Re: DOS 3.3 Nibble Encoding

[mark@trillian.jsc.nasa.gov (Mark Manning)]

In article <Nov17.020819.75996@acs.ucalgary.ca>, sbdocker@acs.ucalgary.ca
(Sean Brendan Dockery) wrote:

[Stuff Deleted]

> First, the boot sector obviously conforms to the format of the rest of
> the disk.

This is not necessarily true.  If this were true, then the Apple could not
boot both a ProDos disk and a DOS 3.3 disk from the same disk drive (ie: a
5.25" Apple drive).  This is because one is formatted one way and the other
another.  However, even Apple ][s can boot into ProDos from a 5.25" drive.
Therefore, the boot sector has to its own format which is or can be
unique from the rest of the disk's format.  Otherwise, you would not be
able to boot a ProDos diskette from a machine which has only been reading
DOS 3.3 diskettes.  Nor would you be able to read Apple Pascal diskettes,
CP/M diskette, or any other diskettes which might come along.

Correct me if I am wrong, but I thought the initial boot track was more
or less a byte stream set-up.  Where there were a set of sync bytes at
the beginning of the byte stream and then there were just a set of bytes
with no sync information to them (sort of like reading a tape).  These
were loaded into memory and then the first byte jumpped to (which in turn
read in the next section and so on and so on...).

[More Stuff deleted]

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I saw a mountain rising.  Rising above the sea.  I heard the wind calling. 
Calling unto me.  Oh, who has seen the sunset?  Who has seen it rise?  Who
could ever be so blind?  As to never open their eyes? - Mark Manning

mark@trillian.jsc.nasa.gov