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2M BIOS extension for PC/XTs

Anonymous Coward

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I was a little skeptical about this at first, but while looking for information on high density controllers I stumbled on a conversation about a BIOS extension for PC/XTs that allows you to use high density (1.44, 1.2MB) diskettes in systems that equipped with floppy controllers that support the higher rates. Apparently it works with the 16-bit AT controllers that support 8-bit mode. The program is called 2M, and it comes with a TSR called 2M-XBIOS. It looks quite promising. I do not have my XT with me for testing, but I was hoping someone else could. While this method would not allow for booting from 1.44meg drives, I still think it would be quite practical for people who cannot find the HD controllers with BIOS.

Below is some information I found from the newsgroups:



Try the 2M30.ZIP utility. This program is mainly for formatting 3 1/2 disks to
1.88M extended format (1.5M for 5 1/4 inch). But it has a utility for BIOS
extension that is supposed to support the new drive formats on old PC:s. these
utilitys are named 2M-ABIOS and 2M-XBIOS.
Another utility in the same package is 2MX. Maybe something in this package
will work.
You can get 2M from:

FTP Address (Country) Directory Files
------------------------- --------------------- -------
ftp.gui.uva.es (Spain) pub/pc/2m 2m*.zip
oak.oakland.edu (USA) SimTel/msdos/diskutil 2m*.zip
garbo.uwasa.fi (Finland) pc/format 2m*.zip

-------------------- excert from the info file in 2M -----------------------

Although 2M was initially designed for AT and above computers, from 1.2
release it has gone with a PC/XT release: 2MX. The unique requirement is that
system must be equiped with high density diskette controller and drives. Some
modern small subnotebook computers are ready to connect an external high
density disk drive. Other relatively recent PC/XT systems are provided with
high density drives and a BIOS with high density support, but the disk drive
is a double density one and user can replace it. Finally, in oldest systems
which aren't classified in any of these categories, their owner can replace
both the double density drives and controllers with new high density ones;
this hardware may be used in the future in a new AT system (so, it is a very,
very cheap option and also a good investment).

Since it is difficult to find in the market nowadays high density
controllers for PC/XT systems, if needed, the user can install an AT one. In
2MX tests, I needed to insert a 16 bit card in a 8 bit slot. The card was a
IDE multi-io; however, the high half of bus (which can not be inserted since
the slot is a 8 bit one) is only used to access IDE hard disk, and can be
disabled by a jumper although this also was unnecessary. The logic for
diskette drives, serial and parallel ports was completely functional, since it
only uses the low half of slot.

The main problem is located in PC/XT BIOS, in 99% of cases it is not
capable to support high density. The solution in these systems is to load a
more modern BIOS helped by 2M-XBIOS.EXE, the terminate and stay resident
program which emulates AT AMI BIOS in XT computers. In fact, 2MX requests the
user to install this driver when it can't detect diskette drive types (this
is normal when BIOS is old and don't report diskette types). However, in some
modern PC/XT systems perhaps 2MX will be loaded without needing 2M-XBIOS. If
in this case there is some malfunction in drives, try to also load 2M-XBIOS.

2MX and 2M-XBIOS need a IBM compatible machine; I can say that both
programs have been tested in an original IBM PC 4.77, in a PS/2-30 8086 system
and at the moment are in service in some oriental clones. As it usually
happens, some trademark PC/XT systems are not sufficiently compatible; also,
some systems have diskette drive controllers in the motherboard, which can't
be replaced. You only can be sure that your system is compatible after trying
2MX and 2M-XBIOS; the 2M author can't know this before and also can't do
anything if system is not compatible. If your system is an oriental clone it
is almost sure that will be sufficient compatible; if it is a trademark one
(except IBM) it might not to be.
 
I tested this program out in my XT and it works beautifully. It takes about 4kb of conventional RAM to emulate the floppy functions of a 1993 AMI BIOS. Highly recommended to anyone who can't get their hands on a high density floppy controller.
 
I don't follow; what exactly did this TSR allow you to do that you couldn't before? Please be specific.

An IBM XT or PC will not format 1.44mb disks as 1.44mb using a standard romless floppy controller (aka no bios on the card)

using this utility you can take a standard generic 16bit ide multifunction floppy card, disable the ide and put it in your XT and format and use 1.44mb floppy disks as 1.44mb floppy disks as opposed to the normal 720kb limit imposed by the rom bios.

Got it? 1.44mb capability in computers that don't support 1.44mb drives at all.
 
I have been using this driver on a ROM-less high density floppy controller. I can report that it does give me access to 1.44MB disks in my 1.44MB drive. Before it would just say general failure when reading the disks because of lack of BIOS support.

The only problem I am having is I cannot format the disks using DOS 6.22. When I try it tries to format it as 360k! When I try to "format /f:1.44" it says drive does not support parameters. I am loading 2m-xbios with the switches "a:4 b:4" that should mean I am using 2 1.44MB disk drives. Maybe dos detects the drives in early boot and 2m-xbios can't or just doesn't update dos?

I would like to try other programs that to the same thing if there are any.
 
So this will let you boot 1.44M diskettes on an XT? Probably not...

On the other hand, if you had a ROM-able BIOS and a legacy 16-bit hard/floppy controller with an onboard ROM for the hard disk section (say, a SCSI or ESDI card), you could substitute a floppy BIOS there, since you won't be using the 16-bit hard disk section anyway.

The problem with diskettes using nonstandard formats (see XDF and DMF for earlier examples) is that you'll only be able to read them in systems equipped with software to do so.
 
I can still only boot with 720k disks. I can't even use a 1.44MB disk formatted to 720k because none of my disk drives like to do that. They all say track 0 bad when I try to do that.

I have a few 720k disks but even they are kind of flaky in my HD drives (I have no 720k only drives.) Only one of 5 720k disks was able to format w/o errors. And they will not format at all on my USB 1.44MB disk drive. Sorry I am drifting off topic now.

On the other hand, if you had a ROM-able BIOS and a legacy 16-bit hard/floppy controller with an onboard ROM for the hard disk section (say, a SCSI or ESDI card), you could substitute a floppy BIOS there, since you won't be using the 16-bit hard disk section anyway.

I plan on doing some experiments with this approach as soon as some eproms I ordered come in.

In the mean time 2m-xbios and a 720k disk or two should keep my XT clone going until I get BIOS support for 1.44MB again. I have no HDD btw.
 
I've never personally used MS-DOS 6.22, so I don't know what the issue is there.
I use either PC DOS 2000 or DR-DOS 7.01. As far as I can tell the format command with XBIOS works fine with both of them.
 
You know, if you have an XT-style controller with a digital (i.e. WD9216) separator, it should be a matter of a few cuts and jumpers to make the thing understand DSHD floppies. After all the 8272/uPD765 FDC in these things was designed originally for 8" drives. So, you'd need only to tap the read/write clock a bit upstream, since the 765 FDC uses different clocks for processor and floppy interface.

The earlier 5150 FDCs with their hybrid data separators are probably not a good candidate.

Just ruminating, here.
 
I have this very setup in a XT clone I put together Frankenstein style. A 16 bit floppy/IDE card with the IDE side disabled installed in a DTK TIM-TB10 motherboard. The extension needs to load before the 1.44 floppy becomes usable, so no booting from the 1.44 drive. Mine is setup using a 5.25" 360K drive as A: and the 1.44 drive is B: as I mostly wanted the drive to make getting software loaded on the machine easier. I have had no issues with this setup, either in 10 MHz mode or 5 MHz mode, but I have not tried to format a HD disk in the drive. Now I have an excuse to dig the computer back out and try it.
 
Pity it can't be set to use a secondary FDC address?

And, I just can't seem to load the driver without "+ Syntax error: execute from DOS command line to obtain help."

My config.sys line is:

DEVICE=2M-XBIOS.EXE A:3 B:1 C:1

Perhaps a third drive is not supported, despite me reading somewhere that up to 4 drives are supported?

It's also the only line in my config.sys file at present.

.....................Okay, it appears that only A: and B: are supported!?
 
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