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Concept
Instructions per second
Summary
Instructions per second (IPS) is a measure of a computer's processor speed. For complex instruction set computers (CISCs), different instructions take different amounts of time, so the value measured depends on the instruction mix; even for comparing processors in the same family the IPS measurement can be problematic. Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches and no cache contention, whereas realistic workloads typically lead to significantly lower IPS values. Memory hierarchy also greatly affects processor performance, an issue barely considered in IPS calculations. Because of these problems, synthetic benchmarks such as 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 metric prefix (k, M, G, T, P, or E) to form kilo instructions per second (kIPS), million instructions per second (MIPS), and billion instructions per second (GIPS) and so on. Formerly TIPS was used occasionally for "thousand ips".
IPS can be calculated using this equation:
However, the instructions/cycle measurement depends on the instruction sequence, the data and external factors.
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 in 1959.
Other ratings, such as the ADP mix which does not include floating point operations, were produced for commercial applications. The thousand instructions per second (kIPS) unit is rarely used today, as most current microprocessors can execute at least a million instructions per second.
Gibson divided computer instructions into 12 classes, based on the IBM 704 architecture, adding a 13th class to account for indexing time.
Official source
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