720k 5.25 disks

[John Hood]

In article <196500031 at trsvax> uhclem at trsvax.UUCP writes:
>[In some article about three days ago, I (John Hood) wrote:]
>R3>The IBM startup test does not bash heads against stops, at least on
>R3>the AT; it only recalibrates and steps to track 34.
>
>Hmm, well it does it on the true-blue ATs we have here with 40 track drives
>in them. (Since the high cap drives have more than 40, no problem.)
>Our friendly IBM rep explained it away as I described.  I even recall that
>someone took a peek at the IBM BIOS listing to confirm that it wasn't just
>DOS doing this stunt.

Well, I looked at the BIOS listing in the back of the true-blue IBM
Tech Ref manual, and it only steps to track 34.  However, now that I
look at it a bit more closely, you're probably right: it may be
double-stepping the drive.  I've never seen or used an AT with a 360k
drive as drive 0, and it isn't a good idea to have one set up that way
when the clock/CMOS battery goes dead.

>R3>This BIOS trick will only work if the machine uses dual-speed 1.2M
>R3>drives.  The more common case of single-speed drives and floppy
>R3>controllers with three different clock rates won't work with this
>R3>trick; the data will get written at the wrong clock rate.  
>
>In his case, he was able to read cylinder 0 correctly, so the transfer
>rate was not the issue, and he already stated an AT environment which
>would have a dual speed adapter.

The comment wasn't aimed at Earl's machine, or Tandy's, but rather the
typical AT clone.  Other people reading this might get confused.
Earl's AT&T 6300+ is not a typical IBM clone.

  --jh


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