View Full Version : PS/2 Model 25-001 Floppy Woes

March 24th, 2006, 05:46 PM
I just aquired an IBM PS/2 Model 25-001. It uses a 720k DD floppy drive. I need to create some DOS and the BIOS startup disks, but I have no modern computers which have a 720k floppy drive. I tried using another PS/2 1.44MB drive, but I still can't boot from it. All I get is IBM BASIC. Any suggestions?

March 24th, 2006, 06:37 PM
A modern 1.44MB drive uses high density media. An older 720K drive uses double density media. The good news is that the 1.44MB drives will correctly read and write on double density media.

So you have two tasks:

- Find genuine double density diskettes. These will be labeled as 720K or 1MB capacity disks. Contrast these to high density disks, which are usually labeled as 1.44MB or 2.0M in capacity. You need to get the double density disks; using high density disks is not reliable because of the differences in the media.

- Get an image of DOS in 720K format. DOS 3.3 is one example of a DOS version that was shipped in this format.

Once you've done these two things you can use your modern PC to write the image to the 720K disk.

For reference, take a look at the following web page:



March 24th, 2006, 07:07 PM
I've tried. I do have genuine DD disks. When I try to access them on XP with my BIOS set to 1.44, Windows can't format the disk. When I change the BIOS setting to 720k, Windows sees it as a 5.25" and can't format the disk.

March 24th, 2006, 11:14 PM
All right, I got it to boot to the startup disk, but any MS-DOS disks don't work

March 25th, 2006, 05:56 AM
First, leave the BIOS settings on the XP machine alone. Those are 1.44MB drives and should be treated as such.

You can format the 720K diskettes in a 1.44MB drive. The trick is to use the right format command. Instead of just using 'format a:' you need to use 'format a: /f:720' to tell it to lay down a 720K format. Windows 98 and Windows 2000 will do this - I'm not sure if XP will.

What do you mean that it will boot but the disks don't work?

March 25th, 2006, 09:25 AM
I was able to get my machine to format a 720k disk with that switch. And I was able to boot the machine to the "startup" disk (reference disk type thing), But anytime I make a disk with the MSDOS startup files, the computer will not boot. It just sits at a blinking cursor. I have the image files for many MSDOS boot disks, but the program I have will not write the images to 720k floppies. It says that the data and media do not match.

March 25th, 2006, 10:13 AM
What are the file sizes of the images, and what format are they in? You're not trying to shove 1.44mb images onto 720k disks, right?

The best image format is a raw sector dump. Most disk imagers support that. The nice thing about a raw sector dump is that it's easy to tell what the source diskette was - just look at the file size. The images can also be mounted and examined by Linux without ever touching physical media.

March 25th, 2006, 10:21 AM
the images consist of both IMZ and IMG files.The IMZs are self extracting, but that extraction program will not see the 720k floppy. I've tried boot images for MSDOS 3.3, 4.0, and 6.21. No avail. They all want 1.44MB disks

March 25th, 2006, 11:14 AM
The trick is to get a boot image that is designed for a 720K diskette. DOS 3.3 shipped on both 5.25 and 3.3, and should be available as a 720K image. The second trick is to get a program that can handle raw, unadulterated images. The 'dskimage' program on the web page I referred to earlier can do that.

Check your private messages ..

March 25th, 2006, 06:14 PM
I have finally gotten this thing to boot, using a FreeDOS boot diskette. Now, I have been trying to install a second drive so I can do something other than DOS diagnostics. I have a few 1.44MB drives from an IBM PS/2 system. Could I use one of these as a second drive, or does anyone have a hard drive compatible with this model?

March 25th, 2006, 09:11 PM
all right. Apparently even though I installed a 1.44MB drive, it still can only read 720k disks. Must be a motherboard thing. But I'm playing tetris on it!

March 26th, 2006, 01:52 PM
It has a double density controller .. just like the PC, XT, and PCjr. The best you are going to get is 720KB even if you use a new 1.44MB drive.

I'm still puzzled about the diskette images I sent you .. genuine DOS 3.3 should have run on that machine just fine.

March 26th, 2006, 02:10 PM
Well, FreeDOS is okay for now. Eventually, I hope to get a real version on here. I also wish the B drive would work consistantly, but its good enough for now

April 10th, 2009, 04:52 AM
The model 25 was only a 720K drive and if I remember 7 databits so specific to IBM.
With the boot disk you are trying to copy - are you using the select command rather than the straight forward copy command?

April 10th, 2009, 09:31 AM
>...does anyone have a hard drive compatible with this model?

am i correct in thinking that the model 25 has an isa slot available? and that the 8bit ide adapter (see: http://www.vintage-computer.com/vcforum/showthread.php?t=12359) discussed in another vc thread might be used to add a hard drive to the model 25?

April 10th, 2009, 09:44 AM
FYI, this thread is 3 years old. The OP hasn't logged on in about 3 months.

April 10th, 2009, 10:39 AM
Yes "one day" we will figure out some way to make OLD THREADS more noticable. I have been tricked by this multiple times already. My recent one where the guy was offering hundreds of items comes to mind.

April 10th, 2009, 01:35 PM
hmmm... i feel a little.. foolish. next time i will look at the date before jumping in.

Terry Yager
April 11th, 2009, 12:18 AM
Yes, jj, IIRC the Model 25 should have two slots on a riser. As for if anything will work in 'em, wellllllll...it is a PS/2 (sorta)...