1. Anybody who makes a blanket statement that all 5400 RPM drives are slower than 7200rpm drives doesn't know what they're talking about. It has been proven that higher capacity 5400 RPM drives can be faster than lower capacity 7200 RPM drives because they have a higher aerial density on the platter meaning the drive head and platter do not have to move/spin as far to access non contiguous data.
Backwards. Higher areal density (not aerial---that means something very different) means that it doesn't have to seek as far when doing continuous reads---that a single track contains more data, and thus when doing nearly continuous reads, you're likely to have a greater amount of the data in the track cache buffer without having to do a short seek (and possibly settle) to the next track.
In certain workloads like audio, this does mean that a 5400 RPM drive can be faster than a 7200 RPM drive from a few years earlier. Bear in mind, though, that areal density is affected more by the progress of time than it is by drive speed. As such, a 7200 RPM drive will almost always be faster than a 5400 RPM drive built on the same day by the same manufacturer, and a newer drive at any given speed will pretty much always be faster than an older drive at the same speed because of increases in areal density.
Also, bear in mind that that the boost from areal density is highly workload-dependent. The 5400 RPM drive will still be a lot slower at anything that requires random access (booting, launching applications, etc.) and will be much more susceptible to performance degradation due to fragmentation.
With respect to the issue of seek times and areal density, yes, horizontal seek times do get slightly better as areal density improves, but that is largely drowned out on a single-track "short seek" by the rotational latency to get around to where the block you're looking for is located. On the average, you have to wait half a rotation, or 5.56 milliseconds for a 5400 RPM drive versus 4.17 for the 7200 RPM drive. The difference in that average is actually more than the total seek time track-to-track for many modern drives.
In other words, for audio workloads, that improvement is basically a no-op. For random seek workloads where you're talking about a full seek/settle cycle, that might be different. If you could get an 8 ms seek down to 4 (plus 2 ms settle) by quadrupling the areal density (doubling the TPI), yeah, you'd overcome the extra rotational latency in the most degenerate cases, but that doesn't typically reflect real-world workloads, nor are you likely to see the TPI double quickly. TPI has only roughly tripled between Seagate's 10 GB drives and their current 250 GB drives. That should give you at least some idea of the time frame we're talking about to see a big win in random access workloads due to areal density improvements.
Wow. Getting long-winded here. Sorry, didn't mean to write a dissertation. Oh well. Hope that clears things up anyway.... Just thought I should bring in the perspective of somebody with a bit of storage systems background to clear up any confusion before somebody made a wrong assumption based on your statement. You're absolutely correct, but your statement was very incomplete.
