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From: slsw2@cc.usu.edu
Newsgroups: comp.os.cpm
Subject: re: Using 3.5" floppies instead of 8" floppies
Message-ID: <1991Feb11.092925.46847@cc.usu.edu>
Date: 11 Feb 91 15:29:25 GMT
References: <11375@uhccux.uhcc.Hawaii.Edu>
Lines: 28

In article <11375@uhccux.uhcc.Hawaii.Edu>, ralph@uhheph.phys.hawaii.edu (Ralph Becker-Szendy) writes:
> Since someone asked what the method is to hook up a 3.5" floppy disk drive
> instead of an 8" drive, here is a listing of pin-numbers on the cables. A 5.25"
> HD or 3.5" HD floppy is electrically nearly equivalent to a 8" DD floppy. The
> only major difference is that some 5.25" HD and all 3.5" HD floppy drives spin
> at 300RPM (instead of 360RPM, what it used to be for 8" floppies), so you can
> pack more data onto each track (but you don't have to). Some 5.25" HD drives
> switch to 360 RPM when switching to HD mode though (usually jumper selectable).

Actually, there is a major difference between 3.5" and 5.25" that I came 
across in a floppy controller data sheet that probably explains why my attempt
to replace the 8" drive on my system failed miserably; I've not tried again
using the new information, so I can't say if that's the problem.

3.5" drives use CMOS drivers for the signals that they drive, and therefore
cannot drive the terminators generally used for 5.25" and 8" drives. The
data sheets for the Intel 82077A therefore recommend that if you are going to
mix 3.5" drives with 5.25" drives, you include a buffer between the 3.5" and
5.25" drives so that the drive doesn't have to try to drive the 5.25"
terminator.
-- 
===============================================================================
Roger Ivie

35 S 300 W
Logan, Ut.  84321
(801) 752-8633
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