(If you’re reading this on GitHub, the formatting’s a bit messed up. Try the version on cowlark.com instead.


The FluxEngine is a very cheap USB floppy disk interface capable of reading and writing exotic non-PC floppy disk formats. It allows you to use a conventional PC drive to accept Amiga disks, CLV Macintosh disks, bizarre 128-sector CP/M disks, and other weird and bizarre formats. (Although not all of these are supported yet. I could really use samples.)

The hardware consists of a single, commodity part with a floppy drive connector soldered onto it. No ordering custom boards, no fiddly surface mount assembly, and no fuss: nineteen simpler solder joints and you’re done. You can make one for $15 (plus shipping).

Don’t believe me? Watch the demo reel!

Important note. On 2020-04-02 I changed the bytecode format (and firmware). Flux files will need to be upgraded with fluxengine upgradefluxfile. The new format should be more reliable and use way, way less bandwidth. Sorry for the inconvenience.


It’s open source on GitHub!


This page was getting kinda unwieldy so I’ve broken it up. Please consult the following friendly articles:

  • Frequently asked questions ∾ but why…? ∾ does it…? ∾ can it…?

  • How the FluxEngine works ∾ nitty gritty of the sampler/sequencer hardware ∾ useful links on floppy drives ∾ why I’m not using an Arduino/STM32/ESP32/Raspberry Pi

  • Making a FluxEngine ∾ what parts you need ∾ building it ∾ setting up the toolchain ∾ compiling the firmware ∾ programming the board

  • Using a FluxEngine ∾ what to do with your new hardware ∾ flux files and image files ∾ knowing what you’re doing

  • Troubleshooting dubious disks ∾ it’s not an exact science ∾ the sector map ∾ clock detection and the histogram


The current support state is as follows.

Dinosaurs (🦖) have yet to be observed in real life — I’ve written the decoder based on Kryoflux (or other) dumps I’ve found. I don’t (yet) have real, physical disks in my hand to test the capture process.

Unicorns (🦄) are completely real — this means that I’ve read actual, physical disks with these formats and so know they work (or had reports from people who’ve had it work).

Old disk formats

Format Read? Write? Notes
IBM PC compatible 🦄 🦄 and compatibles (like the Atari ST)
Acorn ADFS 🦄 🦖* single- and double- sided
Acorn DFS 🦄 🦖*  
Ampro Little Board 🦖 🦖*  
Apple II DOS 3.3 🦄   doesn’t do logical sector remapping
Amiga 🦄    
Commodore 64 1541 🦖   and probably the other GCR formats
Brother 120kB 🦄    
Brother 240kB 🦄 🦄  
Brother FB-100 🦖   Tandy Model 100, Husky Hunter, knitting machines
Macintosh 800kB 🦖   and probably the 400kB too
TRS-80 🦖 🦖* a minor variation of the IBM scheme

*: these formats are variations of the generic IBM format, and since the IBM writer is completely generic, it should be configurable for these formats… theoretically. I don’t have the hardware to try it.

Even older disk formats

These formats are for particularly old, weird architectures, even by the standards of floppy disks. They’ve largely been implemented from single flux files with no access to physical hardware. Typically the reads were pretty bad and I’ve had to make a number of guesses as to how things work. They do, at least, check the CRC so what data’s there is probably good.

Format Read? Write? Notes
AES Superplus / No Problem 🦖   hard sectors!
Durango F85 🦖   5.25”
DVK MX 🦖   Soviet PDP-11 clone
Victor 9000 🦖   8-inch
Zilog MCZ 🦖   8-inch and hard sectors


  • IBM PC disks are the lowest-common-denominator standard. A number of other systems use this format in disguise (the Atari ST, late-era Apple machines, Acorn). FluxEngine supports both FM and MFM disks, although you have to tell it which one. If you have an unknown disk, try this; you may get something. Then tell me about it.

  • Not many formats support writing yet. That’s because I need actual, physical hardware to test with in order to verify it works, and I only have a limited selection. (Plus a lot of the write code needs work.) There hasn’t been a lot of demand for this yet; if you have a pressing need to write weird disks, please ask. I haven’t implement write support for PC disks because they’re boring and I’m lazy, and also because they vary so much that figuring out how to specify them is hard.

If you have samples of weird disks, and want to send them to me — either FluxEngine, Kryoflux or Catweasel dumps, or (even better) actually physically — I can identify them and add support.

Please note that at this point I am not interested in copy protected disks. It’s not out of principle. It’s just they’ll drive me insane. FluxEngine will most likely be able to read the data fine, unless they’re doing bizarre things like spiral tracks or partially encoded data, but let’s stick with normal conventionally formatted disks for the time being!


That said, I need to post a warning.


Floppy disks are old, unreliable, and frequently damaged and/or filthy. I expect you to know what you’re doing and be responsible for your own actions. It’s entirely possible for a damaged disk, when read, to scrape the magnetic coating off the disk and pack it into the drive’s disk head, not only permanently damaging the drive, but also irrecoverably destroying any data on the disk.

If this happens and you complain to me, I will be sympathetic but fundamentally unhelpful. Proceed at your own risk.

Remember: FluxEngine is not a substitute for a real data recovery service. Is your data worth money to you? If so, don’t try to read it using an open source project hacked together by some person you’ve never met on the internet.

Also, remember to clean your disk heads.

********** END OF WARNING **********


The FluxEngine was designed, built and written by me, David Given. You may contact me at dg@cowlark.com, or visit my website at http://www.cowlark.com. There may or may not be anything interesting there.


Everything here except the contents of the dep directory is © 2019 David Given and is licensed under the MIT open source license. Please see COPYING for the full text. The tl;dr is: you can do what you like with it provided you don’t claim you wrote it.

As an exception, dep/fmt contains a copy of fmt, maintained by Victor Zverovich (vitaut <https://github.com/vitaut>) and Jonathan Müller (foonathan <https://github.com/foonathan>) with contributions from many other people. It is licensed under the terms of the BSD license. Please see the contents of the directory for the full text.

As an exception, dep/emu contains parts of the OpenBSD C library code, Todd Miller and William A. Rowe (and probably others). It is licensed under the terms of the 3-clause BSD license. Please see the contents of the directory for the full text. It’s been lightly modified by me.

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