HD constrained.
For the most part I agree that PCs are normally constrained by their HDs. Its not true when you are doing video rendering and gaming and you have enough memory.
I actually use quite an old PC for my normal office work but it does have a good disk system. The main drive(s) is a 120GB RAID mirror using a pair of WD drives on a 3Ware controller - an excellent board and the best $129 I ever spent - no more HD head crashes!
Then I have a "scratch drive" which is a high-speed SCSI Seagate Cheetah resued from a defunct Dell server. That drive hosts the temp files, spooler dir, pagefile, logfiles, event files, temp internet files - in fact anything that is unimportant and would be otherwise written to the RAID system. I really don't want stuff written to my system drive unless really necessary.
I recommend splitting drive storage between system, data & scratch - it improves performance, reduces fragmentation & wear on the drives.
Also do a search on power protected caching and the Microsoft utility dskcache. Make quite a difference if you have a UPS or a laptop.
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