Solving Floppy Disk Problems

Dan Knight - April 1998, updated Dec. 2001

I can't read this floppy in one Mac, but it works just fine in my other Mac.

There are several possible culprits, the most likely being the disk format. The earliest Macs used single-sided 400k floppies, which some of the Power Macs cannot read. In 1986 Apple introduced double-sided 800k floppies on the Plus. Previous Macs will not work properly with double-sided disks.

A few years later Apple started shipping high-density floppies (called FDHD or SuperDrives). These 1.4 MB disks cannot be read in any Mac without a high-density drive. If you're trying to read 1.4 MB disk in a Plus, unupgraded Mac II, or early SE, that could be the problem.

Another possibility is that you've managed to format a high-density (HD) floppy in an 800k drive. I've seen this fairly ofter. Macs recognize HD disks by the second square cutout on the disk. Since pre-HD Macs don't look for that, they are perfectly content to format these disks to 800k. To make these disks readable in a newer Mac, put opaque tape or a label over the HD square.

Still another possibility is that you are using IBM formatted disks. Macs with HD drives can read and write IBM floppies, but only if PC Exchange, DOS Mounter, or a similar program is installed. But that's only in Macs with HD floppies - you can't use IBM format disks in 800k drives.

With modern Mac lacking an internal floppy drive, reading Mac and PC high density drives isn't a problem, so long as you have a USB floppy drive. However, none of the USB floppy drives will read Mac 800k floppies.

Finally, there's the possibility that one of your drives is out of alignment or needs to have its heads cleaned. Cleaning is usually simple: insert a cleaning disk. And sometimes blow out the dust bunnies with compressed air - it's amazing how much dust can accumulate inside a floppy drive.

The older a drive and the more heavily used, the more likely misalignment. The only solution is to replace the drive, which is typically about $60 and usually an easy installation. (Big exception: compact Macs such as the Plus, SE, and Classic.)

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