rl@cbnewsl.att.com (roger.h.levy) (10/28/90)
About 2 years ago, I purchased a Compuadd 286/10 for a lab at work.
Although I ordered the 40 Mb disk option, the system appeared to be
delivered with a 30 Mb disk. I tried to fdisk and made a few other
feeble attempts to search for an additional 10 Mb but other concerns
and a relative disk space surplus quickly made me forget this issue.
Last week, said computer suffered a CMOS parity error. Having never
fiddled with CMOS (it was set by Compuadd), I rummaged around for
the system's documentation in order to find the drive type. The disk
is a Miniscribe 3650 and the Miniscribe manual specified it as drive
type 3. The prompts from the CMOS maintenance program indicated that
drive type 3 is 30 Mb (615 tr, 4 surfaces, precomp = 300). Suspecting
that setting up the 3650 as this type was originally responsible for
my lost disk space, I scrolled through the drive type entries looking
for one that matched the 3650. The only apparently matching entry
was drive type 32 (809 tr, 6 surfaces, precomp = 128). After sel-
ecting this type, I was able to recover the long missing 10 Mb.
This leads me to ask the following questions:
1. Are drive types standard? Where is the definitive reference?
Do they differ from bios to bios?
2. Is the 3650 type 3 or 32? Is the manual (type 3) or the bios
(type 32) or both or neither correct?
3. What affect did precomp = 300 rather than 128 have on my drive?
4. Should I worry about the drive? Can I rehabilitate it? It
seems to be working and I gave it a LL format with Spinrite.
Thanks in advance.
Roger Levy
rl@groucho.att.compaulg@bhpmrl.oz.au (Paul Gallagher) (10/29/90)
Ah! The omnipresent 3650! This disk's a bit of a maverick as far
as getting the system configured is concerned. The IBM AT CMOS
drive table contained 15 entries. It sounds as though Miniscribe
took the easy path and documented the 3650 as type 3 because (even
though the parameters don't match properly) its the nearest match
you'll find!
The first 15 entries of the drive table on most machines match
the original AT table, but additional entries are generally
proprietary. The bottom line is that the 3650 doesn't have a
standard type number.
Regarding precomp: 300 is actually the documented pre-compensation
for the 3650. This is the cylinder that the write current is stepped
up in order to account for the shorter linear sector size as you
approach the centre of the disk. Starting the pre-comp further out
(i.e. at 128) thus shouldn't have an bad side-effects (whereas a
higher pre-comp could have exposed you to data corruption problems.
Hope this has been of some help.
Regards, Paul.
/\/\ Paul Gallagher, PC Support Officer,
/ / /\ Computer Systems Group,
/ / / \ BHP Melbourne Research Laboratories
/ / / /\ \ 245 Wellington Rd Mulgrave Vic 3170 AUSTRALIA
\ \/ / / / Phone : +61-3-560-7066, Fax : +61-3-561-6709
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