Most vendors define quad-core to mean that you have 4 cores on one CPU even if you have more than one CPU in the computer. Some computer vendors, on the other hand use quad-core to mean the total number of cores in the computer. By this definition a dual processor (2 CPUs) each with two cores would be called a quad-core. The first definition is more meaningful and less mis-leading.

In our cluster at NIST, we have 7 computers with two dual-core processors and 1 computer with two quad-core processors, along with a bunch of other computers with only 1 core per CPU.

There is a benchmark case in the Repository that compares single, duo and quad core computers that may be of interest. The benchmark runs multiple serial FDS4 and FDS5 jobs simultaneously (from 1 to 8). An effective clock rate in GHz (normalized to a 3.8 GHz computer we have) is computed using wall clock times FDS reports. The results are then reported in GHz vs. number of simultaneous jobs run. As expected (at least after the fact!) the duo-core plot dies off quicker than the quad-core plot. Also, two jobs run much better on a dual duo-core than just a dual single core computer. It is interesting to see how they compare to the other and older computers we have.

We did all this because the "definition" of GHz changed between generations of Intel chips and we didn't know how a 3.0 GHz computer from the new generation would compare with a 3.8 GHz computer from the old generation. We were pleased that they behaved very well.