Selecting Processors for Your Lion Server Hardware

When Apple’s hardware specs to run OS X Lion Server, you can’t choose any processor the way you can use it with computers. For a specific type of processor, you have to select the Mac model. Within each model there are some differences in clock speed. Mac Pro offers the most choices in processors at the time of purchase, allowing you to choose between one or two multi-core processors.
Multi-core processors act as multiple processors. So two-core processors are equivalent to one quad-core processor. This is why processing power is sometimes described in terms of the number of cores rather than the number of processors.
You don’t need a brand new Mac for Lion Server. An older Mac is just fine — as long as it has a 64-bit Intel processor. Lion will not work on older PowerPC processors.

Sometimes the Mac model name says it all: Your Power Mac has a PowerPC processor. All Mac Pro and MacBook models use Intel processors. However, mini Macs, iMacs, and Xserves come in PowerPC and Intel processor versions.
Only Xserve has an officially upgradeable processor. Apple still has directions on its support site: Find an Xserve processor. You can find PDF documents for every Xserve review, such as the Xserve (early 2008) wizard’s DIY procedure (manual).
You cannot upgrade a PowerPC Mac with an Intel processor. The architecture of the machines is very different. Do not even try.