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5400 RPM vs. 7200 RPM
Recently I have been seeing posts on newsgroups stating that a newer ATA/100 5400 RPM hard disk (HD) is almost as fast as a 7200 RPM ATA/100, and faster than an older 7200 RPM ATA/66. I have also heard a sales person or two claim the same thing. This just doesn’t seem right to me, since rotational speed is a big factor in not only finding the data on a disk, but also getting it off the disk. So as usual I decided to see for myself. I used three Western Digital HDDs – a 200BB ATA/100 7200 RPM, a 100EB ATA/100 5400 RPM and a 102BA ATA/66 7200 RPM.
It has been said that a picture is worth a thousand words, so let’s let the “pictures” (actually HD Tach graphs in this case) speak first:
WD102BA ATA/66 7200 RPM
WD 100EB ATA/100 5400 RPM
WD 200BB ATA/100 7200 RPM
Well, by looking at the graphs I would say that the claim is correct. But test results in the ATA/100 article I wrote earlier this year showed no real difference in speed in an ATA/100 drive when set to ATA/66 or 100 mode. So why is there a difference between the ATA/66 and 100 drives shown here? There have been some design changes made in the newer ATA/100 drives that enhanced performance – both the 5400 and 7200 RPM units. If it was due to just the ATA/100 mode’s higher burst speed (which doesn’t even show up in the graphs), then I should have seen a similar difference when testing with an ATA/100 drive when set to the slower modes, yet I did not. A couple of other options also come to mind: My initial tests were flawed, but I don’t think so. ATA/100 allows the 5400 RPM drive to sustain a higher initial transfer rate, but I don’t think that is the case here, since the disk buffer is only 2MB, and the drop off starts at well over 4MB (ATA/100 means it can transfer data from the buffer to the controller at that speed). You can rule out that the Windows install is different between the drives, since I used Drive Copy to load the same exact copy of Windows and all the test data on each drive. Or could it be the graphs don’t really give us an accurate picture of what is going on? More to follow…
Before we go any further there are several interesting things on the above graphs. The first being the nice flat line for the ATA/100 7200 RPM drive. The second is the ATA/100 5400 RPM starts off flat, but then starts dropping off from about the middle of the test. Third is that the ATA/66 7200 RPM drive has a curve from the beginning to the end. Fourth is that the ATA/100 5400 RPM and the ATA/66 7200 RPM start off and end at about the same data rates, but the ATA/100 5400 PRM seems to be able to sustain a higher transfer rate for a longer time.
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