C70:info-cpm (07/17/82)
>From decvax!duke!uok!uokvax!mwm@Ucb-C70 Sat Jul 17 06:23:03 1982
Ithaca Intersystems (and others, from what I understand) have find what I
regard as a VERY nice approach to the problem of their BIOS not fitting on
the system tracks of a disk. They use a two level boot.
This works like so: Onto the system tracks of your disk goes a stripped
down version of the BIOS, with the some command hard-wired into the CCP
command buffer. This command (called startup by Intersystems)
overwrites the old BIOS, and then jumps to the cold boot entry point.
Viola, the new bios is running.
The advantage of this is twofold. First, you can have a HUGE BIOS (the
Intersystems caching BIOS is about 9K); second, you get to test your
new BIOS by invoking a com file, with no other magic.
The stripped down BIOS should be something useable. Instersystems takes
out the disk write routines. That way, if it doesn't boot the second
level, you can look around and see what went wrong.
mike