mel (11/30/82)
The November 1982 issue of COMPUTER DESIGN has an interesting
article on the architecture of the DEC Rainbow 100. It gives
many details of the hardware and software design. But, it also
raises some questions:
1) The memory map of the 64K base RAM shows a 2K segment at the
low (0) end dedicated to the Z80 disk access buffers and flags.
In fact, the text claims that this memory is essential to permit
the Z80 to keep up with the disk data transfer rate. Where do
the CP/M programs load ? The DEC sales literature claims that
the Rainbow can run CP/M 80 programs, but most of these seem to
need to load at location 100, not up above the dedicated 2K
segment. Wasn't this the big problem with the early Heath
computers and the TRS-80 ?
2) The article and the sales literature claim that other
operating systems will run on the Rainbow. Obviously, MS-DOS is
the most suitable "other system" since it is the front running
system for the IBM PC. Will the Rainbow 100 be able to support
MS-DOS ? How ? Will it be possible to intermix CP/M 80
programs with MS-DOS programs ? or will each have to boot up
from their own disks ? (by the way, the much touted
"SOFTSENSE"R capability is just the selection of the Z80 loader if
a .COM file is given or the 8088 loader if a .CMD filename is given;
hardly a technological breakthrough)
3) Has DEC delivered any Rainbows yet ? I would appreciate any
comments anyone has about it, particularly how it performs with
standard CP/M Z80 programs. Thanks.
Mel Haas , houxm!mel