Visualizing Commodore 1541 Disk Contents

https://www.pagetable.com/?p=1070

by Luc • 7 years ago

126 13 7 years ago

pagetable.com

ggambetta• 7 years ago

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 :)

nathell• 7 years ago

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.

zantana• 7 years ago

This guy 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.

harrumph• 7 years ago

Amazing, thanks for posting.

load "sysres",8,1

jackhack• 7 years ago

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• 7 years ago

You can see some of those in https://twitter.com/DiskBlitz

squarefoot2• 7 years ago

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).

userbinator• 7 years ago

The technology to manufacture magnetic heads is not lost --- building a lathe-like drive on which any disk could be mounted and read doesn't seem like an impossible task. In fact, given that modern magnetic heads of the type used in hard drives can detect far smaller flux transitions, they could be used to "oversample" the original tracks for better accuracy.

pvg2• 7 years ago

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.

squarefoot2• 7 years ago

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...

sneakernets• 7 years ago

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• 7 years ago

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

Visualizing Commodore 1541 Disk Contents

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