A simpler measure of performance, and one more often quoted than MIPS, is clock speed. Every computer has a master clock which serves to co-ordinate everything that happens. An instruction will always take an exact number of clock pulses to complete and so how fast a program runs is directly dependent on the clock rate. Clock rate is measured in MHZ or Mega-Hertz. (Hertz was a pioneer of radio transmission and the international measure of frequency is named after him.) Roughly speaking 1MHz is one million clock pulses per second and you can use the measure of clock rate to deduce the running time of a program on different machines. For example, if you are running a program on a machine with a clock rate of 1MHz and it takes one minute then changing to a 2MHz machine of the same type will mean that it only takes half a minute to complete.
Well, to be strictly accurate this reasoning only holds if the program’s running speed is only affected by the rate at which the processor obeys instructions and in practice this isn’t the case. For example, if the program in question spends a lot of time waiting for you to type on the keyboard or for a slow
disk drive to deliver up its data then doubling the clock speed ..
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