IBM PC-DOS 7.x on USB Key

Can't believe I found this group of people interested in DOS and boot....never thought it existed, after weeks of searching.

I've tried for weeks to boot PC-DOS from a 64 MB USB key. I've had some success, but my goal is to boot DOS in USB-FDD format with more than 1.44MB.

I'm been using the HP-format utilitiy and WinImage and various other command-line utilities to manipulate boot sectors, MBR, etc. But for some reason I can't get to my ultimate goal.

I'm using a genuine IBM USB key, one of the first ones made, way back. I remember paying a lot of money for it, I think around $65 for 64MB. Its actually quite a nice key in that it is very flexible. I can put just about anything on it, floppy boots, MBRs, linux, and all the tools I've tried, can write to it without problem.

It even comes with its own Boot utility that creates an IBM DOS 7.1 bootable key with full capacity of 64MB. But this will only boot on machines that see the USB-key as USB-HDD.

But plug it into my PC which sees the bootable key as A: and it will fail with the message "Starting IBM DOS......' . I think this means that it did actually boot and its now into the IBMBIO.SYS program, but why doesn't it finish?

If I zap it with a 1.44 MB image, then it will boot IBM DOS 7.0 with no problem. But is only 1.44MB....Yuck!

Here is where I get totally baffled! I have an image of a MSDOS 5.x (From Win98, I think) and its 32MB. If I zap this image onto the usb key, (using the HP-Utility), it will format and boot as A: drive, just fine without any issue. And I can see 32MB. So, why can't I do the same thing with IBM DOS 7.0.???

I've compared the boot sector codes (between the MS-DOS image and the IBM-DOS image and they are virtually the same, so I got to believe the code in the DOS boot programs (IBMBIO.SYS or IBMDOS.SYS) somehow detects or checks that if it is running from A: and then maybe makes assumptions about FATs or disk sizes, and maybe that it must be 1.44 MB or 2.88 MB or someother standard floppy size. Wish I could confirm this somehow, without tracing through the dissassembly.

Can anybody shed some light on this?

To summarize, IBM PC-DOS will not boot on a machine that insists on seeing only USB-FDD formats with anything other than 1.44MB image. I'd like to create an IBM DOS 7.x image that boots larger than 1.44 MB as A: drive for BIOS's that only see USB keys as floppy.

Hope I gave enough info and someone can help. thanks.

Rather obviously PC-DOS is a less common OS, thus you'll have to fill a lot of gaps.

There are several possible paths to explore to find a suitable way to have that thingy booting.

Choose one:

• makebootfat
• grub4dos
• fbinst
• PLoP

And let's start with it.

Which OS are you running normally?

Can you provide an image of the first 64 sectors of the stick when the PC-DOS 7 is applied and of the first 64 sectors of it whern the DOS 5.0 (I presume that it is actually a DOS 7.x from Win9x, that may have the DOS 5.0 tag in the bootsector) is applied?

Please compress these images in a .zip and attach it to your next post.



Wonko

Ok, I will do that, as soon as I get home tonight, so you may not see it until tomorrow.

I started down these paths you suggested, but only since yesterday, thanks to this site. Actually, I did run into makebootfat a while ago, but did not have much luck with it and gave up. Most of the time I was just zapping values into boot sectors trying to change things, but I really didn't know what I was doing. I think a more logical approach using proper tools and a community of interested people is a much better approach.

The frustrating part is that I always believed the IBM PC DOS and Microsoft DOS were enough alike that if one works, the other should work too. But maybe that's not the case!

After reading a lot on this site, I am starting to believe its just a matter of disk geometry and the Boot program not being in sync. Hopefully we can figure this out. thanks.

To keep you entertained, a lesser known resource about the oddities of (FAT) bootsectors:
http://homepage.ntlw...name-field.html
More:
http://homepage.ntlw...eter-block.html
http://homepage.ntlw...fat-widths.html
http://homepage.ntlw...ystem-type.html

If you want to do another round with makebootfat, you might find this post interesting:
http://www.911cd.net...o...13784&st=44



Wonko

Ok, in the attachment: first 64 sectors of bootable USB images as follows:

1) format-with-IBMKEY.bin - used IBMKEY utilitiy program to create bootable IBM DOS 7, 64MB, boots as C: drive on most machines, will NOT boot on USB-FDD machines

2) format-with-HP-FreeDos-50MB.bin - used HP utility and 50MB image downloaded FreeDOS floppy image. Boots on USB-FDD as A: drive and 50MB.

3) msdos-32mb.bin - used WIN98 to format USB key, boots up as A: drive on USB-FDD machine.

4) ibmdos-32MB - used IBMDOS 7, FORMAT command on USB that used to have the previous image (msdos-32mb.bin). Boots up on USB-HDD type machine, but fails on USB-FDD type machine.


summary, 2 and 3 will boot fine on my USB-FDD bios based machine, but neither is IBMDOS.

1 and 4, boot as IBM DOS, but only on machines that see USB-HDD devices.

I also have a 1.44 MB image of IBM DOS, that boots, but that is seems to be FAT12 format and probably not interesting for debugging. Let me know if you want to see it.


Let me know if you see anything obvious or you have some suggestion as to what I can try. thanks.

NO.

What you posted is not what I asked for/does not make much sense.

There is either a misunderstanding or you used some strange procedure, it is not clear under which OS you ran the various tools.

All the attached files have as first sector a bootsector (or PBR).

Besides, each of them has a "random" number of "hidden sectors" or "sectors before".

More exactly:
1) format-with-IBMKEY.bin - 5 hidden sectors/HS geometry 32/5
2) format-with-HP-FreeDos-50MB.bin - 0 hidden sectors/HS geometry 255/63
3) msdos-32mb.bin- 16 hidden sectors/HS geometry 8/16
4) ibmdos-32MB - 16 hidden sectors/HS geometry 8/16

The only values that make some sense are the ones of #2, which however CANNOT possibly be created by the "HP utility" (which main scope is EXACTLY that of writing a MBR as first sector of a device).

I presume that you are running some form of Windows (2K/XP/2003/Vista:ph34r:/2008/Windows 7) as you ran the "Hp utility".

Can you please confirm this, and state the actual Windows OS you are running/can run?

If you run any of those, get the dsfok package:
http://members.ozema...lifetv/freezip/
and run the command:

dsfo \\.\PHYSICALDRIVEn 0 0 NUL

as better detailed here:
http://www.boot-land...?...c=5000&st=1
and post the exact size you get as a result.

With these data I can try simulating your stick and see what can be done, and hopefully give you some files to experiment with.

The scope is NOT (as I see it) of having a key that boots as "HDD" but NOT as "FD", nor that of having a stick that boots as "FD" but NOT as "HDD", the scope is having a stick that boots BOTH as "FD" AND as "HDD".

BTW, but do not count too much on it , I found an old attempt I made to easen the use of makebootfat, that I am re-writing/reviewing, in such a way that should be usable relatively easily



Wonko

thanks for looking into this.

I did everything in WinXP SP2. Remember, the images I uploaded here were all turncated after 64 sectors, so you don't have the full images. Of course, I can upload the whole thing if you like. i just tried looking at one of them and it matches my full image. I used standard WinXP compressed folders, no other zip programs. Let me add more details about how I created these.


1) format-with-IBMKEY.bin - this image was created with a tool that came with the USB key. You can still find it on ibm site here: http://www-307.ibm.c...ocid=MIGR-46276
It creates a bootable key, but only on machines that see the USB as an HDD. It puts IBMBIO.COM, IBMDOS.COM and COMMAND.COM on the disk. when booted, it shows as IBM DOS 7.0 when I type the VER command at the command prompt.

2) format-with-HP-FreeDos-50MB.bin - this image was created with the HP format Utility, and using a free downloadable floppy image that is 50MB. (It was the closest to my 64MB key. The site has lots of image sizes, but I can't find the link right now, I'll post it later when I get to my bookmarks at home). This image has the standard FreeDOS boot files. This boots on my desktop as A: drive with full 50MB disk. But, I really can't use FreeDos for what I want to do.

3)msdos-32mb.bin - to be honest, I can't remember exactly how the image was created. It is an MS-DOS image, 32MB. I believe the image was created by capturing it from another USB key and saved using WINIMAGE. Then I zapped it onto my IBM Key using the HP Utility. It boots fine as a A: drive on desktop machine, but it is only 32MB and it is MS-DOS, I really need IBM DOS.

4)ibmdos-32MB.bin -created this by formatting a 32MB harddrive (using VMWARE) and capturing the image with WinImage and then zapping my 64MB key with it. It will boot on my laptop as C: drive, but fails on my desktop. It gets as far as saying "Starting PC DOS ......" and that's it.

Thanks again for working with me on this.

P.S. just saw a post on some other site that someone had problems getting IBM DOS to boot on USB key...but I lost the link!! Thanks for the links to discussion about :the oddities of (FAT) bootsectors:" very interesting and maybe related. I will investigating further.

Remember, the images I uploaded here were all turncated after 64 sectors, so you don't have the full images.

Yep, but you seem to be missing (on images #1, #3 and #4) the "hidden sectors" that are BEFORE the data you sent.
In other words, you imaged (HOW? With WHICH utility?) first 64 sectors of the LogicalDrive (whilst I wanted first 64 sectors of the PhysicalDrive).
For image #2 it doesn't make any difference, since there are 0 hidden sectors, the LogicalDrive and the PhysicalDrive are the same thing. (and yes, ONLY image #2 is actually partitioned/formatted "properly" as "supper-floppy").


Thanks for #1.

In point #2 we are evidently talking of two different "HP usb utoilities", or at least of a different usage of it.

The 50 Mb image you found, was most probably here:
http://bootcd.narod.ru/images_e.htm

But the HP utility we are used to refer to are the bolded ones (two different versions of the same utility, originally by A-DATA, if I remember correctly):

UTILITIES FOUND

About the second problem, there are a few freely available tools that supposedly work, the most used of which is the so-called HP USB UTILITY.

There are two versions of this utility for Windows:
(search for the relevant spxxxxx with Google or on HP site)

sp27213 HP Windows Format Utility for USB Drive Key or DiskOnKey
version 2.00.006 A (6 Feb 04)

sp27608 Windows-based Format Utility for HP Drive Key or DiskOnKey USB Device
version 2.1.8 A (17 May 04)
(substitutes 27213)

A DOS one:
sp27214 DOS-based Format Utility for HP Drive Key or DiskOnKey USB Device
version 1.00.012 (12 Jul 04)

And this one with Syslinux on it:
cp004934 HP Drive Key Boot Utility
version 7.11.3790.0 (14 Dec 04)

These two partition and format the USB stick (as opposed to "applying an image" to the stick).

Winimage, for a number of reasons that would be a bit too long to explain, while being a nice app, is NOT the right choice for USB thingies, so simply FORGET about it.

So, images #3 and #4 are "botched" since day one (though #3, being MS-DOS a bit more "tolerant" does work on some machines).

No surprise about #2 looking just right (as it is actually http://bootcd.narod.ru/fd050000.zip ).

I'll check the utility #1. Though it seems like being actually an IBM conversion of a manufacturer tool.

But still, I think that you should forget about them all and start again from scratch with the actual DATA (size) of your actual 64 Mb stick.

In the meantime, to add to your mental confusion , I released the makebootfat helper:
http://www.boot-land...?...c=10397&hl=



Wonko

P.S.: Should you not already be confused enough, some more data/info :
http://www.boot-land...?showtopic=3100

I gave makebootfat another try....thanks for the helper...it really did help to get it going. (did you know your .bat file, doesn't actually run the makebootfat at the end? See here,

ECHO.
ECHO %commandline%
GOTO :EOF
ECHO.
ECHO Are you sure....

So I just type the command manually...it was fine. Anyway, I tried the 'Dual' option with and without the 'Zip' option. In both cases, it tries to boot my IBM DOS, but stops at the 'Starting IBM DOS ....' message. The fact that it is actually booting into IBMBIO.COM means that it is booting, and all mbr and bootsecotrs are all in the right place, right? I'm thinking there must be some check inside the code that is either looking for sectors in the wrong place, or its checking for size of disk and doesn't like A: drive and disk size > 2.88, or some other check that it shouldn't be doing anyway. I'm going to look for a later version of IBM DOS, I think it was called IBM DOS 2000? I know I have the disks somewhere in the house. thanks again for all your help...

By the way, excellent use of DOS script language in your mkbt_fat.cmd. Good tutorial if anybody wants to write command language.

I'll keep reading your references...so much more to learn! Ciao!

Sure.

However you got the wrong snippet.
Try removing the GOTO :EOF and ECHO here :

GOTO :EOF
ECHO.
ECHO Are you sure you want to continue?
ECHO Type YES (Capital) or press [ENTER] to abort.
SET /P Confirm=
IF NOT %Confirm%.==YES. ECHO Program aborted by user&GOTO :EOF
ECHO %commandline%
ENDLOCAL
GOTO :EOF

And, just for the record it is NOT "DOS script language" it's NT batch language (you cannot run the batch under DOS/win9x/Me, as simply some commands aren't there, though there may be a workaround with an alternate batch interpreter).

The fact that it is actually booting into IBMBIO.COM means that it is booting, and all mbr and bootsecotrs are all in the right place, right?

Yes, it is possible that something else is blocking the stoopid IBM DOS from actually booting, but it sounds like we are a little step ahead in the right direction.

You need to make sure that with the SAME commands makebootfat makes the SAME bootable key with MS-DOS 7.x, then we can try some more tricks/check some more possibilities/hacks.

Wonko

Makebootfat does not respect seemingly Cylinder boundaries, that may be part of the problem.

An attempt:
try using the attached Makebootfat_IBM.exe instead of the original one.

This is a modified version by jaclaz that creates bootsectors with "IBM 2.0" instead of "MAKEBOOT" in the OEM name field.

That is "IBM"[SPACE][SPACE]"2.0", the reason is explained here:
http://homepages.tes...name-field.html


Will it work better?
Will it work at all?

Who knows.

Discussion topic is here:
http://www.boot-land...showtopic=10361

I need this info:

If you run any of those, get the dsfok package:
http://members.ozema...lifetv/freezip/
and run the command:

dsfo \\.\PHYSICALDRIVEn 0 0 NUL

as better detailed here:
http://www.boot-land...?...c=5000&st=1
and post the exact size you get as a result.

to try next attempt (respecting cylinder and head boundaries).



Wonko

Hey Wonko, thanks for your continued support! Got busy the last few days, but I'm back...

So this is what I tried:

Using your mkbt_fat.cmd, I can create an MS DOS bootable key that will boot as A: drive on my USB-FDD motherboard, full 64MB. (this is nice, some good, I only had a 32MB MS-DOS image before). However eventhough I used the -2 option, it did not boot on my USB-HDD machine. (no big issue here, I'm trying to get IBM DOS to boot, don't really care too much about MS DOS at this time.)

Using exact same process, I create a IBM DOS USB key,(of course I use IBMBIO.SYS and IBMDOS.SYS and an IBM DOS 7 bootsector), but it will NOT boot my USB-FDD or USB-HDD machines. So, no real progress here.

I ran the dsfo program against the makebootfat formatted key and interestingly, it goes into a continuous loop counting up to 1113MB. I killed the program at this point.

Then, just for fun, I format the USB stick with WIN XP format and run dsfo again, same thing, it just keeps counting up, way past the 64MB size of this key. So we can probably rule out makebootfat as problem formatter. (BTW, I know I'm directing dsfok to the right drive because the light flashes on the key while its reading.)

Now, I run the IBM Key Format program, format the usb key, same thing again, dsfok just keeps counting up past 64MB.....I suspect something not right with dsfok? or maybe my USB environment either with BIOS or WinXP ?

Tried everything again with makebootfat_IBM....same results.

What next? I would really hate to start putting in break points in IBMBIO.SYS...that could take forever, my Intel assembler skills are about 20 years old!!

Later...

It's the first report of this kind, it is probably a kind of incompatibility between dsfo and that particular key.

Are you sure you are using the right n in \\.\PhysicalDriven, don't you?

However, no problem.

Just run makebootfat again with the MSDOS files.

Use options:

-2 Bottsector.F16 <- a MS-DOS bootsector
-m mbrfat.bin <- the special MBR that comes with makebootfat
-F

Then run:

dsfo \\.\PHYSICALDRIVEn 0 51200 C:\msdos.bin

Then run makebottfat_IBM with the IBM files, again with the same paremeters above.

Then run:

dsfo \\.\PHYSICALDRIVEn 0 51200 C:\ibmdos.bin

Compress C:\msdos.bin and C:\ibmdos.bin in a .zip archive and post the .zip as an attachment to your next post.

This way I can check the actual geometry/size of the stick as makebootfat sees it.

Wonko

Ok, here you go.

Some details:

Here is the command I used for makebootfat for msdos.bin:

makebootfat_ibm -v -o usb -2 msdosusb.F16 -m mbrfat.mbr -F -c IO.SYS -c MSDOS.SYS -c COMMAND.COM dummy

Here is output from makebootfat:

device_start 0 [sectors]
device_size 127840 [sectors], 62 [MB]
device_geometry 7/255/63 [cylinders/heads/sectors]
bios_drive HDD
fat_start 63 [sectors]
fat_size 127777 [sectors]
fat_bit 16
fat_sectorpercluster 2

Here is output from dsfo:

E:\kdrive\Utilities\NewWinImage\dsfok>dsfo \\.\PHYSICALDRIVE1 0 51200 c:\msdos.bin
OK, 51200 bytes, 0.063s, MD5 = 137c6822ce533086c7864a70240ec9af

================================

Here I do it all agian with IBM DOS files:

makebootfat_ibm -v -o usb -2 formatted-w-IBMKEY.F16 -m mbrfat.mbr -F -c IBMBIO.COM -c IBMDOS.COM -c COMMAND.COM dummy

Output from makebootfat:

device_start 0 [sectors]
device_size 127840 [sectors], 62 [MB]
device_geometry 7/255/63 [cylinders/heads/sectors]
bios_drive HDD
fat_start 63 [sectors]
fat_size 127777 [sectors]
fat_bit 16
fat_sectorpercluster 2

Output from dsfo.

E:\kdrive\Utilities\dsfok>dsfo \\.\PHYSICALDRIVE1 0 51200 c:\ibmdos.bin
OK, 51200 bytes, 0.063s, MD5 = 49978c110583d4fa629673b60d8e64c7

=============================


thanks wonko.

Let's try with a different geometry (16/63).

Get the attached file.

Try restoring the two images, one at the time, by using dsfi:

dsfi \\.\PHYSICALDRIVE1 0 0 c:\ibm64kbD.img

And see if any of them boot.

The "D" should be a double action one.
The "F" a superfloppy one.



Wonko

Hi Wonko, finally got some time to try these two images. Unfortunately, same results for both. They both start with the "Starting PC DOS" message. But nothing happens after that.

Do you think a strategy where we start with a floppy image that works, the 1.44 MB image, and start tweaking that geometry until it looks like 64MB...or is FAT12 too restrictive for this? thanks.

I am starting to think that PC-DOS checks the actual Drive type (Media Type Byte) in the bootsector.

Both the files you have at offset 21 Dec/15 Hex the value 248/F8 which means "hard disk".

Known values are the following:
F0=Floppy disk
F8=Hard disk
FF=(FreeDos only) autodetect

I've tried all of them, but without success.

It is possible that in PC DOS, F0= means ONLY floppy, i.e. 1,44 or 2,88 and F8 means ONLY hard disk (but the stoopid BIOS maps it as floppy).

So, we are in a catch22.

Time to start a new approach.

What is the reason you need the stick booting to PC-DOS?

What if you actually boot from a PC DOS floppy image?

I'll do some experiments and post a new image to try.

FAT 12 is up to 16 MB, FAT 16 (small sectors - actually identical to FAT12) is up to 32 Mb, from then on we have "BIG sectors".

Wonko

ERRATA CORRIGE 31/07/2011:
The 255 applies to "Disk Number" and NOT to "Media Type"
More details here:
http://www.msfn.org/...on/page__st__84

I don't know that I have a real good reason any more for pursuing this, but you know how things go sometime, you find a challenge and you just want to see it to through.

Part of the reason I think, is that I have this affinity to all things IBM, thus the IBM key, IBM PC DOS etc. I still have an original IBM PC with single 160 KB floppy drive with monochrome monitor. My first career job was with IBM in 1981, the year of the IBM PC and DOS 1.0. I started at the IBM Lab just weeks before the announcement. I lived through and was part of the whole PC revolution from IBM's perspective. I used to know some of the folks that put the whole thing together, both from a technical and marketing perspective.

In any case, a few years ago I built this state-of-the-art PC with all name brand components, Intel motherboard, P4 HT 3.2 Ghz, highest-end Seagate SATA drives in Raid configuration, etc. etc, etc. Its been a workhorse for me and brought me many returns....I've certainly got my share of other store bought machines, but I like to push this machine to its limits and ask it to do anything I want to imagine....EXCEPT this annoying booting problem for IBM PC-DOS from my IBM USB key. I have some DOS programs from a project I developed for PC-DOS that never saw the light of day. I wanted to see if they would run on my machine and be able to demo when some of my IBM friends that worked on the same project come to visit. These are more than 20 year old programs.

I have booted IBM DOS from a real floppy attached to this machine with no problem and I've booted a 1.44MB image from the USB key, no problem.

If you don't think this is worth pursuing, I fully understand and we can both move on from here, but if you have some ideas, I would love to hear them.

I have looked at the media-descriptor byte and I am confused about it. I think what you are saying is that the BIOS over rights this on-boot and totally confuses DOS as to what its booting from? Interesting thought.

Thanks again for your persistence. take care.

Well, I don't know you, but I have no intention whatsoever to let this slip by, though we are at a still right now it doesn't mean we cannot find a solution.

The "Media Type" is ignored by most BIOS/OS, but it is possible that the IBM DOS (or the BIOS) is a "strict" one.

An example (reversed) is the Qemu BIOS, you won't be able to boot a "super-floppy" image mapped as fd0 in Qemu, as it "understands" 1,44 floppies and not volumes.

Give me a few days, I want to try a few of the other tricks first, but how you booted the 1.44 floppy image from the stick?

I mean by "dumbing it down" to overall 1,44 Mb capacity or by using grub4dos or syslinux/memdisk?



Wonko

Hey, I'm all for taking this all the way! thanks for your support.

Here is an image that I can zap the usb stick with using HP Utility and it boots just fine as a floppy A: drive. Of course, it won't boot on any other machines that expect to see a USB HD and not a 'imitation' floppy.

As you'll see it is formatted as FAT12. At first I thought this is the only FAT format my BIOS understands, but then MS-DOS with FAT16 comes up as A: drive and so does FreeDos. So, A: drive can be FAT12 or FAT16,

It appears that somewhere in the IBM DOS boot sequence, there is a check for 'size of drive' and 'drive letter'.
If 'drive letter' is 'A:',
then size must be 1.44
If 'drive letter is C:'
then 'size of drive' can be anything (up to FAT16 or FAT32 limit).

I'll try grub4dos next, haven't played with that one yet.


P.S. I'm having trouble uploading the DOS 7 floppy image... I'm getting 'Upload failed. You are not permitted to upload this type of file' ...some kind of filtering going on? Can I send privately?

P.S. I'm having trouble uploading the DOS 7 floppy image... I'm getting 'Upload failed. You are not permitted to upload this type of file' ...some kind of filtering going on? Can I send privately?

zip or 7zip the file.

Well, I tried uploading a 1.3M file and it will not allow me! Max.single upload size: 990.64K. anything else I can do? I try the Manage current attachments, but it says I have (0).

Use a file hosting and post the link.
Board is having some problems with uploads, but anyway if you have a 1 Mb allowanceyou won't be able to upload a 1.3 Mb file.
But a compressed Dos Floppy image rarely can be larger than, say, 500 Kb, so I am wondering what you are trying to upload.
The "good" news are that if your theory is right (which is possible) being IBM a floppy can surely be 1,44 and 2,88 Mb (you'll have to try it) which can be read either as a 100% increase of available space on device or as a stoopid improvement, being the actual stick 64 Mb.



Wonko

Hi,
Just saw this thread. To boot to DOS always as A:, use RMPrepUSB and format as USB-HDD (pref 2GB or larger) and MS-DOS and FAT16 or FAT32.
Then copy over DOS files. The click on Install Grub button.

Then make a menu.lst as follows

(assumes you have only one hard disk in the system)


# set timeout before automatic boot
timeout 3
# use first menu item by default for boot on timeout
default 0
# if error in default menu, use menu 1
fallback 1


# If the BIOS is set to boot the UFD as a floppy
# this will immediately boot
# If the BIOS is set to boot the UFD as a hard disk
# You will see the menu for the timeout period before it boots

color light-gray/blue black/light-gray

title FDD Boot (from Hard disk UFD)
map (hd0,0)+1 (fd0)
map (hd0) (hd32)
map (hd1) (hd0)
map --hook
chainloader (fd0)/io.sys
rootnoverify (fd0)
map --floppies=1
map --harddrives=1


title FDD Boot (from Floppy UFD)
root (fd0)
chainloader /io.sys

Hi,
Just saw this thread. To boot to DOS always as A:, use RMPrepUSB and format as USB-HDD (pref 2GB or larger) and MS-DOS and FAT16 or FAT32.
Then copy over DOS files. ...
....
chainloader /io.sys

@steve6375
You should actually READ the thread , this is about booting IBM PC-DOS, NOT MS-DOS:
http://en.wikipedia.org/wiki/PC_DOS


PC-DOS has NOT IO.SYS as system file, as well as it has NOT MSDOS.SYS, the corresponding files are:

• IBMBIO.SYS
• IBMDOS .SYS

BTW, and just for the record, last time I checked, grub4dos could only directly chainload the 7.x or (maybe) 8.0 version of DOS' IO.SYS, and not earlier versions:
http://www.boot-land...;showtopic=8102


Wonko