Spectre GCR Manual Manuals - Atari Documentation Archive

Hard Disks and Spectre
Note that it isn't exactly even - for instance, you start at 30,004,
not 30,000.
To the operating system, these are all completely different drives
(say, C:, D:, E:, and F:). Only at the lowest level do the drives come
together on the mechanism. The hard disk handler does this.
When we ask for sector #1 of drive C:, we get physical sector #1 of
the drive. And when we ask for sector #1 of drive D, we get the first
physical sector of the D: "partition", #lO,002, off the drive. Similarly,
asking for the first sector of the F: partition gives us sector #30,004. See
how they're all put on one drive together?
There's a place where the "offsets" for each partition are kept;
that's the first sector of the hard disk. It's also called the "partition
table" and "boot sector". The data for the Hard Disk menu (starting
sector # and size, and type) comes from here.
Okay, shortly after Atari did this, Supra and other people came
out with huge hard disks, compared to Atari's 20 megabyte unit.
Given that we were stuck with 16 megabyte partitions because of the
GEMOOS typo, the most that a hard drive could hold was four 16
megabyte partitions - 64 megabytes total. Supra and JCD were already
selling 130 megabyte units!
So, Willie Brown and Mark White up at Supra came up with a
new partitioning scheme. (Yup, I'm just name dropping). You could
have up to 12 partitions per drive. And eventually they let you put up
to 32 megabytes per partition, with the stipulation that you only go
bigger than 16 megabytes if the use for it wasn't GEMOOS (e.g., wasn't
anything in ST native mode). The Spectre is a perfect example.
So, what we do to make the Spectre hard disk compatible is take
one, or more, of the hard disk's partitions, and first, mark it so GEM
never looks at it again. (For GEM to look at it would crash GEM, just as
reading Spectre format floppies crashes GEM). Next, we "stamp"
Macintosh formatting information on it - boot sectors, blank directory,
and so forth. Then, we're all set; the partition is ready.
As for you, next time you reboot your ST, that partition will have
disappeared from your Desktop in ST mode (depending on certain
things). If there was a disk icon hooked to that former GEM partition,
you'll find it either doesn't work anymore ("drive doesn't exist") or it
now hooks to the next available GEM partition, if there is one (e.g., if
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