Kryofluxing PC Floppies | Hacker News Reader

Kryofluxing PC Floppies

os2museum.com

55 pointskencausey21 comments

For those who don't know (as I didn't), Kryoflux is

> a software-programmable FDC system that connects to a floppy disk drive and a host PC over USB... reads "flux transitions" from floppy disks at a very fine resolution... the device operates on data bits at the lowest possible level with very precise timing resolution, it allows modern PCs to read, decode and write floppy disks that use practically any data format or method of copy protection to aid in digital preservation.

https://en.wikipedia.org/wiki/KryoFlux

Thank you. My initial guess from the title was some sort of fun hack to increase the storage density with cryogenics.

Be wary of Kryoflux: https://www.twitter.com/textfiles/status/1057997038154121216

That guy gets worked up about the strangest things.

While Kryoflux was first at dedicated hardware, it's worth noting a software solution using Amiga 1200 was used beforehand by softpres.org to low-level read floppies, and that there's open hardware alternatives to kryoflux today.

Fluxengine: http://cowlark.com/fluxengine/

As an aside, for Amiga floppies specifically:

USB floppy controller for Amiga disks: https://github.com/jtsiomb/usbamigafloppy

With an Arduino: http://amiga.robsmithdev.co.uk/

> I have come across one floppy (5¼″ low density, mass duplicated, circa 1990) where DTC reported a single track as unformatted and couldn’t read any data (there was just a bunch of zeros in the resulting image). That is, there were no errors reported at all, DTC simply decided the track wasn’t formatted. There certainly was supposed to be data on that track.

> Reducing the default RPM for decoding from 300 to 295 allowed DTC to decode all tracks of the floppy without errors, including the one previously seen as unformatted. I don’t know what that’s about.

That sounds like some kind of copy protection scheme.

Either that or a combination of being written at one end of the tolerance range for RPM, while being read in a drive at the other end of the tolerance range.

Many of the old 5-1/4" drives were low-fidelity copies of the original Shugart Associates drives. So speed differences and fluctuations were not uncommon.

Drives often have no media density detection and the density signal must be driven appropriately by the controller.

I seem to remember from when I briefly played around with this stuff, that the density select is used only for writing, to change the head current, but it's possible that the signal also alters something in the read path, e.g. the biasing/filtering for the head amplifier. Unfortunately I have been unable to find a schematic of a 3.5" drive to verify this.

Floppy drives are relatively "dumb" devices, they don't really interpret the data on the disks but just output a series of pulses corresponding to the flux transitions detected by the head. Data rate is entirely under control of the drive controller, which is what Kryoflux replaces.

it sounds like he's trying to use a high density drive to image double density floppies, which isn't a great idea. far better to use the double density drive which has the correspondingly large read/write head so you get a better signal/noise ratio.

It's a common myth that you can get less noise from bigger pixels. Smaller pixels only allow you to see more of it, as you can see higher frequency noise that you wouldn't see with the bigger pixels, but the SNR shouldn't be any worse.

> It's a common myth that you can get less noise from bigger pixels.

In general yes. Though having the wrong size read head gets in the way of doing perfect subpixel alignment.

But you're missing the critical issue with "double stepping". The head is reading half the width of each track, and then skipping all the way to the next track. It's not making two side-by-side reads on each track and combining the data. So if there's a small magnetic issue, it can corrupt bits that would otherwise be fine.

I’m pretty sure that issue is a question of 40 tracks vs 80 tracks, rather thsn the density.

The track format[0] of OS/2 is quite special.

[0] https://en.wikipedia.org/wiki/IBM_Extended_Density_Format

> Forbidden

> You don't have permission to access /wp/__trashed/ on this server.

That's not at all friendly.

Edit: Same via https://web.archive.org/web/*/http://www.os2museum.com/wp/__... and Google cache link goes nowhere. I guess that they just don't want readers.

Try changing your user-agent. This site is fussy about it and I guess it could be some sort of anti-bot protection.

Just Firefox here.

And just to be clear, it's not so much that I can't read TFA. It's how rude the message is.

Edit: Nope. Midori gives me the same error. They must be blocking VPN exits.

The site was just down for several days, apparently due to high amount of comment spam so likely that’s why they are now extra fussy about the what accesses it and where from.

The site has been block-happy for a long time. Every time it comes up on HN or Twitter, it's a gamble if whatever ISP I'm on at the time is in good graces right now. But I can somewhat sympathize, spam-fighting sucks if you're caught in a wave of it...

Safari and no VPN, same result.

I doubt it's intentionally rude - it's just the default HTTP 403 forbidden message from Apache web server (and perhaps some others.)

It's likely the site administrator didn't have time to set up a custom 403 page.

Reply on news.ycombinator.com