On Sun, Oct 30, 2022 at 2:49 PM Wayne S via cctalk <cctalk@classiccmp.org> wrote: > The difference between dz and dh interfaces is that the dh used dma instead > of interrupts to get characters to the cpu. It would be transparent to any > software. > I did a write up on them 40 years ago justifying the replacement of a dz with > dh saying that decreasing interrupts would increase performance on my VAX > 780. It did, but just a bit. To make a big difference, you’d have to have a > LOT of people banging away on serial terminals and rs-232 connected printers.
When I ran Unibus VAXen in the 80s every day at work, our small machines had 5-9 serial ports for 1-4 users and our largest machine had 57 serial ports (multiple Emulex CS/21 and at least one DEC DMF32 plus the console) and several dozen users. We never moved to terminal servers or other external connection management. It was all individual serial connections routed to offices and workrooms. I think our peak usage was 50-60 active users but at that point, the 8MB of physical memory started to be a constraint. I don't think the 11/750 could have handled that many users on DZ-11s. -ethan
