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Comment by mjg59 | Hacker News Reader

Despite the punchline, the USB floppy spec is actually incredibly restrictive and only supports 720K, 1.25MB and 1.44MB formatted capacities. This means, ironically for a spec partially written by a friend of Raymond Chen's, that you can't read the Microsoft 1.68MB DMF floppies used for software distribution with a USB floppy, but it also means that it's impossible to support the older 400K and 800K Mac formats. To be fair, those formats also require a special drive mechanism (the disk spins at different rates depending on which track you're reading), but there's no way to expose them within the USB floppy spec. There's an entirely justifiable argument for manufacturing a separate Mac drive with different functionality and requiring its own drivers.

(Edit to fix capacity)

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Most USB floppy drives you can find today support exactly one format - 1.44MB disks. Reading older 720k disks has become a challenge. I bought a small pile of Dell laptop internal floppy drives from eBay because they (slightly oddly) have a USB port on the back, and still support 720k.

By the end of the floppy disk era, it was very rare to find a 400 or 800k disk that was still working, and Microsoft really didn't make much use of the DMF disks, they were replaced by CDs very quickly.

I still have a pair of USB floppy drives hanging around with the hopes of getting some more inexpensive ones at a flea market some day to make a USB based RAID-floppy array. I bet it will sound amazing.

If you ever do I hope you post it here!

It will never be as cool as this guy, https://silent.org.pl/home/2022/06/13/the-floppotron-3-0/

I still have a bunch of 400k and 800k disks that work fine

Yes me too. I recovered a lot of them. Even ones from the late 80s.

That's a story people tell, but I'm not sure how true it is. There is tons of Amiga and older Mac software out there on floppy that you can still read just fine.

Of course it's still a good idea to get a Greaseweazel and back up everything you come across.

Yes it's very hard to interface a 360 kb floppy to USB. I found an interface but they refused to ship that outside the US. Eventually i found the greaseweazle which needs special software but it works great. And that was available here.

I would think that the most 'bare metal' way to read a 360KB floppy these days would be to use a vintage 2000 or 2001 x86 PC motherboard/cpu/RAM combo that has the standard onboard floppy drive ribbon cable header, and attach a real 360KB drive to it. Or a more 'modern' 1.2MB half height floppy drive that's known to be able to read 360KB disks.

If you find something with like a Pentium 3 1 GHz on it, it should be capable enough and with enough RAM to boot a new i386 linux kernel and userland environment, while still having direct hardware access to the FDD.

I would be surprised if you needed anything that old. I was doing some research on my 2012 vintage PC mainboard a couple of years ago, and seem to recall a reference to the chipset one generation prior supporting floppy drives. Of course, whether many mainboards actually included the header is an open question. I also have a Pentium 4 laptop hanging around that has a swappable drive bay that could use a floppy drive. Of course, finding the appropriate laptop floppy drive will be difficult.

PCs were slow to drop support for legacy hardware.

Yes you probably wouldn't need to go that old. As I recall Pentium 4 motherboards of the generation around p4 "northwood" and "prescott" still had floppy drive headers commonly built into them. Probably there's some motherboards that have FDD headers and are also new enough to run an AMD64/x86-64 understanding CPU to run a current linux kernel without having to hunt down i386-everything for the operating system install.

I think my AMD Sempron 3100+ PC has an FDD header, and it can run x86_64.

> but it also means that it's impossible to support the older 400K and 800K Mac formats

I'm trying to remember, but was it even possible to format or read 400K or 800K mac floppies on a machine that came natively with a 1.44MB drive such as a Mac SE/30 or all the other post-1990 Macs?

Yes, SuperDrives (and the SWIM and New Age controller chips) can do GCR discs. Mac OS 8 removed support for the original Macintosh File System though, so they’d need to be HFS formatted after that.

Yes, every floppy equipped Mac had the ability to read/write 400k/800k discs via the SWIM chip. Even the first couple revisions of the iMac G3 had it.

At least these days you can get boards like the GreaseWeazle that can convert these drives to read any floppy.

Although these read them "raw", I'm not sure if anyone has written a device driver to use these as ordinary floppy drives, though it would definitely be possible.

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