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I am a web designer and I'm considering purchasing a Mac Pro (one of the new cylindrical ones). I've scoured the internet for information on the different processor options that they offer, but I'm not really sure what will best suit my needs. I'm looking for some clarification on the advantages and disadvantages of a CPU with a higher clock speed (3.5 MHz) and lower cores (6 core) VS. a CPU with lower clock speeds (2.7 MHz) and more cores (12 core).

Here are the options right off of Apple's site:

When comparing processors with different clock speed, number of cores, and L3 cache size, which one should you choose and why?

slhck
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Digital Brent
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2 Answers2

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The difference between those CPUs is not just in the L3, each step up has more cores, and more L3 to share cache between them.

Basically more cores and especially more L3 cache will mean better multi-threaded performance. Note that this is not the same as but is related to multi-tasking.

Video processing, especially transcoding one format or one resolution to another, is a task that can almost always benefit from more CPU cores. Especially in programs that lack GPU based video decoding and encoding or for systems that have a GPU that has relatively poor performance. A large L3 cache would allow a bigger segment of data to be brought onto the CPU, for the multi-threaded encoder to then work on in parallel. The clock speed might be slightly lower for more cores, but the overall work throughput could be much higher due to having more cores and a larger (faster than main memory) cache to store a good amount of data in.

In order to objectively assess what you are going to buy you need to work out what tasks you are going to use it for and find out if they are capable of being split across multiple cores.

Graphics design/manipulation can also probably benefit from multithreading as it is generally a large amount of memory merging and manipulation through filters, convolves and other effects. A well written application would probably make good use of more cores and the net gain per core is probably a lot higher than the net loss in terms of CPU frequency.

Tasks that can generally benefit from more cores (to my limited knowledge) include:

  • video transcoding (i.e. converting from mpeg-2/DVD to mpeg4 or similar)
  • batch audio processing
  • software compiling
  • 3D CAD (to a certain extent)
  • Graphic design
  • scientific data processing (big data sets, same process to be run across them all)

Tasks that are more memory than CPU bound, therefore cores/cache are less important:

  • browsing the Internet (lots of tabs)
  • social media

Tasks that generally work better with faster cores (but >2 cores definitely helps):

  • Gaming

Heavy mutitasking, such as having a lot of applications loaded, will depend a lot on the type of tasks you want to keep running and whether they are actually doing something. If they are sitting in the background but not actually working then you want more memory, if you want to work on something else while another task is "doing it's thing" in the background, then the CPU will matter more.

Mokubai
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I'm looking for some clarification on the advantages and disadvantages of a CPU with a higher clock speed (3.5 MHz) and lower cores (6 core) VS. a CPU with lower clock speeds (2.7 MHz) and more cores (12 core).

You're asking the wrong questions. Clock speeds are not indications of processor performance unless other factors are the same. Since you're comparing very different CPUs, other factors are not the same, and you can't use clock speeds as a measure of performance.

Essentially, what you're doing is as nonsensical as comparing cars based on how many cylinders they have and how big their gas tanks are. You care about how good a car is, not how it is good.

So ignore the cache sizes, ignore the clock speeds. Instead, look at how quickly the CPU gets work done. You can find this information on benchmarking sites like PassMark.

One quirk you do have to take into account is that with equal benchmarks, more cores is worse. Why? Because the more cores a CPU has, the harder it is to get its full performance because not all workloads can utilize all the cores.

When I'm comparing CPUs, I usually use three numbers:

  1. The price of the CPU.

  2. The benchmark score.

  3. The benchmark score divided by the number of physical cores.

The reason for the first number is obvious. The second number gives me an idea of the raw power of the CPU on complex tasks that can utilize all its cores. The third number gives me an idea of the single task performance of the CPU on code that cannot take advantage of all its cores.

David Schwartz
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