Dec Rainbow prehistory

On Thu, 20 Nov 2003, ben franchuk wrote: Well, kind of. The DECmate II (and, I believe, the III; I never used a III) could accept a coprocessor containing a Z80. The only I/O resources directly available to the Z80 were registers used to pass messages between itself and the PDP-8; the PDP-8 did all the I/O. While I had to give up on the Rainbow because it was not good enough as either an MS-DOS or a CP/M machine, the DECmate II is one of my all-time favorite CP/M machines. I knew the Rainbow was in trouble as an MS-DOS machine when I had to trade my newer version of Turbo C for a friend's older version because the *command line* version of the compiler had too many dependencies on the IBM PC ROM BIOS. It was all down hill from there. As a CP/M machine, I had to give up on it primarily because the Z-80 didn't support the I/O byte. At the time, the sort of dorking around I was doing with CP/M involved serial communications of some sort; playing about with serial mice, drawing things on a Tek 4010, communicating with the VAX on which I did serious work, etc. All of these were done by fiddling with the I/O byte on all of my CP/M machines *except* the Rainbow. Consequently, I could write a program and use it on my Kaypro, Epson Geneva, even the DECmate II; but *not* the Rainbow. I even had a two-user experimental MP/M setup in which the XIOS sat beneath the CP/M BIOS using the CP/M BIOS services for all I/O, which included diddling the I/O byte to perform console I/O for the two users. Didn't work on the Rainbow. I never got attached to CP/M-86 because I didn't have development tools or programming documentation for the system. In fact, my primary method of using the Rainbow was to load my CP/M-80 TSR that gave me command line recall and editing, which meant that from then on I could only run Z80 programs. Consequently, the Rainbow's deficiencies as a CP/M-80 machine were fatal for me. Oh yeah. The console I/O on the Rainbow was also slow. Not as bad as the Pro, but the DECmate II's built-in terminal emulation was peppy. -- Roger Ivie rivie(a)ridgenet.net <input type crash>