4 ms·
So.. back in the day, I used to do random PEEKs, POKEs, and CALLs, and there was one particular call that I stumbled upon that could quickly render a disc unboo
by mansilladev 6y ago
So.. back in the day, I used to do random PEEKs, POKEs, and CALLs, and there was one particular call that I stumbled upon that could quickly render a disc unbootable. Two questions:
1. Can you give it a try? It's CALL -20480
2. Anyone know what in the hell that one actually does?
It takes about a millisecond to render the disc useless.
- mattpharr 6y agoSo -20480 works out to be 0xAFFF. My trusty copy of "What's Where in the Apple", which includes a catalog of where everything is in memory, says that the routine to write the VTOC from its in-memory buffer to disk starts at $AFF8. The VTOC is the volume table of contents (https://en.wikipedia.org/wiki/Talk%3AApple_DOS#Volume_Table_of_Contents_(VTOC) https://en.wikipedia.org/wiki/Talk%3AApple_DOS#Volume_Table_...), so calling into the middle of that presumably ends up overwriting the VTOC with junk, which would indeed make the disk useless.
- StillBored 6y agoWithout spending much time on it, you probably jumped to DOS's RWTS or similar and wrote a track out (or something similar). That appears to be 0xAFFF which doesn't ring any bells but is roughly where DOS might load depending on machine/etc. Try https://github.com/iKarith/beneath-apple-dos/blob/master/ch05.txt https://github.com/iKarith/beneath-apple-dos/blob/master/ch0... for more info.