Problems with Floppy Disks

Originally published 29 March 2000 as a Mac Daniel column for Low End Mac.

Q: I have a newer PPC Mac (running OS 8.x or 9.x) and an older 68K Mac. I'm having problems with sharing floppies between the two. What gives?

A: Apple has used three types of floppies in Macintosh computers since 1986.

400K: These were the original floppies used with the 128K and 512K. They are supported (at least partially) in the Mac OS up to Mac OS 7.6.1. For a very complete description of the limitations of System 7.x in handling 400K floppies, please see TIL article 9502. 400K floppies are not supported in Mac OS 8 or later; you must copy the data onto an 800K or 1.44 MB disk in order to transfer it to your newer Mac. Interestingly enough, according to the TIL, Mac OS X Server does support 400K (and 800K) floppies, but in read-only mode. (1.44 MB floppies are fully supported.)
800K: The 512e was the first Mac to support 800K floppies internally, while the 512 will support them in an external 800K drive only if you follow the directions in TIL article 1777. All System Software since the 512e was released supports 800K floppies. (This may change in Mac OS X, but we won't know until it's released. Mac OS X Server supports 800K floppies in read-only mode.) All Macintosh computers support 800K floppies as well, unless those computers have USB onboard, in which case there is no Apple-branded floppy drive available for them. They require a third-party floppy drive. Due to differences in (and the higher cost of) the GCR floppy mechanism, the manufacturers making third-party floppy drives chose not to support the 800K disks in USB drives. The very common Imation SuperDisk drives (including the VST PowerBook Expansion Bay version) do not support 800K disks. You won't damage an 800K disk by putting it in the drive, but it won't recognize the disk and won't be able to reformat it. (Note: some of the PowerBook G3 Series machines, a.k.a. PDQ or WallStreet 1.1, with 14.1" screen and 66 MHz bus speeds, did not ship with a floppy drive. There are, however, Apple floppy drives available for these machines, and they work with both 800K and 1.44 MB disks.)
1.44 MB: Without the use of third-party external drives and software, there is no way to get 1.44 MB disks to work with a Mac Plus. The Applied Engineering HD+ floppy drive will not work with anything earlier than a Plus. The SE originally did not support 1.44 MB floppies, but can be upgraded with a SuperDrive and the proper ROM and SWIM chips to do so. The Macintosh II requires a PMMU or a motherboard upgrade to a IIx motherboard in order to use SuperDrives. All Macintoshes after the SE and II, as well as all System Software since at least version 6, support 1.44 MB disks. If your Mac didn't come with a floppy drive, don't worry — the third-party USB drives will work fine with your 1.44 MB floppies.

As long as your floppy is supported on both Macs, you shouldn't, in theory, have any problems using the disk on either system. However, I've found that rebuilding the desktop, especially when going from System 6 to Mac OS 8.x (and vice versa), can be helpful in keeping away those pesky error messages. To rebuild the desktop, hold down command and option while inserting the floppy. A message should come up asking if you want to rebuild the desktop file. Click OK and wait while it rebuilds the desktop.

Another issue you might run into is 1.44 MB disks formatted to 800K in older Macs with 800K floppy drives. These Macs will gladly format floppies in the only format they understand, but Macs that can read 1.44 MB floppies will see these as unformatted or misformatted and offer to format them. If that's your problem, all is not lost. You can put some opaque tape over the high density sensor hole, the small square that doesn't have a sliding write-protect switch. This will let you read and write a 1.44 MB floppy formatted to 800K, but it's not something you should do on a regular basis.

If you still have problems, let it be known that floppies are not known to be the most reliable medium in the world for storing important data. It's quite possible, especially if you haven't used the floppy in a while or it's old (2+ years, especially if 800K) that the magnetic surfaces have started to degrade and the floppy won't work very well, if at all. In this case, copy as much as possible off the floppy and throw it away so you won't be tempted to use it again.