Accessing Mac Formatted Floppy Disks without a Kryoflux

A Mac HD 3.5" floppy disk: Not compatible with 400/800KB disk drives.

A Mac HD 3.5″ floppy disk: Not compatible with 400/800KB disk drives.

One of the more common questions asked on the various digital curation forums is how to access HFS formatted 3.5” floppy disks. Variations on this question include: “why can’t my USB 3.5” floppy disk drive read old Mac disks?” or, “How do I access double sided double density (DS/DD) Mac disks?” or, “I have a stack of 3.5” floppy disks that neither Windows nor Linux will recognize, what gives?” However the question is formed, a common recommendation from the community is to use a Kryoflux controller card to capture the data from the drive. I’m a fan of the Kryoflux and recommend it regularly, but it does have several limitations, especially when it comes to cost, so I’ve been looking for alternative ways to access HFS formatted disks. While these disks are otherwise uncommon, because Macs were frequently associated with the works of “creatives,” they have an outsized importance in the world of digital archives, and thus merit some special attention. (Quick note: though 5.25″ floppy disks were used by the Apple II, “Macs” only ever used the 3.5″ diskettes, so if I say “Mac floppy disk,” I mean a 3.5″ diskette.) What follows are some recommendations based on my findings. In a way this is a followup to my article a few years ago on building a digital curation workstation and the blog post I wrote for MITH last year on using BitCurator to capture and access data on server hardware. 

Some Background on Mac Floppy Disks

First let me explain the nature of the problem. One of the primary challenges of capturing data from floppy disks (either 5.25″ or 3.5″) is that the same form-factor was used across multiple generations of disk sizes and file systems. The Wikipedia entry on floppy disk formats is a great resource (bookmark it!), but even as exhaustive as it is, it’s still incomplete and doesn’t list all of the various computers and file systems that used the 3.5″ floppy disk. This presents a challenge because the same 3.5″ hard plastic diskette could have been used by a computer from 1985 or 1995, and in most cases with no indication about whether it’s from a Mac, IBM PC, Amiga, or other.

Apple alone used the 3.5″ floppy diskette for disks of three sizes: 400 KB (single sided, double density, or SS/DD), 800 KB (double sided, double density, or DS/DD), and 1.44 MB (double sided, high density, or DS/HD, or more commonly, just HD). What’s more, the 400 KB disks could have been formatted with either the short-lived Macintosh File System (MFS) or the more common Hierarchical File System (HFS). All 800 KB and 1.44 MB would be formatted with HFS. (The HFS+ file system originated with Mac OS 8.1, but because Apple moved away from floppy disks around that time, it is unlikely that you’ll see HFS+ formatted floppy disks.)  I break all this down in the table below.

Disk Type Capacity File System

Variable-Speed vs Fixed-Speed Floppy Drives, or, Why Your USB Floppy Disk Drive Can’t Read a DS/DD Mac Floppy Disk

As I detail in my digital curation workstation post, a USB 3.5″ floppy disk drive will read both IBM formatted (Microsoft FAT12 file system) 720 KB and 1.44MB diskettes, but only 1.44 MB if they are Mac formatted  (HFS). There’s a reason for this other than a general bias against Macs. Until the 1.44 MB floppy disks came out, Apple used a technology called a variable-speed spindle in their floppy drives, where as IBM-compatible systems used a fixed-speed drive. With this technology, Apple was able to eke out more space on SS/DD and DS/DD disks compared to their IBM counterparts, 400 KB to 360KB and 800 KB to 720 KB respectively. In the 1980s an extra 40k or 80k was nothing to be scoffed at, and Apple’s variable-speed drive was clearly the superior technology. But by the time the 1.44 MB floppies arrived, Apple was tired of being the odd-man-out, and adopted a fixed-speed spindle for its HD disks. Thus a present-day USB 3.5″ floppy disk drive is unable to read 400 KB (SS/DD) and 800 KB (DS/DD) Mac floppy disks because it uses a fixed-speed spindle and is unable to read floppy disks created with a variable-speed drive. This is also the reason that Windows software tools such as Omniflop are unable to read 400/800 KB Mac floppy disks.

Moving to a fixed-speed floppy drive meant backward compatibility issues for Apple, as the image at the top of this post suggests. To address this issue, Apple began shipping its computers with what they called the “SuperDrive” (not to be confused with the 120 MB “SuperDisk” that came out in 1997), first with the Apple IIe and later with the Macintosh II.  The SuperDrive had the capacity to read both variable and fixed-speed formatted disks, as well as IBM formatted disks on a Mac. (Just to make things nice and confusing, once 3.5″ floppy drives were retired, Apple repurposed the “SuperDrive” name for its CD-ROM drives, urg.)

There’s one more wrinkle to this history that might get in the way of the digital archivist. As the 1.44 MB floppy disk became the industry standard, there was little or no reason to support 400KB disks going forward, so in 1997, with the release of OS 8, Apple dropped support for MFS. The upshot being that if you happen to have 400KB Mac floppy disks formatted with MFS, then you need a system running Mac OS 7.6.1 or older to read them. And while MFS formatted disks may be rare, any and all Mac disks from 1984 to 1986 would be MFS formatted because it was the only option availabe.

Mac 400/800KB Access Methods

As stated above, the most common recommendation for accessing data on legacy Mac floppy disks is using the Kryoflux, which works. However, I see two main problems with using the Kryoflux. The first is cost. For institutional use the costs for a Kryoflux and software license are (at last check) around $2,500. Not insurmountable, but not chicken feed either, and beyond the means of many smaller collecting institutions. The second issue I have with the Kryoflux is that it requires three steps to actually view the contents of a disk. First you capture a stream of the magnetic fluxes, second you encode the stream into the appropriate format for the disk type and create a disk image, and then finally you mount the disk image on either a working Mac or through an emulator. This multi-step process is fine if you know that you want the contents of the disk, but if you’re still just appraising the disks and aren’t sure the content is of value, that’s a lot of extra work.

An alternative to the Kryoflux approach is to purchase or find an older Mac system with a 3.5″ floppy SuperDrive, which at the time of this post can be had for $100 – $200 on eBay or Craigslist. This is not a new idea, obviously, but the trick is knowing which legacy Mac systems would make the most useful inclusion in the digital archivist’s toolbox. These access systems, what Doug Reside calls “Rosetta Computers” (see page 20 in the PDF linked here), need the capacity to both read legacy floppy disks and transfer that data to a newer system vie network or other means. In the link above, Doug recommends the Macintosh PowerBook G3 “Wallstreet” edition because that particular laptop was the last Mac to ship with the 3.5″ floppy SuperDrive. After that, Mac systems shipped with regular 3.5″ floppy drives, including the two PowerBook G3 editions that followed the “Wallstreet” edition (named “Lombard” and Prismo”, and noted for their bronze looking keyboard).  This is a solid choice, and one used by MITH on a number of digital preservation projects. However, the PowerBook G3, regardless of edition, shipped with Mac OS 8.1, which meant that it cannot read MFS formatted 400KB disks. For that you will need a Mac running System 7.6.1 or older.

Recommended Macintosh Access Systems

So which Macintosh systems should the digital archivist add to their toolbox in order to access/appraise a complete range of legacy Mac floppy disks? There are a number of possibilities, but primarily the access system should meet the following three criteria:

  1. The system includes a SuperDrive 3.5″ floppy drive
  2. The system can run Mac OS 7.6.1 or older
  3. The system includes the means to easily transfer data to a modern computer (ideally via network)

Number three above is a somewhat optional because in a sense every system with a SuperDrive includes its own transfer method: simply create a disk image of the SD or DD disk and then copy it to a 1.44MB HD disk which can then be read by a USB floppy disk drive. This “sneakernet” method, however, gets us back to a troublesome multi-step process, so I recommend looking for a legacy system that either includes an Ethernet jack or, for desktops, has the capacity to add on a USB expansion card.

Below, then, I offer some recommendations. I am indebted to Sonic Purity and his article “Working with Macintosh Floppy Disks in the New Millennium” for many of these recommendations, and also much of the technical details above. For those interested in a more in-depth description of Mac floppy disks and their history, I highly recommend it.

Laptop Recommendations

Mac PowerBook 1400c or  3400c

This series of PowerBooks are the immediate predecessors of the G3 models discussed above. While I would usually recommend the PowerBook G3 “Wallstreet” edition, all PowerBook G3 laptops shipped with Mac OS 8.1, and thus won’t read MFS formatted disks. The PowerBook 1400c and 3400c offer performance close to that of the G3, but with MFS support.  If you can find one of these laptops in working order, this is perhaps your best option because they are a self-contained computer–no need to buy keyboard, monitor and mouse separately. A few things to keep in mind if you go with a PowerBook:

  • The 1400c and 3400c have swappable drive bays that can hold a floppy drive, Zip drive or a CD-ROM drive. Make sure the system you buy includes the floppy drive at the very least, but opt for the Zip drive as well if you can find one because…
  • Only the 3400c has Ethernet capacity built in. You can add Ethernet support to the 1400c through a PC card (aka, PCMCIA card), but the chances of finding one that has drivers for the 1400c are slim. For this reason, I strongly recommend the 3400c if you can find one.
mac laptops

Image credit Wikipedia

Desktop Recommendations

Power Macintosh 7200 – 7600 / 8200 – 8600 / 9200 – 9600


Power Macintosh 7200; Image credit Wikipedia

These computers were built and sold from 1995 to 1998 and were the first generation “Power Macintosh” systems before Apple added the G3 (and subsequently G4 and G5) naming convention.  Each of these Power Macintosh systems can run Mac OS 7.6.1, include a SuperDrive floppy disk drive, and come standard with a 10base-T Ethernet network jack–everything you need to access the full range of legacy Mac floppy disks and transfer the images to a modern computer. (The 7100 and 8100 models are not recommended because they don’t include an Ethernet jack.)

Thus, the full list of potential “Rosetta” systems for reading Mac floppies would be:

Acquiring you Legacy Mac Access System

The easiest option for acquiring one of these systems is, of course, eBay. At the time of this writing there were about a dozen of the above systems (desktops and laptops) for sale on eBay, with prices ranging from $50 to $250. Craigslist and computer recyclers are also options. However you acquire the system, be prepared to do a little work on it–installing Mac OS 7 at the very least. Common issues you might expect are a missing power cord or a missing hard drive. Keep in mind that there is a finite number of these legacy systems out there, and at some point in the not-too-distant-future, they’ll be gone. Acting now to build this access capacity in your digital curation toolbox will make you look very smart the next time someone hands you a box of legacy media and asks you to figure out just what the heck they’ve acquired.

The Kryofux is a powerful tool, and given the means, the digital archivist should have one at her disposal. However, even discounting the expense, they are still an imperfect access tool because they require so many steps to view the disk’s contents. For $100 to $250 and a little TLC, a library, museum or archive can expand its capacity to read the full-range of Mac floppy disks and conduct appraisal and analysis of the content quickly and easily.




One thought on “Accessing Mac Formatted Floppy Disks without a Kryoflux

  1. This is great! Your blog posts on tech I’m unfamiliar with are always really clear to me. I like that you address needs of smaller collecting institutions/underfunded units & common issues to watch for with eBay’d computers, too.

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