Q. Why not just use a USB floppy drive? There are lots and they’re cheap.

A. Because USB floppy drives typically support a very limited set of formats — typically only IBM 1440kB and 720kB. The FluxEngine should work on (almost) anything, including the ones that IBM machines won’t touch. Also, as it’s USB, it’ll work happily on machines that were never designed for floppy disks (like my development Chromebook).

Q. But aren’t floppy disks obsolete?

A. Absolutely they are. That doesn’t mean they’ve gone away. Good luck with any old hardware, for example; a classic Mac won’t boot without a classic Mac boot disk, and you can’t make them on PCs (because they’re weird). This is where the FluxEngine comes in.

Q. But how can you read and write non-PC formats on a PC floppy drive?

A. Because the FluxEngine hardware simply streams the raw magnetic flux pulsetrain from the drive to the PC, and then the analysis is done off-line in software. It doesn’t rely on any floppy disk controller to interpret the pulsetrain, so we can be a lot cleverer. In fact, the disk doesn’t even have to be spinning at the same speed.

Q. Does it work on 5.25” drives?

A. Yes! Although PC 5.25” drives spin at 360 RPM rather than 300 RPM, which means there’s only 166ms of data on one per track rather than 200ms; if you try to write a 3.5” format disk onto one it probably won’t work.

Q. Does it work on 8” drives?

A. Probably? You’d need an adapter to let you connect the drive to the FluxEngine — you can get them. I don’t have either the adapter, the drive, or any 8” disks. If anyone wants to give it a try, please tell me about it.

Q. Does it work on hard sectored disks?

A. Probably? I already have decoder support for some hard-sectored disk formats, based on Kryoflux streams people sent me, and the firmware supports reporting index hole information, so in theory it should work; but I haven’t had the chance to try it end-for-end. I really need a hard-sectored 5.25” floppy to test with.

Q. Does it work with flippy disks?

Uhhh… probably not.

So the problem with flippy disks (5.25” single-sided disks which could be inserted upside down to read the second side) is the index hole. Trouble is, the window to let the sensor see the index hole isn’t symmetrical on a 5.25” disk, so if you turn the disk upside down, the drive can’t see the hole any more:

non-flippy 5.25 inch disk

Some flippy disks had two windows, so they’d work properly either way up, but most didn’t. This was fine on a lot of old machines because those drives didn’t have an index hole sensor. But a lot of modern drives use the index hole to detect whether the disk is actually present and if they don’t see it, they simply won’t work. There’s nothing FluxEngine can do; it’s a hardware limitation.

(If you have one of the rare disks with two index holes, then FluxEngine will read those.)

There are workarounds. One is to read the data on the other side of the disk using the other head — because, of course, modern drives are double-sided. Sure, the disk is spinning in the wrong direction, but that’s no problem. Except there is a problem, which is the tracks on the two sides of the disk are not in the same place; one side has them offset eight tracks compared to the other. But a flippy disk has both sets of tracks in the same place, because they’re both accessed using the side 0 head…

The only real way round this is to modify a 5.25” drive. That’s seriously not in FluxEngine’s remit. Sorry.

Q. Is this like KryoFlux / Catweasel / DiskFerret? Do you support KryoFlux stream files?

A. It’s very like all of these; the idea’s old, and lots of people have tried it (you can get away with any sufficiently fast microcontroller and enough RAM). FluxEngine can read from KryoFlux stream files natively, and there’s a tool which will let you convert at least one kind of Catweasel file to FluxEngine’s native flux file format.

Q. Can I use this to make exact copies of disks?

A. No. FluxEngine can read disks, and it can write disks, but it can’t write flux files that it read. There’s several reasons for this, including but not limited to: amplification of disk noise causing unreadable disks; needing to rearrange the read data so it all fits exactly between the index markers; reproduction of non-repeatable noise (this was a common trick with Apple II copy protection); etc. What FluxEngine prefers is to read a disk, turn it into a filesystem image, and then synthesise flux from the filesystem image and write that to another disk.

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