Difference between IDE and SCSI ??

Lamar Owen lowen at pari.edu
Wed Feb 6 10:57:54 UTC 2008

On Wednesday 06 February 2008, Les Mikesell wrote:
> Tim wrote:
> > On Tue, 2008-02-05 at 11:07 -0600, Les Mikesell wrote:
> >> The disk size is another hint. Scsi drives would be 36 Gb, IDE's 40.
> >
> > Hadn't noticed that before.  What's the reason?
> I don't know why, but most scsi drives run:
> 9, 18, 36, 72, 146, 300 gig
> where most IDEs are
> 10, 20, 40, 80, 100, 160, 320.

10K RPM drives have smaller platters than the typical 3600/4200/5400/7200 RPM 
drives, and thus fewer cylinders.  The same thing is true of the WD Raptor 
line that are based on 10K RPM SCSI drive technology; ever noticed their 
capacities line up with the typical 10K RPM SCSI drive capacities?  15K RPM 
drives have even smaller platters, but, since users of SCSI drives are used 
to the capacities in multiples of 9GB (give or take a few tenths of a GB), 
the 15K drives are typically the same.

Although there are other sizes in the SCSI realm.  I have a few 50GB Seagate 
Barracuda SCSI drives (full height 3.5 inch) and one or two Elites; the Elite 
23 and the Elite 47 were at one time the capacity kings in the 5.25 inch full 
height form factor at 23 and 47GB, respectively.  The two Elites were 
identical except for the number of platters; the 47 of course had double the 
number of platters than the 23.  I have a couple of 11GB full height 5.25 
UW-SCSI drives, too.
Lamar Owen

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