Re: I have a IIgs. So now what?

[dempson@actrix.gen.nz (David Empson)]

Tristan Mumford <xtristan.xmumford@xgmail.xcom> wrote:

> I'll have to dig the computer out of the shed one day. It's in a special
> padded carrybag with spaces for the keyboard and mouse. I seem to recall
> that it may also have the OS built into ROM.

That's basically true for all Mac models prior to the iMac.

The ROM contains a large chunk of the system software, including most of
the OS, file system and GUI code.

It won't work on its own, however - you need a bootable system floppy
(or hard drive) to do anything useful. The system software on the boot
disk includes some parts which are missing from the ROM, and patches to
various parts of the ROM code.

This is the same principle on which the IIgs toolbox firmware was based
- the ROM contains a basic suite of toolsets, but none of the file
system or OS code, just enough to bootstrap load a single sector from a
floppy or hard drive, from which the OS gets loaded. When you boot into
ProDOS-16 or GS/OS, toolbox patches and additional toolsets are loaded
from disk, replacing some parts of the ROM-based toolbox.

Application code generally doesn't need to know where a particular
toolset or function came from - it can be in RAM or ROM without
affecting anything other than performance (and memory usage).

-- 
David Empson
dempson@actrix.gen.nz