Dec Rainbow prehistory

On 11/18/2003 01:23 AM -0600, Tom Jennings <tomj(a)wps.com> wrote: Tom wrote lots of good things... Well, I won't defend the quirks of the Rainbow... (more later) But you're forgetting that the Rainbow 100A design pre-dates the IBM PC, it was first designed as a CP/M machine. MS-DOS came later. And IBM put interrupts on the PC in places that Intel's data sheets documented as RESERVED! IBM did not pay attention to Intel's recommendations and violated a few of their support device allocations. DECnet-DOS was developed in the DECnet group inspite of the Rainbow group at first. Their marketeer felt that Corvus Omninet was going to be the big thing. Only later did we integrate when they got into LAN Manager support. Our first target was the IBM XT with a 3Com 3C501 Ethernet board, and the Rainbow running DDCMP on the serial port. We weren't going to wait for the Rainbow-150 which would be a more industry compatible system. When the IBM AT appeared, that scotched the RB-150 and lead, eventually... to the VAXmate. (Thank KO for the delays) I remember the MHFU watchdog and the Vertical Retrace Interupt. The DECnet kernel basically ran as an interrupt driven background TSR. On the IBM PC we easily shelled off the 1C clock tick, but on the Rainbow, we had to build "clever" reentrancy shells around several interrupts to avoid some wierd stack overflow or reentrancy into the video BIOS. The Rainbow at least had a decent UART with a multicharacter FIFO. I had no problem doing 19.2kbs using C routines. That stupid XT UART could barely do 9600 with an optimized state driven assembly routine. UART FIFOs didn't appear until the IBM PS/2 Model 50. Dave (has two HP16Cs and runs the wprn program)