Million Instructions Per Second
Comparison of processors speeds requires thorough analysis, as the speed of a given CPU is dependent upon many factors, such as the type of instructions being executed, the execution order and the presence of branch instructions (problematic in CPU pipelines). CPU instruction rates are different from clock frequencies, usually reported in Hz, as each instruction may require several clock cycles to complete or may be capable of executing multiple independent instructions at once. Additionally, the number of cycles required for instructions to complete is dependent upon the instruction being executed. MIPS can be useful when comparing performance between processors made from a similar architecture (e.g. Microchip branded microcontrollers). However, MIPS are difficult to compare between CPU architectures. This and other limitations of the unit lead many computer engineers to define MIPS as Meaningless Indicator of Processor Speed.
In the late 1970s, minicomputer performance was compared using VAX MIPS, where computers were measured on a task and their performance rated against the VAX 11/780 that was marketed as a 1 MIPS machine. (The measure was also known as the VAX Unit of Performance or VUP. Though orthographically incorrect, the s in VUPs is sometimes written in upper case.) This was chosen because the 11/780 was roughly equivalent in performance to an IBM System/370 model 158-3, which was commonly accepted in the computing industry as running at 1 MIPS.
Many of the minicomputer performance claims were based on the Fortran version of the Whetstone benchmark. This produces an artificial speed rating in Millions of Whetstone Instructions Per Second (MWIPS). The VAX 11/780 with FPA (1977) is shown as having a rating of 1.02 MWIPS.
Effective MIPS speeds are highly dependent on the programming language used. The Whetstone Report has a table showing MWIPS speeds of PCs via early interpreters and compilers up to modern languages. The first compiler was for BASIC (1982) when a 4.8 MHz 8088/87 CPU obtained 0.01 MWIPS. Results on a 2.4 GHz Core 2 Duo (1 CPU 2007) vary from 9.7 MWIPS using BASIC Interpreter, 59 MWIPS via BASIC Compiler, 347 MWIPS using 1987 Fortran, 1,534 MWIPS through HTML/Java to 2,403 MWIPS using a modern C/C++ compiler.
For the most early 8-bit and 16-bit microprocessors the performance was recognized in thousand instructions per second (kIPS), which equals 0.001 MIPS. The first general purpose microprocessor, the Intel i8080, ran at 0.64 MIPS. The Intel i8086 microprocessor, the first 16-bit microprocessor in the line of processors made by Intel and used in IBM PCs, ran at 0.8 MIPS. Early 32-bit PCs (386) ran at about 3 MIPS.
zMIPS refers to the MIPS measure used internally by IBM to rate its mainframe servers (zSeries, IBM System z9, and IBM System z10).
Weighted million operations per second (WMOPS) is a similar measurement, used for audio codecs.
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