[Coco] CocoSDC booting OS9

[Bob Devries]

Hi all,

I don't have my CocoSDC yet.... (soon!)

I was looking through the NitrOS9 repo and found a disk image which can 
be used with it. I was surprised to see that even though it's a ~4.5MB 
disk, it can still boot OS9 without any extra disks.

Now that makes me wonder what the largest size a disk can be and still 
be bootable under the current boot method. The limitation would seem to 
be $0264 sectors for the sector allocation table, since the DOS command 
gets the kernel track from there (34 tracks * 18 sectors = 612 ($0264)).

Perhaps the "DOS" command could be made more intelligent by having it 
check the size of the disk by grabbing the first three bytes from LSN0, 
and then subtracting 18 sectors, and load the kernel track from there, 
thus putting the kernel out of the way of the sector allocation table, 
and thereby allowing for almost any size (hard) disk.

One gotcha would be if the file system used a cluster size of more than 
1, which would make the allocation of the kernel's sectors in the sector 
allocation table a bit more curly.

Chris Burke used a method by which track 128 of the drive was used as 
the kernel track, but IIRC it could be changed. He also had utilities to 
allocate the sectors in the sector allocation table.

My $0.02

Regards, Bob Devries
Dalby, QLD, Australia