The Xeon E5 also supports faster DDR3 RAM than the Core i5 and Core i7, and it has much more L3 cache, meaning it needs to resort to using your Mac's main memory less often. In short, the Xeon can run hotter, and therefore faster than desktop or mobile processors, can execute more instructions per second, and can shuttle data back and forth much more quickly.
Does it matter which processor you choose?
Does the processor you choose make much difference? Yes. And no. Every use case is different and so every user's needs are different. The first thing to note is that your choice of processor will be dictated by the Mac you choose to buy. Not every Mac allows you to choose a processor, and those that do have limited options. You can't, for example, put a Xeon E5 in an iMac.
So the question becomes: is your money better spent upgrading the processor when you order a new Mac, or is it better spent adding more RAM or faster storage? Guess what the answer to that one is? Yep, it depends. If you're going to use your new Mac for 3D modelling, video encoding or financial or scientific modelling, the more powerful the processor the better, and so that's where you should spend your money.
If, on the other hand, you work with huge images in Photoshop, work with large spreadsheets or databases, then more RAM is a better investment than a faster processor.
The good news is that every current Mac comes fitted as standard with a processor that's more than capable of handling almost everything most of us are likely to throw at it.
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