Flux Is Your Friend For Archiving Old Floppy Disks

A beige computer with a CRT monitor. A black LCD sits atop a stack of 3 devices next to it and a set of power control switches (the orange light up kind). There appear to be 8 floppy drives available.

Nothing screams retrocomputing quite like floppy drives. If you want to preserve some of your favorite computing memories like that paper you wrote about the joys of the Information Superhighway, [Shelby] from Tech Tangents has a detailed dive into how to preserve the bits off those old floppies.

Back in the day, the best way to get data off an old drive was to fire up an old computer. Now, with new devices specifically designed for harvesting data off of old floppies like the KryoFlux and the Greaseweazle, you can get the full flux map of the disk. With this, you can build binary image files and actually pull files and duplicate disks from vintage systems.

Some systems, like PCs, Macs, and Commodores are well-understood and are simple to preserve, while others take quite a bit of work to figure out. [Shelby] walks us through some of the more common disk formats as well as some real oddballs like Microsoft Adventure which features inconsistent formatting as a form of early DRM (boo).

Want to do your own preservation? We’ve covered a couple different methods in the past.

13 thoughts on “Flux Is Your Friend For Archiving Old Floppy Disks

  1. The concept reminds me of recording WAV files of datasettes (computer cassettes) by using a soundcard and an ordinary cassette recorder.
    By doing so, someone can save a whole side of a datasette and do the decoding later on.

    The downside is, though, that sometimes the original datasette deck had good physical filtering circuits (low-pass, Schmitt trigger etc) not found in a basic software decoder.

    So a clean, but less faithful digital copy is being traded for a more faithful but hard to decode digitized copy.

    That’s also why certain users tried to attach the original datasette deck of a certain computer system to a parallel port interface, to get a solid digital readout.

    Personally, I thus think it might be worth reading rare or important media in both ways, if needed.

    Using common sense shouldn’t hurt, either.
    For certain things, like a driver diskette or an OEM version of an well-known OS, a sector based copy might still be sufficient.

    1. I really wish they hadn’t described the original one as reading the flux off the disk, because it doesn’t. It reads the logic level output of the amplifiers and signal conditioning stages.

      You can read the actual flux by attaching an oscilloscope or fast ADC to the read head. That can allow recovery of damaged disks where the magnetic field is distorted, or even has been partially overwritten.

  2. I was careless with a floppy. I left it to get beaten up in one of those ‘random moving stuff’ boxes in one of my many college-days moves nearly 30 years ago now. I held on to it though, just in case I one day would have a means to read it.

    Not long ago I finally got around to trying it with a GreaseWeazle.

    Read it on the first try!!!! Like nothing was wrong!

    I definitely recommend this if you have an old floppy to read.

  3. I’m going into beta test with my apple ii disk imager. It still depends on the drive hardware for reading the Flux. I have also designed an analog version that oversamples the small voltages from the read head, amplifies them, and the uses DSP to recover the data.

  4. Probably a silly question, but how can you tell if a 5 1/4″ floppy disk drive is 40 or 80 track ? I vaguely remember having 113 or maybe 140 KiB floppies for an Apple ][e and maybe 160 KIB floppies on a BBC model B. Would they both be 40 track and single sided ? I remember that 5 1/4 for the first 4.77 MHz PC I used was 360 KiB, so I am guessing that was either 80 track single sided or 40 track double sided. Am I right or wrong ?

    1. I’m just a layman, but I think among other things, floppy type detection is possible via drive seek.

      Trying out a different step rate and RPM (300 vs 600) are also possibilities.

      Then, some 80 track floppy drives can “double step” to read 40 track media.

      Again, a layman here. I wished I could answer your original question properly.

      Maybe someone else can do it?

    2. The Apple 5.25″ floppy drives were 35 track, as were other early drives. Their were some 40 track drives for the apple, like the fourth dimension drive. The IBM pc had 40 track double sided drives. There were also some 80 track 720k drives in addition to the 1.2mb floppies.

  5. Oh god, the Apple II was the worst for that sort of early DRM crap because if you wanted to you could bitbang the steppers and thus, by half-stepping, read and write sectors at fractional track offsets so more than a few programs had heavily obfuscates sequences of code to do just that and some would even put deliberately bad sector checksums there so even scanning for good sectors at all fractionsl track offsets didn’t always do the trick so if you wanted to back such a disk up you were left with the bleak choice of reverse engineering where it put everything, remapping that to sane locations, and patching the binaries to look for them there, or, a crapload of trial and error to figure out which fractional offsets mattered to nibble-copy when none of them looked “good”.

    It was an education…

  6. I have tons of Apple too floppies that would love to recover sadly the oxide layer on a lot of these old discs wears off under the pressure of R/w heads leaving you to have clean the heads each session maybe there’s a way to read it without running the heads on top of the disc

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