Roger said:
"Number of platters only addresses the TPI (tracks per inch) portion of areal density. "
Number of platters has nothing to do with tracks per inch. Tracks per inch is exactly that. On a typical 3.5" disk, we use from about .86" to 1.76" radius, give or take. Tracks per inch is the number of tracks we have for every inch of radius, so for a drive that has, say 6000 tracks, average tpi is 4000/(1.76-.86) = 6.67Ktpi. I say average because the actuator travels in an arc, which makes actual tpi vary with radius.
"Thus even with the same number of platters, the drive has higher areal density, thus higher performance. Yes, the GB/platter is the same, but SEG still has higher areal density."
This would only be true if Seagate is "short-stroking" the drive, thus using less of the usable area of each surface (the outside, where performance is higher), and making up for the capacity loss with greater areal density. This is not a common technique, and I'd be surprised to find out they're doing this. Do you have confirmed information?
Keep in mind that areal density is bits per square inch. Assuming brand A's platters use the same number of square inches as brand B's, and both have the same capacity per platter, they both have the same average areal density.
However, it's also possible (and likely) that a given areal density was achieved with a different combination of track and linear bit density (bpi) on brand A than brand B, and therefore has different performance characteristics. Furthermore, achieving a given areal density with greater linear bit density and lesser track density would likely give greater performance. Is this what you were trying to say? |
