Is there any difference in execution times between two different processors with same amount of gigaflops?

Question

I have a hardware related question that I debated with a friend.

Consider two processors from two different manufacturers with the same amount of gigaflops put into the same computers (i.e. RAM and such as are the same for both computers).

Now given a simple program will there be any difference in execution times between the two computers with the same processors. I.e. will the two computers handle the code differently (for-loops, while-loops, if-statements and such)?

And if, is that difference noticably or can one say that the computers would approximately perform the same?

Answer 1

Short answer: Yes, they will be different, possibly very much so.

Flops are just about floating point operations, so it is a very very crude measure of CPU performance. It is, in general, a decent proxy for performance for scientific computations of certain kinds, but not for general performance.

There are CPUs which are strong in FLOPS - the Alpha is a historical example - but which have more moderate performance in integer computations. This means that an alpha and an x86 CPU with similar FLOPS would have very different MIPS-performance.

The truth is that it is very hard to make a good generic benchmark, though many have tried.

Answer 2

Another critical factor in comparing the performance of two processors with the same FLOP measure is the rate at which they can move data between CPU and RAM. Add memory cache into your thinking to complicate matters further.