it account for memory access patterns, pipeline stalls, cache behavior, or the actual computational work accomplished per instruction.

For these reasons MIPS has been largely superseded by more representative benchmarks, such as SPEC CPU, which measure real-world workload throughput rather than raw instruction throughput.