Originally Web posted Wednesday, 21 January 2009.
Content last modified Saturday, 9 January 2021 .
External links last verified Wednesday, 21 January 2009.

Making a 400k MFS Boot Floppy on Any Beige Mac

In the process of helping out a fellow Macintosh hobbyist make a startup disk for his original 512k Fat Mac, to my surprise i learned, or was reminded, that Disk Copy can make 400k MFS format boot floppy disks from a valid bootable 400k MFS disk image… even on OS 8 or 9! This may be of interest to owners of original 128k and 512k Macs with the original 64k ROMs.


As discussed in my Working with Macintosh Floppy Disks in the New Millennium article, Apple dropped OS support for MFS disks as of OS 8.0. Even before that, they dropped direct OS support for formatting floppy disks as 400k MFS. Common wisdom (at least in my head) was that an older Mac with OS support for 400k disk formatting was needed.

Recent testing shows that Disk Copy 6.3.3 can and will format and write a 400k MFS boot disk image onto a single-sided (400k) or double-sided (800k) floppy… even running under OS 9.1 on a 9600/350 PPC Mac! Does not matter if the floppy disk enters the drive formatted (800k or 400k) or blank!


To get this to work, you will need:

This should work all the way through the Beige G3 models running OS 9.2.2, and all the way back to the earliest Mac which can run Disk Copy (at least as far back as the Plus/512ke).

Exact steps known to work (tested on a 9600/350 running OS 9.1 or 7.6.1 with Disk Copy 6.3.3):
  1. Launch Disk Copy.
  2. Select Make A Floppy from the Utilities menu.
  3. Navigate to, and select, the disk image file.
  4. When prompted, insert the floppy disk.

Disk Copy will work away and eventually pop out a 400k MFS format bootable floppy disk! You will not be able to mount that floppy nor the disk image source file onto any Mac OS newer than 7.6.1, yet the disk is a valid MFS boot disk and should boot older Macs.

Not having access to an actual 64k ROM 128k or 512k Mac, the best i could do for testing was have the resulting floppy boot my Mac Plus, and verify that the format was absolutely for sure MFS. I did these tests, with about 4 disk images and about 6 floppies: all worked great and were truly MFS formatted.