below.. On Thu, Apr 4, 2013 at 5:28 PM, <Paul_Koning at dell.com> wrote: I thought DZ11s were around back then. They are just becoming popular in the early 1980s, but is possible they were around by 1979. But Cory is using VMS 1.x. I'm trying to remember, we had VAX Serial #1 at CMU in 1977/78 - which ran VMS 1.x of course. It must have been connected to the original "CMU Front End" which were dedicated PDP-11s, filled with DL11s and CMU ASLI's. Originally, which Front End machine dedicate which systems you saw. The connection between the host to the front end was parallel port, it must have been an DR-11B's back to back but I've forgotten what that HW was (boy those bits have rotted in my memory). But if not, the DH11 sure was, 16 lines, DMA output. And unless you used Able Computer's clone of it the (DHDM), a full Unibus "system unit" of TTL hardware. What a beast, but full modem control that the DZ did not do and actually could drive the lines without killing the processor., which DZs and DL/KL's did. But that's for terminals up to 9600 baud. For networking, you'd use a DMC-11 unless your OS supported the cheaper devices and money was that tight -- that one goes back to about 1976 and delivers up to 1 Mb/s depending on model (up to 56 kB/s long haul, given suitable modems). Hmm - are the DMC and DMR that old? I remember fighting the firmware in the them to allow high speed serial networking. They had a dedicated microprocessor on them (8080A or 8085 IIRC - but it may have been something custom). They were expensive, which why Berk-NET used 9600 baud serial lines, until we got 3COM & Interlan Ethernet cards at Berkeley in 1983. CMU would get Xerox 3Mhz Ethernet cards for many of the Vaxen and 11s in the 70s when it was still just Xerox. What would become the Cisco Router has it origin in some work using PDP-11's and Xerox cards to create the "distributed front-end" - which allowed more terminals to be connected to N machines and you could get to any system that was on the any of the front ends. It was all very cool and bleeding edge. Lots of terminals with single line interfaces would be really ugly. Amen. DZ's were not much better either, because the interrupt rate at 9600 would like a 1MIP Vax. But I do remember our college main timesharing system, in 1973, a PDP-11/20 with 28 kW of memory, RSTS V4A, and 16 terminals on 16 separate KL11 or DL11 interfaces. Oh yes, and a mean time between crashes of about 1 day. Are you sure it was a 11/20, not an 11/40? I did not think RSTS could run without the MMU. With 16 DL/KL11's even with an 11/40 the interrupt rate had to been wretched. That said, in late 1979 when I was at Tek Labs, I took an 11/70 and put 96 serial ports of Able DH/DM into it. Amazingly enough that V7 Unix box provided more cycles to more people than the CDC Cyber it sat next too in the machine room. Clem