Undiskcopy: Turn Disk Copy 4.2 images into something you can use

A great deal of early Macintosh software was archived in Apple Disk Copy 4.2 format (archive.org link for when 68kmla is down). Undiskcopy converts those images into raw disk images that can be written directly to media, e.g. to a floppy disk using dd.

Building

Just run make.

Usage

$ undiskcopy input-file.img output-file.img
$ dd if=output-file.img of=/path/to/floppy/device bs=512 conv=noerror,sync

Warning: the name of the device file that represents a USB floppy drive on OS X (and likely other systems) can change. Make sure that the path you use in the dd command's of= argument actually refers to the floppy drive and not to something you wanted to keep!

Compatibility

Undiskcopy should build and run on any somewhat POSIX-ish system that has a C99 compiler. It probably won't compile out of the box on Windows systems, but porting should be trivial.

If the file command describes an image file as "Apple DiskCopy 4.2 image", this tool should be able to convert it.

Tags are ignored if present. That's almost certainly not a problem for Macintosh disks, but some sources indicate that tags could be essential on the Lisa. I don't have a Lisa so I don't know whether Lisa images converted by undiskcopy will work. See discussion in the format specification linked above and at https://macgui.com/news/article.php?t=482.

Support, or lack thereof

This software is a home-cooked meal. I made it for me. If you find it useful, that's a happy side effect. I'm making it available with absolutely no warranty whatsoever and no promise of support, bug fixes, or future development of any kind. Use it at your own risk.

You are welcome to report bugs, but I don't promise to fix them. I'm more likely to act on bug reports that contain all the information I need to reproduce the bug. In most cases that includes a copy of the disk image that you were using when you encountered the bug.

License