NerdWorld Report

Greaseweazle Floppy Disk Controller

May 7, 2025

The Greaseweazle is a very versatile tool to read and write dozens (hundreds?) of various floppy disk formats. It's a "Must-Have" tool for retrocomputer enthusiasts because it can read and write to IBM, Tandy, Osbourne, Acorn, and Atari floppies. It helps solve the problem of getting software onto older, non-networked computers. It's only limitation is the lack of support for older Apple computer such as the Apple II and the original Macintoshes.

Retro-computer Dilema Solved

It's a HUGE problem for retro-computer enthusiasts: How to get software on their old machines.
In ancient times (i.e.: pre-networked days), most computers used floppy disks to install software or transfer data from one machine to another. Floppy disks have gotten smaller over the years. They started as 8-inch behemouths, shrunk to 5.25", then evolved a plastic shell and shrunk to 3.5". They stayed there for a long time before gradually dying out. Along the way, capacities increased from a few tens of kilobytes per disk, to multiple megabytes per disk. They're basically worthless now since their capacities are limited and USB thumb drives are MUCH larger and far more reliable. And of course, since networking is ubiquitous, nobody needs them to transfer data or software.

But this presents a problem to the retro-computer enthusiast: How to get old software onto their old computers?

When I aquired an original IBM 5150 PC, I discovered that I couldn't do much with it. I wanted to install a 1980's version of MS-DOS and a suite of software like Lotus 1-2-3 or Ashton-Tate's dBASE III. These programs are now 40-year old abandonware, but are thankfully available through sites such as WinWorld and Archive.org.

So, you can download the disk images, but how to get them onto a real floppy that the retrocomputer can read?

The Greaseweazle is essentially a modern floppy disk controller. It plugs into a standard floppy drive (8-inch, 5.25-inch, or 3.5-inch) and allows a modern computer to read and write floppy disks via a modern USB interface. In addition, it can read and write on the "flux" level, which means it really gets down into the weeds of floppy disk recording. I use it to read and write ancient floppies for my IBM PC and my Osbourne 1 CP/M machines. But super-nerds can also use it to read and manipulate individual bits on an old floppy.

Wither Apple II?

The Greaseweazle understands and speaks a large variety of old floppy disk formats. But there is one glaring ommission: Apple II. Unfortunately, the brilliant and creative Steve Wozniak developed a simple, elegant, and low-cost disk system that has zero compatibility with the standard Shugart drives of the day. Apple eventually went with standard drives, but anything prior to the 1988's Macintosh IIx uses a floppy disk incompatible with the Weazle. Apparently, there is a similar device for old Apple drives, applesauce, but it is much more expensive and rquires an actual Macintosh to drive it. (It may not even be available anymore.)

Using the Greaseweazle

Using a greaseweazel is very simple. You can download the greaseweazle software here. There is no "man" page, but copious help is available by typing:

gw --help

Secondly, you must download the floppy images you want to produce. See WinWorld and Archive.org.

Thirdly, you open your old retro-computer, disconnect the floppy from the computer's controller card and plug it into the Greaseweazle. Turn on the computer, plug in the greaseweazle to your new computer (which has the disk image file) and type:

gw write --format=ibm.360 <imagefile.img>

The format can be any number of pre-defined formats. Typical ones are "ibm.360" for IBM 360K floppies. There's also "IBM.1440" for 3.5-inch 1.44 MByte disks. See the full list at the Greaseweazle Wiki.

Stand-alone Greaseweazle Setup

I didn't want to have to open my IBM case every time I needed a new floppy disk, so I decided to make a stand-alone Greaseweazle setup. I bought an old IBM 360K floppy on eBay. I also bought a "molex power supply" from Jameco. I mounted these on a piece of shelf-board along with the greaseweazle and a power switch.

Now I can read and write IBM and CP/M disks to my heart's content! (But sadly, no Apple II)