sonyman wrote:The access time of a 7200 rpm HDD is roughly half of that of a 5400 rpm.
Have to but in here. But your statement is incorrect. Seek times on 5400RPM drives are, on average, the same as 7200 drives...same goes for older 4400 RPM drives.
Access times are reduced because the rotational delay is lower.. on a 7200rpm disk the rotational delay is ~4.2 ms, on a 5400RPM it's ~5ms.
with seek times being roughly 9ms, the access time difference between 7200RPM and 5400RPM drives is ~6%.(which doesn't equate to a direct 6% performance boost in desktop use) 13.2ms is obviously not half of 14ms.
What probably matters more is getting a high platter density. Getting 20Gb platters vs getting 60GB platters(such as the WD 2000JB, 1200BB/JB, 60 and 120GB Seagate ATA V's, and IBM 180GXP) is going to make roughly a 62% increase in performance in a typical desktop senerio. This is because the higher density of the 60gb/platter drives offer nearly 3 times the transfer rates of a 20GB/platter drive.
It should also be noted that the real reason for getting a 7200RPM drive in desktop use is because of the higher transfer rates you can achieve with the same density disks... going to 7200RPM will give you an ~33% increase in transfer rates. This is aproximately the same performance boost you get by going from 20GB to 33GB platters.
20GB/platter drives are definately on the way out, but there are still some around... most IDE drives you will see are using 33, 40, or 60Gb platters. Knowing which ones are which will give you a good performance boost(probably about as much as going to a drive that uses an 8bm cache as opposed to a 2mb one)
My advice to you is to get the drive with the largest buffer and platter density in your price range that meets your capacity requirements. For most people in this forum I would guess this would be the Western digital 800JB, 1000JB, 1200JB and IBM 180GXP in 60/120GB.