On Thu, Dec 31, 2015 at 3:40 PM, Paul Koning <[email protected]> wrote:
> DH/DHV/DHU have DMA output which means fewer interrupts. On a real PDP11 > with very high output demands, that can make a clear difference. This is an understatement. More over real DH's supported a DM11 which was full modem control, sadly the DZ had a half-way modem control. The designer (whom I will not mention by name) later messed up the original modem control on the console of the MC-500. It took a SW guy (i.e. me) to teach him how why all of the wires are needed. The downside of the original DH was that was a "full system unit" -- its was SSI/MSI TTL with the only LSI part being the Western Digital UART. Actually a very impressive design, but expensive to manufacture. The DZ was designed to replace it begin 8 lines per single board - so you got the same # of serial ports (16) in two slots, as opposed to entire system unit - but the system interface sucked and you lost modem control. > .... > But for most applications you're not likely to notice, and that's > especially true in emulation. Can't speak for RSTS or RSX but for UNIX it makes a >>huge<< difference. In fact Ken O of Able Computer made the definitive DH not DEC. His product was called the DHDM which was a single board with 16 lines and full modem control, could run all the DEC diagnostics and actually was a little smarter than the DEC implementation as he supported HW flow control which the original did not. Many (most) serious UNIX systems with his product, particularly when you attached things like "trailblazer" modem to yours system at 38K or more. A single DHDM with full modem control, cost the same as a single 8 line DZ; so it was a no brainer from a purchasing stand point. Although in defense of Paul, being inside DEC at the time, was probably hard to get the Able product; although I think I remember aps saying he had get a couple for decvax because the DZ load was killing them (aps I think you read this - do you remember/care to comment??). Which brings me a question for Mark and Bob? IIRC simh does not support the DH, only the DZ. I think I saw there was support for one of the QBUS DH's but not the real thing. If that's true, how hard would it be to make it support the regular DH? Clem *** Ken is someone I will add to Warren's UNIX people list at some point . BTW: At one point I got him to make a really cool product - which I think I have seen Noel also refer and ask about -- the Enable11 which was an UNIBUS cache card with a MMU on it, which he and I collaborated on (my first "published" paper - years ago). Anyway it allowed you to get 22 bit addressing on an 11/40 class system - did not solve the I/D issue, but was a major help for 11/34A systems (again adding that to simH would might make some sense. 2.xBSD will recognize it on boot and use it). As another side note, the DHDM was his biggest seller and a couple of years later, I also tried to get him to make a DHDM like card for the PC. At the time, he said that he could not figure out how to make money at it because add-in cards on the PC bus were so cheap. Eventually the Rocket Port guys did something similar with a custom ASIC and that became the serial solution for PC UNIX systems (I think I still have one in my collection of old stuff in the basement).
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