When it comes to the actual server hardware, a lot of importance (rightfully) is given to the CPU(s) that drive the server.

Both of the big chipmakers, Intel and AMD, provide server-specific CPUs meant to perform better in server operations. Both of the companies' server-CPUs are very close to their desktop counterparts

Intel offers the Xeon CPU for servers, and have certified them for single-processor and multiprocessor designs. The Pentium 4 on the other hand has been certified for single and dual CPU systems. The Xeon CPUs all have a minimum of 512 kb, whereas some of the Pentium 4 CPUs only feature 265kb.

Similar to what Intel has done, AMD offers the 'Opteron' brand for servers. Similar to its desktop counterpart, the Athlon64, the Opteron is different such that it is designed for multi-CPU situations and can also access greater amounts of RAM than its little brother. Again like the Xeon vs P4 comparison, the Opteron comes with a 1mb cache, whereas the Athlon64 can vary with 1mb, 512kb, or 256kb.

When it comes down to it, it is likely better to get the CPUs (Xeon and Opteron) that are built specifically for servers. While very much like their desktop counterparts, they do have some hardware features meant to be taken advantage of in a server situation.

One most also very acutely aware of what the actual bottleneck is on a server. In almost all cases it is one of the following - CPU, memory, or disk I/O. We have a page explaining server bottlenecks.