26 Apr
2007
26 Apr
'07
3:10 p.m.
From: "Dave Dunfield" <dave06a at
dunfield.com>
No, in most (but not all) CP/M systems, the CP/M BIOS is not dependant on
the boot ROM.
Unlike a PC, where the ROM contains more-complicated-than-it-needs-to-be
general purpose code to control all kinds of hardware, a typical S-100 CP/M
boot rom contained just enough code to read one sector from a drive and
jump to it. This goes back to the days of wildly varying S-100 cards...
The guy who wrote the boot rom (the disk controller maker) only knew for
sure how to talk to one bit of hardware in your system (his disk
controller).
---snip---
Hi
As an example, my IMSAI has no ROM at all and I run CP/M. The disk
controller uses DMA to the IMSAI's RAM. On reset, the controller will
transfer the first sector into the 0000 address of the IMSAI. I have
code on the first sector that loads the rest of what is needed for CP/M
and it then jumps to that code.
The controller was made by a company called Digital Systems and
does have its own state engine run from ROMs in the controller.
Dwight
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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?