Re: sys/dev/isa/fd.c FDUNIT/FDTYPE

[jnemeth%victoria.tc.ca@localhost (John Nemeth)]

On Sep 25,  9:46am, Tom Spindler wrote:
}
} Increasingly offtopic, but...
} 
} >      That must have been fun.  As I recall, this was basically the
} > Apple ][ disk controller squished into one chip. It was hard to call
} > that thing a disk controller since it wasn't much more then a TTL
} > driver and a shift register.
} 
} And a state machine as provided by one of the PROMs. A terribly complete
} analysis can be found in "Understanding the Apple II" by James F Sather.

     The PROMs on the Apple ][ only handled booting.  They didn't have
anything to do with the drives after booting.  The one other thing I
didn't mention was some kind of data discriminator to seperate clock
pulses from data pulses.  The hardware controller didn't even do the
GCR encoding/decoding, that was done in software.

     The code in the PROMs couldn't do much more then "recalibrate" the
head (basically move the head towards track 0 and slam it against the
stop a whole bunch of times due to lack of a track 0 detect switch),
read some sectors, and jump to the beginning.  One of the tricks I did
was to hack the first sector to make it ask for a password.  Combining
this with "copy protection schemes" that made the disk unreadable by
unmodified DOS 3.3 made for a fairly effective way to protect data.
Wouldn't stand up to anybody that truly knew what they were doing, but
beat 90% of people.

} >      My first experience with "operating systems" was basically taking
} > a printout of a disassembly of Apple DOS 3.3, figuring out how it
} > works, and documenting the entire thing, then mangling it to do various
} > tricks.  I wonder where that printout is?  I probably still have it
} > somewhere.
} 
} "Beneath Apple DOS", by Worth and Lechner, is probably a good alternative.

     Yes, I have that.  But, I learned a lot more by doing it myself
first.  Reading a book that gives you all the answers doesn't teach you
nearly as much.

} Both of the books I mentioned appear to be up on scribd these days.

     URL?

}-- End of excerpt from Tom Spindler