
Kryofluxing PC Floppies - kencausey
http://www.os2museum.com/wp/__trashed/
======
fernly
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](https://en.wikipedia.org/wiki/KryoFlux)

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

------
gloflo
Be wary of Kryoflux:
[https://www.twitter.com/textfiles/status/1057997038154121216](https://www.twitter.com/textfiles/status/1057997038154121216)

~~~
grouber
That guy gets worked up about the strangest things.

------
snvzz
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/](http://cowlark.com/fluxengine/)

As an aside, for Amiga floppies specifically:

USB floppy controller for Amiga disks:
[https://github.com/jtsiomb/usbamigafloppy](https://github.com/jtsiomb/usbamigafloppy)

With an Arduino:
[http://amiga.robsmithdev.co.uk/](http://amiga.robsmithdev.co.uk/)

------
ansible
> _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.

~~~
userbinator
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.

~~~
chiph
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.

------
userbinator
_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.

------
tubetime
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.

~~~
PavlikPaja
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.

~~~
Dylan16807
> 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.

------
mirimir
> 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/__...](https://web.archive.org/web/*/http://www.os2museum.com/wp/__trashed/)
and Google cache link goes nowhere. I guess that they just don't want readers.

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

~~~
mirimir
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.

~~~
ksm
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.

~~~
detaro
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...

