Since the modern day GPUs with support for general purpose calculations, it has been pushed that they contain several hundreds of “Cores”, a magnitude higher than the amount of “Cores” you can find in a regular CPU, which these days are about 2-4 depending on your version of CPU. Now, this is due to marketing only, and it has bothered me for a while seeing how academicians and computer engineers have started to pick up the term core, using it relentlessly.

Now, the problem arises due to two major facts. First, a the comparison between what the general CPU manufacturers calls a “Core” (Intel, AMD etc.), and that what GPU manufacturers ( Nvidia, AMD/ATI ) calls a core, is in fact two similar, but different things. Typically, the modern GPU normally consists of several “Cores”, as seen in the following illustration of the new Fermi architecture:

What you can see in this photo is that the GPU core is a scaled down version of what the CPU manufacturers would call ALU, or a functional unit. Now, compare this to the microarchitecture of a Core2 chip, and check out the yellow boxes. If you want to compare the amount of real cores, these are the ones you have to look at. Furthermore, it’s important to remember that the Core2 even have a vector unit, which can multiply / add several operands at once.

Thus, what might be a more fair comparison is the number of multiprocessors in the GPU contra the number of cores on a CPU. In the newest Fermi architecture this is 16, contra the 4 cores on a quad core processor.

However, this is still an unfair comparison. The reason why is due to the type of applications the different architectures are optimized for. Needless to say, the GPU is optimized for graphics processing and stream processing, which in turn is just to churn out data with fairly regular behaviour and memory accesses. Thus, the complexity of of the GPU has been scaled down compared to that of an CPU which has to perform better on a much wider range of applications. Hence, what happens is that the CPU has to use a lot more resources / gates on control structures, leaving the control to calculation gate ratio much higher than found in a GPU. This again, leads to the huge differences between the number of “cores” between the CPU and GPU.

As a sidenote, there are still a lot of applications where the CPU outperforms the GPU

http://www.realworldtech.com/page.cfm?ArticleID=RWT093009110932&p=1

and

http://techreport.com/articles.x/17670

Quite interesting to see how they are turning back to a more G80ish architecture again.