Writing 5¼” CP/M floppy disks on a 1.2MB PC drive with Windows 98

Computers are lonely objects without software. I have used the MS-DOS programs Imagedisk (IMD) and 22DISK to write CP/M disks from Internet-sourced disk images for my own Kaypro. Having an MS-DOS computer with a 360k drive means this a straightforward task.

Less straightforward is to use a modern Pentium 4 running WIN98 with a 1.2MB high density drive. Philip Avery has done this for his own Kaypro, and he details the process below...


With the arrival of my Kaypro II (my first CP/M machine - ever), I was keen to download some software for it from the net and write this out to 5¼” floppy disks. I was familiar with this type of operation as I have been doing this to generate disks for my TRS-80 Model III.

Win98 with Kaypro

Photo 1.The computer on the right was needed to get resources for the computer on the left

My set-up is a Pentium 4 (3.2GHz) that has two partitions – XP & Win 98SE. It also has a 5 ¼” 1.2MB floppy drive fitted. This is the only PC I have - I don’t have a bunch of old DOS boxes around with 360KB drives fitted (which would make things easier) - so I was keen to make my set-up work.

There are two programs I came across on the net to write CP/M floppies and the Kaypro II System Disks – 22DISK and IMD. I knew if they were going to work at all on my system – it would have to be under my Win 98SE partition, as XP (including its DOS command prompt) won’t allow those 2 programs sufficient control of the floppy drive to write Double Density. That was why I had a Win 98SE partition in the first instance – so my TRS-80 emulator (under Win 98SE) could write real disks.

IMD worked fine under Win 98SE and could write real floppies that the Kaypro II could read. However 22DISK couldn’t, and declared a hardware error when trying to format a disk. I then opted to have my Win 98SE partition boot to DOS only, as this would be faster when I power down XP and start up DOS. I did this by editing MSDOS.SYS in my Win 98SE partition. First, you have to make MSDOS.SYS visible, from a DOS command prompt (even XP, just make sure you select the correct partition first), do:


Then edit MSDOS.SYS and change BootGUI=1 to 0. (I used Notepad to do this)

This will boot only to DOS – making for a very fast boot for this partition. Plus, 22DISK now worked – excellent.

A further tip: when writing new floppies with IMD (to generate original Kaypro bundled software for example), I found it easiest to Format the floppy under 22DISK first, as it knows the correct settings for a Kaypro floppy, then use IMD to write to the formatted floppy. Doing this meant the only setting I had to set on IMD is the Double Step (as I have a 1.2MB (80 track) drive, not a 360KB (40 track) drive.

I have found the 80 track (double stepped) floppies work fine, provided: the floppy is initially bulk erased (I just pass a strong magnet over it a few times), you then do NOT write to it in a 40 track drive. I use the 80 track disk just as a transfer to the Kaypro. Once it is in the Kaypro, I then copy the disk, thereby creating a proper 40 track floppy.

Philip Avery
February 2010

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