[NTLUG:Discuss] OT: SCSI hard drive sizes...

[steve]

Robert Pearson wrote:

> All SCSI, both parallel and serial (SAS), spin 2x faster than SATA, have
> much more rugged construction, are dual-ported, have longer MTBF and
> longer warranties (5 yr vs. 1 yr for SATA).
> All of which cost money.

When the drive platter spins more rapidly, each magnetic 'bit' has
less time to induce a voltage in the drive head.  In order to get
enough signal from the head for the electronics to detect, the bits
have to be physically larger so they spend more time under the drive
head.  Larger bits mean less of them.

(Actually, it's probably more due to the duration of the voltage than
the amount of voltage...but you get the idea).

Hence there is a straight trade between speed and capacity.  You double
the speed - you halve the capacity.

I presume that some marketting person decided that SCSI buyers are
more interested in performance than capacity - with the reverse
being true for PATA/SATA buyers.