B9, CPM uses a single disk buffer to access the disk, and it is one sector at a time. In REXCPM, the bank switching is designed to make best use of what's possible in hardware. Disk sector size is set by hardware. Disk is either 2 or 4 MB.
It would be a challenge but not impossible to use REXCPM to test main rom images. REXCPM does not eliminate the main rom, it uses the option ROM space. So a main ROM would need to be modified to (1) ignore the option ROM socket as it WOULD be the option ROM and (2) ensure that the option ROM always stays selected and never accidentally switches to the real main ROM. Ultimately it would be easy to make a main ROM that runs as an option ROM. The original REX had an option to support main ROM replacement. I've dropped that feature from REX#, as it was a great way to brick your laptop. Steve On Thu, Feb 5, 2026 at 7:59 AM B 9 <[email protected]> wrote: > Stephen: I'm not familiar with CP/M or its editors. Were the sectors on > the disk used as a form of virtual memory pages? If so, it would seem that > having 16K sectors might be a disadvantage as only four could fit in memory > at a time. Does REXCPM let you tweak the sector size? How big is the "disk" > REXCPM offers? > > > Stephen: Since REXCPM is replacing the entire 64K address space, could I > use it to boot into and test a modified version of the main system ROM? Or > is there something different that would be better for that? > > —b9 > > > >
