faster spinning drives, while the data density may be a little lower due to the speed, is able to access data far faster (seek time) and because of the high rotation speed the sustained transfer rate is vastly better.
burst speed is not so dependent on disk RPM, being more dependent on the size of the ram buffer (most modern ata10 drives have 2mb) and the ata100 interface.
to put it in real terms i have a 16.8GP and a 60GXP 5400rpm vs 7200rpm
both on an ata33 for the moment, and due to the increased disk speed the seek times are reduced by 2-3ms and the sustained data transfer rate of the 7200rpm actually maxes out my ata33 interface
"Don't be too proud of this technological terror you have created"~Darth Vader, Star wars
You can probably fill your RAID-100 controller with buckets of 5400rpm disks, and never be able to get to that 100Mb/s limit. So why not spend the extra two pennies on drives that kick butt (Dare I say IBM ?)
then why does the 5400 say ata100 if it will never reach 100mb/sec?
The 100Mbs refers to the <i>interface </i>that the drives can connect to. Whether you have 1 drive or 4, they can connect to an interface with a capacity of 100Mbs. No drive on the market can sustain even half of that on its own, but use RAID and you might be able to get close with 4 of them (you lose some efficiency as you group them together, so 4 drives that can do 30Mbs will not give you 120Mbs even if the interface could handle it).
Have a look on Tom's site under the Storage area, and look back to when the IDE Raid cards came out (Promise did the first ones). Tom did some reviews on what you can expect from a set of IDE drives running RAID.
On a separate note, the drive speed does mean better performance, but only for the same spec of drive. An older 10Gb drive running 7200 will be beaten by a newer 60Gb 5400 drive, 'coz the data is packed closer on the platters, which means the head doesn't have to travel so far to read the same amount of info.
Check out the WD new 5400 drives that have 30Gb platters (WD300AB & WD600AB). These are very close to the best 7200 drives for performance, and are cooler and quieter in running (due to the slower spin speed). The performance is made up by packing the data in tighter. For reference, the fastest are the IBM deskstars which are 15Gb and 20Gb per platter depending on model.
Any ATA/100 drive CAN hit 100, but only in a burst. There IS a difference between a 5400 RPM ATA/66 drive and a 5400 RPM ATA/100 drive. If a drive can't hit 100Mbs during testing, it can't be labeled as an ATA/100 drive. Now of course, testing is done under optimum circumstances, something that we'd never see, cause we're too busy playing games. And that's ok.
Apple? Macintosh? What are these strange words you speak?