
Preserving a floppy disk with a logic analyzer and a serial cable - nynyny7
https://www.chzsoft.de/site/hardware/preserving-a-floppy-disk-with-a-logic-analyzer/
======
EvanAnderson
I read "Notes on Floppy Disks"
<[https://extrapages.de/archives/20190102-Floppy-
notes.html>](https://extrapages.de/archives/20190102-Floppy-notes.html>) last
night. It, along with this, really makes the technology seem much more
accessible to a non-electronics professional like me. These help make the
various floppy emulator devices I've got for my retro-computing habits seem
more understandable. (It also really makes me want to build some electronics
skills, too!)

~~~
blattimwind
Magnetic recording is kinda fascinating because it is conceptually simple but
very hard to do well. Conceptually all you need for a tape machine is two
small write coils (erase+write) and the bias oscillator. In practice the
"small coils" are complex precision parts. The circuitry of a Nagra is fairly
straightforward to replicate, but building comparable tape heads in your
workshop will take years.

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joezydeco
A related project that has been going through an amazing amount of progress is
the Applesauce Floppy Disk Controller.

HN Thread here:
[https://news.ycombinator.com/item?id=17256709](https://news.ycombinator.com/item?id=17256709)

IMO the coolest part is the widget they wrote to visualize the raw magnetic
flux on the floppy.

Example image:
[https://twitter.com/a2_4am/status/1026110390491643904](https://twitter.com/a2_4am/status/1026110390491643904)

~~~
molticrystal
While I am sure they released plenty of images on the project's site, as an
aside if you change the end of a twitter image url to ":orig", you'll get the
original unresized image.

In this case:
[https://pbs.twimg.com/media/Dj153frUUAEWAgx.png:orig](https://pbs.twimg.com/media/Dj153frUUAEWAgx.png:orig)

Really helps you visualize the details of the data, it is really amazing,
along the lines of those who look at nand gates and similar things to read
decapped roms and silicon circuits.
[https://i.ytimg.com/vi/RqmN7_KgbFc/maxresdefault.jpg](https://i.ytimg.com/vi/RqmN7_KgbFc/maxresdefault.jpg)

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userbinator
For those interested, the actual specifications of floppy disks are freely
available from the ECMA:

[http://www.ecma-
international.org/publications/standards/Sta...](http://www.ecma-
international.org/publications/standards/Standardwithdrawn.htm)

[http://www.ecma-
international.org/publications/standards/Sta...](http://www.ecma-
international.org/publications/standards/Standard.htm)

The standardese term is "Flexible Disk Cartridges", and the units are in
Metric, but those documents basically provide almost all the information
needed to build a disk drive or interpret the data on one.

The CD and DVD specs are there too.

~~~
markdown
> and the units are in Metric

As they should be. Why is this worth mentioning?

~~~
tom_
Floppy disks are typically measured in inches, common sizes being 8", 5.25",
3.5" and 3". Like any distance, these may also be measured in metric units.
However, for whatever reason, when it comes to disks, they pretty much never
are.

~~~
Wowfunhappy
Huh, is this true even outside the US? As in, did people in the UK call them
3.5 inch floppy disks, just like us Americans?

~~~
RL_Quine
Yes. Only a few things proliferate in inches, but products that are defined in
inches always do. Subway sandwiches are a mixture, in the netherlands they are
30cm (an extra 30mm), in other metric countries they remain as a footlong.

~~~
stan_rogers
30cm leaves you 4.8mm short of a foot. This is how we lose spacecraft.

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subfay
while impressive, I wonder where people take the time to explore ancient tech
in-depth. work, family, more work. how much time do you guys have?

besides, writing a n64 emulator, yes! fixing a decades old Sun, Xerox or VT
terminal, yes! emulating old 8bit cpus in JS yes!

but who wants to understand/explore a floppy drive?? no offense, curious
what's so interesting about floppy drives compared to typical retro tech stuff
I mentioned above?

~~~
llao
It's a hobby.

Other people care about collecting small colored pieces of paper, or tweak
their cars, or go on hikes, or paint.

~~~
djmips
No offense to OP (of this thread) but a lot of people who have an obscure but
intellectually stimulating hobby wonder why other people spend so much time
watching Netflix yet passing judgement on others as having 'way too much spare
time'. Is it really that alien to you to find this use of time justified? Have
you considered that they might be able to do this efficiently in balance with
the rest of their life?

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Aardwolf
So it seems it still needs an actual floppy drive, but controls it in a better
way to read it more reliably?

I wonder how hard it is to build something that reads the magnetic signal, or
what's left of it, directly from the floppy platter

~~~
rasz
It controls it in the same way PC controller does, the trick is in grabbing
raw data instead of relying on primitive hardwired decoders in descendants of
uPD765.

>hard it is to build something that reads the magnetic signal, or what's left
of it, directly from the floppy platter

Thats exactly what floppy drive does :)

~~~
Aardwolf
> Thats exactly what floppy drive does :)

I meant as a viable home project, doesn't have to be a fully functional drive
as long as it somehow allows to view the magnetic values, manually turn their
2D structure into the valid 1.44MB filesystem if necessary :)

~~~
rasz
Floppy drive does not decode disk data on its own, it merely amplifies analog
signal from magnetic head, filters and quantizes it (zero crossing).

[https://patents.google.com/patent/US4656533A/en](https://patents.google.com/patent/US4656533A/en)

What you get on a READ pin of floppy drive is the same information you would
probing read head (or rather preamp) using Oscilloscope. All you are
interested in is magnetic field flipping, zero crossing, encoded on READ pin
as an impulse.

Sure, you could precision machine turntable like contraption to do it
manually, but floppy drives are plentiful and practically free.

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jakeogh
Anyone able to recover 8" disks?

