Re: ROM 01 Superiority

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

Rubywand <rubywand@swbell.net> wrote:

> Ken writes ...
> > 
> > When you run system software, there are two files on the system disk
> > (System setup folder) called TS2 and TS3.  A ROM 1 needs the TS2 file
> > (37 k).  A Rom 3 needs the TS3 file (40+k).
>  ....
> 
>      Weird! Never noticed that the ROM-01 patch file is _smaller_ than the
> ROM 3 patch file for System 6.0.1-- probably because I got used to the ROM-01
> patch being much larger than the ROM 3 patch (41k vs. 15k) in System 5.0.4.
> Seems odd that things should switch around for a later version of GS System.

This is purely related to the number and size of machine-specific
patches required in each file.  (There may be additional patches in
TOOL.SETUP which apply to both ROMs.)

ROM 3 contains almost exactly the same toolset versions as System 5.0,
so the 5.0 "TS3" file is rather small.  As you go to later system
versions, more bugs were fixed and features added in the toolsets which
are located in ROM, so these files grew.

Another factor is that ROM 3 has a lot more toolsets in ROM than does a
ROM 1, and the extra toolsets are the higher level ones which have
significant new features added from time to time.

This meant that the ROM 3 patch file tended to grow faster than that for
the ROM 1, and managed to overtake it by 6.0.1.

When System 6 was released, Apple decided that the patches required
would be too large to justify including them in TS3, so they forced the
disk-based TOOLnnn file to be loaded in several cases, completely
replacing the corresponding ROM-based toolsets (I think the Window
Manager, Control Manager and Menu Manager fall into this camp).

>      I guess in 1989 Apple was aiming for having GS System totally in-ROM.

Not really - they were just able to put a lot more of it in there by
doubling the ROM size.  This saved RAM and improved performance (no
overhead for memory refresh when executing code from ROM).

They couldn't put the entire toolbox in ROM, because there wasn't enough
space and they didn't want to include any code specific to any operating
system (GS/OS) in ROM.  This meant that some toolsets (such as Standard
File) could never be in ROM, and neither could selected calls from other
toolsets.

Another possible reason for including additional toolsets in ROM is that
it meant that booting a System 4.0 or earlier disk on a ROM 3 would use
the newer ROM-based toolset rather than the older disk-based one.