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From: paula@bcsaic.UUCP (Paul Allen)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Using 8 inch floppies on an AT compatible
Message-ID: <2081@bcsaic.UUCP>
Date: Fri, 4-Sep-87 20:47:39 EDT
Article-I.D.: bcsaic.2081
Posted: Fri Sep  4 20:47:39 1987
Date-Received: Sun, 6-Sep-87 03:21:32 EDT
References: <2211@batcomputer.tn.cornell.edu> <777@custom.UUCP>
Reply-To: paula@bcsaic.UUCP (Paul Allen)
Organization: Boeing Computer Services AI Center, Seattle
Lines: 46
Summary: I think it will work



In article <777@custom.UUCP>, boykin@custom.UUCP (Joseph Boykin) writes:
>In article <2211@batcomputer.tn.cornell.edu>, sparks@batcomputer.tn.cornell.edu (Steve Gaarder) writes:
>> I'm looking for a way to connect a Shugart SA810 half-height single-side
>> 8 inch floppy to an HP Vectra (AT compatible) for the purpose of reading
>> standard CP/M disks.  Two questions:
>> 
>> 1) Hardware:  Since the high-density drive uses the same data rate as an
>> 8 inch drive, can I hook up the drive to the existing controller?
>
>Data rate has little to do with the problem.  As a simplistic answer,
>the two cables are different (8" drives have a 50 pin connector, 5 1/4's
>have a 34 pin connector.  Although I haven't ever looked into
>this, I doubt very strongly if there is any way to simply reroute
>signals so the two would be compatible.  The real answer is that
>the two drives are not compatible with each other.

[stuff about PC 8" controllers and CPM deleted]

Actually, it should be very simple to do this, provided that you don't
mind building an adapter to match signals between the 34- and
50-conductor cables.  All of the signals that matter are identical on 8"
DSDD and 5.25" DSHD AT-style drives.  The floppy controller in my Z100
can handle both 5" 360K and 8" 1.2M drives.  I am planning to add a 1.2M
5" drive to use for backing up my hard disk sometime soon.  I have been
told that this has been done by other Z100 users.  You will need good
technical documentation on both the 8" and 5" 1.2M drive interfaces.
The IBM AT Technical Reference might do for the 5" drive, but it fails
to document the signal that switches the drive to high density mode.
I have had conflicting information about this signal from several
sources, and don't want to pass along misinformation.  Possibly the tech
ref for one of the AT clones would be a better source?

Once you get the drive hooked up, you should be able to format it as if
it was a 5" DSHD drive.  Getting it to talk to CP/M diskettes may be
tricky, since the diskettes will lack a proper media descriptor byte and
the BIOS will not be able to tell what kind of floppy it is.  Not having
tried this myself, I think I'll keep my mouth shut about how hard I
think your task will be.  (My machine doesn't have a BIOS like the PC
does.  Maybe some PC hackers out there would care to comment?)

Good luck!
Paul Allen
paula@boeing.com
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