24 Apr
2007
24 Apr
'07
8 p.m.
The problem
with either of those is that the ROM remains in the memory
map and takes up valuable RAM space.
Right. That much I get... so once CP/M is running, it's ordinary not
to refer to the boot ROMs? There's typically not a requirement to
keep some low-level BIOSy stuff in ROM? That certainly takes care of how to handle 64K of RAM
- just get rid
of the ROM from the memory map as soon as possible. With my other
experience with 8-bit micros, I didn't expect that this was a viable
techique. The systems I am familiar with pretty much require that you
keep the ROMs around - even with the C-64, which will let you bank out
ROMs and run from RAM, folks didn't tend to completely ditch the
Kernel ROM. Of course, Commodore machines don't have a "real"
operating system as such, and not even a DOS in the sense of an Apple
II or a TRS-80 - the routines in the ROM were commonly used by
applications like Zork that didn't care about BASIC, but they did care
that the ROMs had enough low-level I/O stuff to read and write disk
blocks, etc.
Again, think in terms of a box with a power supply and bus, and everything
else changable ... That was the environment CP/M was designed to address.
A C64 or any of a zillion other single-board computers have a much more
predefined environment, and often that environment is "software unfriendlty"
in order to make it cheaper - in such an environment, the ROM is much more
likely to be useful, and hence used by an OS or other system application.
Even so - It is not uncommon to completely eliminate the ROM and use OS
resident drivers once the OS starts up, as this saves space and allows for
a fuller RAM map.
A video card
will chew up valuable RAM, and many of them are only 16x64,
but it does let you do real-time screen updates, games etc.
Ah... now we are onto something - games... are there many games for
CP/M that require a video card, or were most happy with whatever sort
of TTY-type device (ANSI codes or not) was out there?