Vintage Macintosh: Floppy Disks

800k FloppyUp until 1998, Macintoshes came with or had available a floppy drive. The first iMac came without a floppy drive (or even one as an official option). If you have a vintage Macintosh, then you will be working with floppy disks, and it is worth revisiting the floppy disk.

A Refresher On Floppy Disks

Macintoshes supported 3.5″ floppies, which weren’t actually all that “floppy” when you looked at them. They started with a few different names (micro diskette, mini disk, minifloppy), but they carried the same name (floppy) as their 8″ and 5.25″ predecessors. The actual media that carried the data was the “floppy” part, and was usually a flexible disk coated with a magnetic media. The 3.5″ featured a reasonably strong and rigid plastic case and a spring-loaded cover to protect the media inside. There were actually 3 different kinds of 3.5″ floppies over the years, with the amount of storage available increasing with each generation. How much data you could put on them was also different between the Macintosh, Amiga and IBM-compatible PCs.

SSDD, DSDD and HD

The first 3.5″ floppies were “Single Sided Double Density” (SSDD), meaning that only one side of the diskette’s media was available. These diskettes held 400k on a Macintosh, but only 320k on a PC (more on why this was later). These were followed by the “Double Sided Double Density” (DSDD) diskette, which doubled the storage to 800k (720k on a PC). Externally, the two diskettes looked identical, and you could format a DSDD as an SSDD if you wanted. In 1989, Apple introduced the Macintosh SE/30, SE FDHD, IIcx, IIci and Macintosh Portable. These featured the first use of the new High Density (HD) 3.5″ floppy, which held 1.44MB. Unlike the first two generations, the Macintosh didn’t put any more data on the diskette than the PC did. At a glance, the two look very similar.

two floppies

But if you look carefully, there is one distinguishing feature: the extra hole on the HD diskette. 1.4M Floppy Annotated

The DSDD diskettes don’t have this hole.

800k Floppy Annotated-01

This allows the drive to detect whether a DSDD or HD diskette has been inserted, and work accordingly.

DSDD vs. HD

If you need to make 400k or 800k diskettes for an older Macintosh, then you need to find DSDD diskettes. They are still around, but are increasingly harder to find. But if the only visible difference between a DSDD and HD diskette is the hole, why can’t you just put tape over the hole on a HD diskette? The problem is that the HD diskettes had other differences that weren’t visible. Sure, the form-factor and external design was virtually the same. But the magnetic material, and how it was laid down, was different from a DSDD diskette (the Wikipedia article has more detail on this). The result is that, if you try to use an HD diskette as a DSDD diskette by covering the hole, you may find it won’t work reliably (I’ve had some experience with this, all negative).

Why Did The Mac Have More?

When compared to the PC, the Macintosh put more data on SSDD and DSDD diskettes (the Amiga put the most on them). How did the Macintosh manage that? By using a variable-speed floppy drive. On PC’s, the floppy drive would spin the diskette at a constant speed. That meant that, as the disk head moved towards the outside, the sectors would be bigger (because more of the media passed over the head as it spun). With a variable speed motor, the Macintosh would slow the rotational speed down as the head moved towards the outer edge, making all the sectors more similar in size. This meant more sectors, which resulted in more data. It did mean, though, that only Macintosh floppy drives could format and use Macintosh floppies. You couldn’t use the floppy drive in a PC to format a DSDD floppy for use on a Macintosh, because the sector sizes were all different.

The Vintage Determines The Floppy

What floppies will work in your vintage Macintosh depend on the age of your machine. When you are buying blank floppies, pay close attention to which you get. If your machine only supports DSDD, then you need to buy blank DSDD disks (which are still available, although in diminishing quantities). Trying the “tape over the hole” trick with an HD floppy just isn’t reliable enough. It also means you have to pay attention to any floppies you get with software or data on them. Getting a version of Microsoft Office on HD floppies won’t do you much good if you have a Macintosh Plus. Make sure that the floppies you get will work with the Macintosh you have.

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