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Which Mac Pro CPU for Photography, Video, Sound?
The August 2010 models offer 4/6/8/12 CPU cores at various clock speeds and widely varying list prices, ranging from $2499 to $5999 or more. There are far more choices than Apple has ever offered before, and this leads to some confusion about which model is best. Since the CPU cannot be upgraded, understanding CPU performance is critical for making an investment in a Mac Pro.
For most all users, the 8-core model at 2.4GHz will almost always be slower than the 6-core model at 3.33GHz. Even the 2.93GHz 12-core model might be slower than the 6-core 3.33GHz model. It all depends on your software and workflow. Paying more for lower performance won't feel good, so which model should you choose, now that Apple offers models with single or dual CPU, and 4/6/8/12 CPU cores?
The "rev limit" — clock speed
The clock speed is the fastest rate at which computer instructions execute— that's assuming enough memory, and that the disk is not involved, either of which idles the CPU. For most software, the clock speed is the primary determinant of "performance".
A 3.33GHz model runs 13.6% faster than 2.93GHz, and 38.7% faster than 2.4GHz. A 13.6% clock speed difference means about 68 seconds vs 60 seconds, or 1.13 seconds vs 1 second — noticeable, but not decisive. But 3.33GHz vs 2.4GHz is substantial eg 83 seconds vs 60 seconds, or about 1.4 seconds vs 1 second — now that you'll notice.
Baking cakes — CPU cores
A dozen chefs cannot bake one cake faster than one chef. But a dozen chefs could bake a dozen cakes in the same amount of time that one chef could bake one cake. That analogy is key to understanding why more CPU cores are not necessarily better: not all tasks are divisible.
We've seen that clock speed is a "rev limit". But the Mac Pro CPU contains one or two CPU chips, and each of those contains four or six CPU cores. These cores can work together in parallel to speed up certain computing jobs. They cannot "bake a cake" faster, but if the software is well written, and the job is to "bake 12 cakes", then a 12-core Mac Pro can get that job done in 1/3 the time that a 4-core Mac Pro could (at the same clock speed).
Alas, it is the software application that determines how many CPU cores actually get used. The application must be written to take advantage of those CPU cores, and few programs are written well enough to take advantage of more than 2-3 cores, with many falling short of even that.
Efficient use means that 12 CPU cores will finish the job in half the time that 6 cores will. This is rare, and using more cores almost always has management overhead. So in reality, a 12-core Mac Pro often has software overhead that often makes it only 50% faster than a 6-core Mac Pro, even if all the cores are in full use.
Many programs are still "single threaded" for some tasks, which means they can use only a single CPU core to get the job done, leaving the remaining cores completely idle. For example, saving a file in Adobe Photoshop™ CS5: only one CPU core is used, so it can take minutes to save a large file (but see this tip).
Taking the cake analogy further, if the job is to "bake 4 cakes", a 4-core Mac Pro at 2.8GHz will get that job done faster than a 12-core Mac Pro at 2.4Ghz; there are enough CPU cores with either model, but a 2.8GHz model is running each core 16% faster, so it will finish sooner.
Very few users can benefit from more than six cores, and the large majority of users are well served by a quad-core Mac Pro. Users with multiple programs running (and doing real work all at the same time) should determine how many CPU cores are being used, then choose a 4/6/8/12 core Mac Pro accordingly.
For peak interactive performance (eg working with brushes, drawing, etc), as well as a "sweet spot" in terms of CPU cores, the 6-core 3.33GHz is the smart move— the combination of fast clock speed and 6 cores addresses 98% of the computing challenges out there.
Mac Pro for photographers
For Adobe Photoshop and Lightroom, RAW converters, etc, a quad-core CPU cores is plenty for most tasks, and most of the time, most of those cores will be idle. However, certain operations in Adobe Lightroom, or RAW converters like PhaseOne CaptureOne Pro can use more than 4 cores effectively.
The 6-core 3.33GHz model is a "sweet spot" which will satisfy most programs, and generally outperform even the 12-core model, because the 6-core model runs at a faster clock speed, and more than six cores are rarely used. Certain specialty software can make use of eight or 12 cores, but such tasks are rare for most users.
Mac Pro for video and sound
Video and sound processing can be very compute-intensive, but it is highly dependent on which software applications are being used. Slow operation does not necessarily mean that more CPU cores will help. Also, a fast video card can contribute to performance. A good choice for many users will be a 6-core 3.33Ghz Mac Pro with the fastest video card. For really large jobs (eg 1080p video), the 2.93Ghz 12-core model will be the right investment. But even a 4-core Mac Pro will deliver a very high level of performance.
With too little memory, the CPU will be stalled— your Mac runs slowly. The best choice for most Mac Pro users is 12GB of memory. Users with big jobs can go to 24/32/48/64GB for big jobs.
Fast drives, including RAID-0 striping, can be important for working with large files. In some cases, use of a quality solid state drive (SSD) can make a world of difference also. But very few users need specialty drives; very high performance can be achieved at reasonable cost with standard SATA hard drives.