But let's get back to the present, and discuss how best to buy a hard drive for your current machine. To begin with, the decision to buy any hard disk should be based on actual needs. Sure, a 400 GB hard disk may appear to be future-proof, but also costs more than two 200 GB drives. This means that the difference in cost may not be justifiable if the drive is going to sit half empty.
This reality is why average users should seek out drives that are no bigger than 250 or 300 GB. The relationship between price and capacity (price per gigabyte) remains acceptable in that size range, and that size offers sufficient storage capacity for the next 12-24 months. The $100 to $150 cost of such drives is also pretty reasonable.
If you're building a new PC or refurbishing an older one, we recommend choosing some variant of Serial ATA for your hard drive interface. These work a little faster thanks to command queuing, are easier to cable up, and cost only a little more than equivalent UltraATA models (sometimes they cost no more at all.) Those whose machines support only UltraATA need not spring for an add-in SATA controller: the slight difference in performance isn't worth the extra cost.
If two versions of the same drive are available, and differ only in the amounts of onboard cache they have, pick the model with the larger one, as long as the price difference isn't too great. As a rule, this means picking a drive with either an 8 or 16 MB cache.
Finally, we'd also like to explore some possible usage scenarios as well. Any drive can act as the system drive for a desktop PC, regardless of the manufacturer. Those for whom the quietest possible operation is of interest should check out drives from Samsung or Seagate. Even though we took no actual sound measurements during our other testing, these drives are well known for their low noise levels.
One more thing: those who put heavy emphasis on a fast system drive and don't want to use a RAID 0 array should be aware that the Western Digital WD740 Raptor remains the best option for that scenario. At $200 or more for 74 GB, this is pretty expensive when compared to other options. That said, the extra cost does provide a noticeable performance boost as well - for example, when starting up Windows or Photoshop - relative to other desktop hard disks.
And now, on to the drives...