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From: perry@ccssrv.UUCP (Perry Hutchison)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Three Floppy Drives on an XT
Message-ID: <714@ccssrv.UUCP>
Date: 6 Oct 89 03:12:11 GMT
References: <1642@jolnet.ORPK.IL.US>
Reply-To: perry@ccssrv.UUCP (Perry Hutchison)
Distribution: usa
Organization: Control-C Software, Inc., Beaverton, OR
Lines: 41

In article <1642@jolnet.ORPK.IL.US> himage@jolnet.ORPK.IL.US (Steve Schwartz)
writes:

> Has anyone out there ever installed, or heard of a way
> to install three floppy drives in an XT computer, two 
> 5.25" drives, and one 3.5, 720k drive.
> 
> If so, how can it be done, as far as I know, the XT can only
> accept two florry drives, or two floppy drives, and a tape
> drive on the floppy cntroller.

As far as I know, an IBM XT uses the same floppy controller as the IBM PC,
and that controller supports two internal drives plus one or two external
drives.

Each drive cable can handle a maximum of two floppy drives.  (I don't know
how the tape drive is connected -- that's something that got added on later,
and not by IBM.)

A four-floppy-drive controller allows for two drive cables.  In the IBM PC
(and I believe also the XT), the cable for the internal drive(s) connects
to an edge connector on the controller card and the cable for the external
drive(s) connects to a 37-pin D-connector on the controller's mounting bracket.

Of course, some clones may have left off the external connector, but before
giving up you might look for a second internal connector on the controller.
This would be for a 34-pin ribbon cable.  It might be either an edge
connector (like IBM used for the internal drives) or a 34-pin header like
that often used for hard disks.

While we're on this subject, it is also possible to attach additional floppy
drives to an AT.  For an IBM AT, this is a bit more involved than for the XT
since the AT's combined hard/floppy controller lacks the circuitry to support
more than two floppy drives.  Because of this misfeature, when the PC
Convertible came out and IBM needed to allow for an external 3.5" drive, they
had to design an adapter card (which takes up a slot!).  It also connects
into the ribbon cable between the controller and the internal floppy drives,
and provides the missing circuitry and 37-pin external-drive connector.

Some clone combination hard/floppy controllers have this done right: they
include support for four floppy drives directly on the controller card.