
Visualizing Commodore 1541 Disk Contents - Luc
https://www.pagetable.com/?p=1070
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zantana
This guy
[https://twitter.com/a2_4am?lang=en](https://twitter.com/a2_4am?lang=en) has
been posting apple II woz files for a while and I know there is an Atari
format as well.

Cool stuff.

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squarefoot
One day we'll eventually run out of ancient drives that can read their
floppies, but the media could be still readable using other means. I would
love to see a plain scanner like device that reads magnetic fields instead of
light reflections, that is, something that slowly scans the entire surface of
the media [1] just like a scanner then builds a pattern of tracks and sectors
keeping track (pun unintended) of its position, then proceeds to map them into
data thanks to a database describing how data structure is arranged by
different brands/disk formats/filesystems/etc. We wouldn't need either speed
or realtime reading; being able to read and decypher an ancient disk in 3 days
of multiple passes to correct errors, would still make it a success. A (very)
small rotating head would likely work here. Did anyone ever attempt to do
something similar?

[1] The magnetic media should be removed from the disk body, that is, the disk
would stand still in the "scanner" while the head(s) would slowly do multiple
passes to map the remnants of its magnetic data. This would eliminate the
requirement for custom readers for very rare floppies, say like those 2" ones
I can't even remember where I saw them (possibly a musical instrument from the
80s).

~~~
pvg
What would the advantage of making the scanner completely unlike the actual
physical layout of the encoded data be? It just seems to make the thing more
difficult for no obvious gain.

~~~
squarefoot
I agree things would be initially difficult, but I don't see how we could make
a reader for less known disks without replicating their original drive
mechanics as well, which is probably the hardest part. To me it would be more
"scalable" to sample the magnetic field relative to the head position on a
plane (on which we fixed the disk), then building a structure where each 2D
element is mapped onto its position on the disk and assigned the value of the
magnetic field. The result wouldn't be that different from this project
pictures, but we could swap a 5.25 disk with a 3.5 one without changing a
single screw in the reader. A further development could be reading more disks
at once, provided their surface can be reached by the head. It would surely be
useless while we have working disk drives, probably not 20 years from now...

~~~
pvg
_building a structure where each 2D element_

It sounds to me like this is 'easier' because, I dunno, traversing arrays is
'easier'. But mechanically, serially scanning a disk or cylinder is much
simpler than serially scanning a rectangle. You can build a high resolution
scanner that isn't based directly on the original drive mechanism that but
still does magical high resolution scanning for offline analysis without the
additional artificial obstacle of making it like an image scanner.

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ggambetta
This is fantastic! Never used a Commodore, but this is familiar enough for a
DOS user from the 5-1/4" floppy era.

Would love to see something similar for ZX Spectrum tapes :)

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jackhack
Lovely visualization of knowledge that is only usually obtained through low-
level spleunking.

I'd love to see visualizations of some of the encryption approaches used on
the Apple ][, where sector alignment was shifted, file table indexeas moved,
data interleaving, etc. This was all possible due to the soft-sectored disks
and timings determined in software (Woz's genius move to reduce chip count!) I
could never wrap my mind around what was happening to the data.

~~~
jaxb
You can see some of those in
[https://twitter.com/DiskBlitz](https://twitter.com/DiskBlitz)

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nathell
Somebody make something like this for DOS floppies please. It'd be great to
see visualizations of normally formatted 1440KiB floppies vs. 1680KiB DMF
ones.

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sneakernets
C64 disks with custom loaders (read: games disks) were so fascinating to me as
a kid because the sounds of the 1541 drive would change as soon as that
fastloader code activated. Lots of game disks had their own unique loading
sound signature.

I would love to see a comparison of 80s floppy disk drives. Lots of genius
designs within... except the 1541's terrible bug which was never fixed due to
backwards compatibility.

~~~
pgrote
The copy protection on many games would cause "head knock" and force the 1541
out of alignment after a while. :(

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harrumph
Amazing, thanks for posting.

load "sysres",8,1

