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From: brown@nicmad.UUCP (Mr. Video)
Newsgroups: comp.sys.ibm.pc
Subject: Re: IBM 3.5 Drives
Message-ID: <2065@nicmad.UUCP>
Date: Sun, 11-Oct-87 23:08:26 EDT
Article-I.D.: nicmad.2065
Posted: Sun Oct 11 23:08:26 1987
Date-Received: Tue, 13-Oct-87 05:43:57 EDT
References: <2262@tekigm2.TEK.COM>
Reply-To: brown@nicmad.UUCP (Mr. Video)
Organization: Mr. Video's Hangout
Lines: 96
Keywords: 360k vs 720k

In article <2262@tekigm2.TEK.COM> wrd@tekigm2.TEK.COM (Bill Dippert) writes:
<Apparently it is a bug, I ran into the same problem when I set up my XT with an
<external 3.5" drive.  I have for my configuration:
<
<     first 5.25" drive A:
<     second 5.25" drive B:
<     3.5" drive C: (360K for format purposes)
<     hard disk D:
<     3.5" drive E: and F: (720K for all purposes)
<
<     (Don't ask why I made the hard drive D:, however, I thought that C: would
<     work ok for the 3.5", but due to the bug, it does not.)
<
<     Now, as to the bug:  note that I said that you cannot format disks using
<     C: drive for anything other than 360K.  For all other purposes drive C: is
<     720K, only when you try to format blank disks does it think that it is a
<     360k drive.  Why is beyond me.  However, per IBM instructions, I set up
<     two more disk drives as E: and F: (using the same 3.5" physical drive).
<     These perform perfectly as 720K drives.  To do this, you need to setup in
<     your config.sys file a statement --
<     DEVICE = \DRIVER.SYS /D:2 /T:80 /S:9 /H:2
<
<     (One of these will set up E:, two of them will set up E: and F:.)
<
<     Apparently the default for the 3.5" disk is T:40, but there is nothing
<     that I can find that shows how to change this default.  I thought that the
<     device = statement would do this, but then I discovered that all it did
<     was setup more diskdrive letters using the same physical drive.  The whole
<     thing is ridiculous, another IBM "feature".  (The other possibility is
<     that the default is D:1.)  T - track and D is single/double side disk, I
<     think!
<     I hope this helps, IBM's data sheets sure do not.

You have not run across a bug.  Let me explain a little something and then
the pieces will fall into place.  But, before I say that, I better say that
my PC-XT is set up as the following:

	two 5.25" floppies as A: and B:
	two 3.5"  floppies as C: and D: (360 K)
	              also as G: and H: (720 K)
	two 20MB hard drives as E: & F:

The IBM PC and XT use the switches to tell it how many floppies are attached.
The BIOS only understands these as 360K drives.  Any hard disks are then added
after that.  In order to use 720K floppies externally, you MUST switch in
more than two floppies.  If you are using two 720K externals, like me, you
MUST switch in four total floppy disks.  The IBM program, DRIVER.SYS, will
only allow you to attach to drives that exist.  So, for external drives,
three or more must be switched in at boot time.  The DRIVER.SYS program only
makes a new logical drive out of an old physical drive.  It cannot turn
drives A, B, C or D directly into 720K units.  They will always be 360K
drives.  Only when addressed as the new logical drive, will the 720K options
become available.  You can put as many logical drives against a single
physical drive as you like.  If you have only one 3.5" external floppy,
then I do suggest making it two logical drives, so that you can do a
diskcopy (it will tell you to swap diskettes).  Yes, a diskcopy will let
you copy onto itself, but a COPY will not.

Because the BIOS only understands drives A through D (if floppies) as being
360K, they can never be formatted as 720K floppies.
The author gave the following line for the CONFIG.SYS file:

     DEVICE = \DRIVER.SYS /D:2 /T:80 /S:9 /H:2

But, it only needs to be:

     DEVICE=[drive:][path]DRIVER.SYS /D:n

The default is 80 tracks, 9 sectors and 2 heads.  The /D:n is replaced with:

	/D:0 for drive A:
	/D:1 for drive B:
	/D:2 for drive C:
	/D:3 for drive D:

For /D:0 and /D:1, the internal floppies have to changed to 3.5" floppies
and for /D:2 and /D:3, the external floppies have to be changed to 3.5".
For my situation I have two lines, one with /D:2 and one with /D:3.

In our engineering department, I set up all PCs with 4 physical floppies,
even if there wasn't any connected externally, just in case we wanted to
attach something in the future.  Changing the software on the hard disk
from C: to E: isn't very easy, when done later on.  Plus you many not
remember all the places that it may be set to C:.  That proved it to be
a wise decision, as mine and a couple of other PCs now have 3.5" floppies
on them.

I do agree that it would have been nice if IBM could have written a TSR that
would have taken over the BIOS operation so that C: or D: could have been
720K drives.  But, that TSR would have taken up precious memory.  They way
it works now really isn't a problem.
-- 
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