Re: DOS 3.3 Nibble Encoding

[vandry@CAM.ORG (Phillip Vandry)]

k_bouchard@csc32.enet.dec.com (My name is...) writes:

>Am I out in left field on this? All this verbage to explain something basic? I
>always thought that *any* computer boots from sector0-track0 because early in
>the boot process of *any* computer,a RESET signal is sent out on the computer's
>I/O bus (or whatever bus the various controllers sit on) and this "RESET"
>results in all registers being set to zero. (including both sector and track
>registers) 

There's no such thing as track and sector registers. Reading a track/sector is
more complicated than setting a certain register and all of a sudden the
track is read! :-)

But it's quite similar to what you say. As soon as the Apple's power supply
starts delivering operating voltage, RESET is pulled high and the
microprocessor initializes itself. Then it runs a firmware program at a
predetermined location. This program puts a startup message on the screen and
determines the boot slot. Then it transfers control to that slot's firmware.
The disk II firmware reads track 0 sector 0 at $0800 and jumps to $0801. This
code does different things depending on the operating system.

-Phil