Answer:
When computers only had one microprocesser then the question was easy to answer - the frequency at which the on board clock worked how fast if it worked. More recently there have been a series of large computation tests you can run on the computer whcih is supposed to 'tell you the real speed' of you computer. In practice a computer which counts the number of words in a 50 document in 5 seconds is faster than a computer that does the same count in 1 minute