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From: wilker@gauss.math.purdue.edu (Clarence Wilkerson)
Newsgroups: comp.os.os9,comp.sys.m6809
Subject: Re: adding as disk drive to COCO3
Message-ID: <4192@mentor.cc.purdue.edu>
Date: 22 Jan 91 02:37:55 GMT
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Reply-To: wilker@gauss.math.purdue.edu.UUCP (Clarence Wilkerson)
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Sorry to contradict the last posting, but 1.2 meg drives
intended for IBM AT clones do spin at 360 RPM, with a
data transfer rate of 300 K-bits per second, instead of
the standard for older 5.25" drives of 250 kbs.at 300 RPM.
  Notice that if you write a disk on a drive at 250 kbs at
300 RPM, the bits have the same density as 300 kbs at 360 RPM.
So diskettes written either way or interchangeable at the
standard double density.
  However, when writing a 15 sector HD disk, the AT uses
a data rate of 500 kbs, which is not quite twice the double
density rate.
  Finally, the 1.44 meg 3.5" drives also use 500 kbs at 300 RPMs
to pack 18 sectors on a track instead of the 9 at lower speed.
Clarence Wilkerson