Instructions per second

Instructions per second (IPS) is a measure of a computer's processor speed. Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches, whereas realistic workloads typically lead to significantly lower IPS values. The performance of the memory hierarchy also greatly affects processor performance, an issue barely considered in MIPS calculations. Because of these problems, synthetic benchmarks such as SPECint or Dhrystone are now generally used to estimate computer performance in commonly used applications, and raw IPS has fallen into disuse.

The term is commonly used in association with a numeric value such as thousand instructions per second (kIPS), million instructions per second (MIPS), and billion instructions per second (GIPS).

Thousand instructions per second

Before standard benchmarks were available, average speed rating of computers was based on calculations for a mix of instructions with the results given in kilo Instructions Per Second (kIPS). The most famous was the Gibson Mix, produced by Jack Clark Gibson of IBM for scientific applications. Other ratings, such as the ADP mix which does not include floating point operations, were produced for commercial applications. Computer Speeds From Instruction Mixes pre-1960 to 1971 has results for around 175 computers, providing scientific (Gibson) and commercial (ADP) ratings. For IBM, the earliest Gibson Mix calculations shown are the 1954 IBM 650 at 0.06 kIPS and 1956 IBM 705 at 0.5 kIPS. The results are mainly for IBM and others known as the BUNCH — Burroughs, UNIVAC, NCR, CDC, and Honeywell.