4 Aug
2012
4 Aug
'12
7:35 p.m.
On 08/04/2012 09:53 PM, Fred Cisin wrote:
On Sat, 4 Aug 2012, Eric Smith wrote:
CP/M2 would use 5.5K for the CCP and BDOS, Likely less than 2K for the
BIOS and DDT needs 7K.
Since CP/M allows for overlaying the CCP you get 2K right there for use
at no real cost.
You would be left with very little free space for an application
(about 3-4K) but TRSDOS would
not be any better off with only 16K. Due to the 16K offset
applications were not portable
to the relocated CP/M unless reassembled or recompiled.
With 32K both become usable.
The TRS80 was unusual in that the first 16K was eaten up by LII basic
(12K), Video memory (1K)
and memory mapped keyboard (256 addresses) with many phantoms (minimally
decoded addresses)
in that first 16K. That limited the system to 48K of ram and would
later lead to bank switching
the first 16K with mapped ram.
Allison
Most if not all of the operating systems that
were intended to be
capable of running software for Model I TRS-DOS 2.x were capable of
running on a 16K machine, because they had to confine themselves to
basically the same memory footprint as TRS-DOS for compatibility. To
squeeze in the added functionality, they used more overlays, and in some
cases reduced the size of the resident code to make the overlay area
slightly larger.
FMG (relocated CP/M) would probably not have enough TPA to launch
DDT