MIPS - chapter ( lesson 2.1 )



MIPS



A processor obeys the instructions which make up a program. How fast the program is carried out depends on how many instructions the processor can obey per second. Following this idea to its logical conclusion you might think that it would be possible to’ give each processor a speed rating in terms of the ‘number of instructions per second’ it can obey, analogous to a ‘miles per hour’ rating for a car. Unfortunately this isn’t possible because not all instructions that the processor is called on to obey take the same amount of time. In other words, how many instructions per second a processor can execute depends on the particular instruction in which you are interested! For example, to make the comparison between two different processors seem favorable in a particular direction all you have to do is count how many simple instructions per second one can execute compared to how many complex instructions the other manages. You might think that this sleight of hand would be easy to detect, but in practice it is not so easy to determine what is a simple and what is a complex instruction when dealing with two completely different processors.



The idea of a measure of the number of instructions per second can be rescued by introducing a standard mix of instructions. that can be used to find out how many instructions on average the processor will obey in a second. This corresponds to the often quoted measure of processor speed - MIPS or Millions of Instructions Per Second. So a machine that is capable of say 2 MIPS will obey 2 million instructions per second on average.



Average MIPS is a useful measure of how fast a processor runs but it can still be misleading. For example, suppose a processor was very good at a particular operation - addition say - and your application used this operation very heavily. The fact that it was exceptionally good at addition would only increase the MIPS rating a little, but it would have a powerful impact on your application! The point is that MIPS is an


EmoticonEmoticon