11 Sep
2022
11 Sep
'22
4:59 a.m.
On 9/10/22 21:40, Johnny Billquist wrote:
Yeah. It's actually a pretty horrible idea. RSX
have drivers for running
async DDCMP over DZ, but it's definitely one of those "if you have
anything else, you should probably use that".
However, the DZ do have SILOs. Otherwise it would run a high risk of
loosing characters. But it's still lots of input interrupts. But that's
not the really bad thing. Most (if not all) DEC serial line interfaces
do lots of interrupts on input. However, the DZ does it also on output,
which is the horrible part. Other interfaces, such as the DH does DMA
for output, which obviously is *way* better.
Many years ago I was responsible for a VAX-11/750 in a commercial
environment. There were about a dozen terminals in offices, and two
printers, all connected via DZ11s. That poor machine was SLAMMED with
interrupts. When I took responsibility for that system, one of the
first things I did was replace the DZ11s with a DH11. It was such a
huge system-wide performance impact that people left various nice notes
and treats in my office for weeks.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA