Author Topic: Decoding IBM PC cassettes  (Read 365 times)

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Online hamster_nz

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Decoding IBM PC cassettes
« on: October 14, 2020, 05:12:32 am »
I had a little bit of spare time and wrote something to decode an audio file containing IBM PC diagnostics.

If interested, you can find the source and an audio file at https://github.com/hamsternz/detape

It was more just for interest in decoding data sourced from an old 80s data cassette than anything else.

Currently just writes data to the screen, but looks like it calls BIOS ROM routines which are most likely no longer exist...

Gaze not into the abyss, lest you become recognized as an abyss domain expert, and they expect you keep gazing into the damn thing.
 
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Offline james_s

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Re: Decoding IBM PC cassettes
« Reply #1 on: October 14, 2020, 05:42:47 am »
The PC and later derivatives had BASIC in ROM, and most of the software stored on cassettes was likely written in BASIC so I'm not surprised if it appears to be calling routines in ROM.
 

Offline bw2341

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Re: Decoding IBM PC cassettes
« Reply #2 on: October 14, 2020, 05:04:42 pm »
Here’s VWestlife’s recent video on using the cassette port on a IBM PC. You can see the IBM diagnostic software running on the actual hardware.

 

Online hamster_nz

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Re: Decoding IBM PC cassettes
« Reply #3 on: October 14, 2020, 08:27:45 pm »
Here’s VWestlife’s recent video on using the cassette port on a IBM PC. You can see the IBM diagnostic software running on the actual hardware.


Oh, I could most likely use a screen-grab of that program listing to decode the line numbers and some of the BASIC tokens...

I think glancing in a tweet is what got me started looking at info on the IBM Cassette interface.
Gaze not into the abyss, lest you become recognized as an abyss domain expert, and they expect you keep gazing into the damn thing.
 

Offline bw2341

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Re: Decoding IBM PC cassettes
« Reply #4 on: October 14, 2020, 11:48:23 pm »
It looks like a short stub of program acting as a bootloader. Apparently, running the BASIC program restarts the cassette drive to load more data, presumably a  binary executable.
 


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