21 Oct
2005
21 Oct
'05
8:57 a.m.
Subject: Re: RL01 drive select plug and power supply questions
From: Paul Koning <pkoning at equallogic.com>
Date: Fri, 21 Oct 2005 10:58:55 -0400
To: cctalk at classiccmp.org
Allison> Yes I do. However for a single user system the load is not
Allison> an issue. If your running a timeshare system such as RSTS
Allison> or RSX with more than one user then DHV11 sense as well.
Not true. 9600 baud is 960 interrupts per second, on a character I/O
device. That's a big number for a PDP-11. Output will be
significantly less of a burden with a DH type output controller than
with other types -- even for just one active terminal.
Depends somewhat on the OS. It dont know about you but most people
can't type much faster than 100WPM (less than 10 chars sec).
For RT11 it's mostly unimportant. For unix (the most sensitive
to interrupt loading you _may_ care as a single user).
Allison> For most of my 11s four lines is the limit
for what I can
Allison> seem to keep busy. Figure a user terminal, LA100 Printer
Allison> and serial line for modem or data line to another system. At
Allison> the extreme I've run two terminals for OSs that support that
Allison> but, I can only type on on at any instant. ;)
Sure, if you're mostly doing editing, then the CPU burden of high
speed output may not be obvious. If you had an LN03 or similar
printer, you might see it more easily. An LA100, of course, isn't
much of a problem because it is quite slow.
Actually printers are a bursty load (fill the buffer and go away)
and I've found that in practice the faster you fill the buffer
the better (high line rates or use a parallel interface).
Actually try this config.
11/23B
256kW ram
RL02
RX02 x2
DLV11j terminal lines at 9600
DUV11 running DDCMP (DECnet phaseIII at 19.2k)
LPV11 (modifiedto match dataproducts interface) with
LN01/LN01S 12ppm printer. Later the LN01S was
replaced with a DLV11 (same address) and LN03.
RSTS (later RSX)
3 users
Typical task load was BASIC (modeling program for reliability),
calc, Text editing (word-11) and edit and a cardfile database
written in BASIC. Also we had preLAT software for the 11 to
take local printing from the VAX.
Performance was good enough that we used that over the VAX
(line lengths limited us to 2400baud in our part of the mill).
That saved the VAX for email via the DUV link or direct. Later
the DLV11j was replaced with a DHV and there was no noticeable
performace improvement. It was a strange config but it helped
us develop, sometimes test and support the up and comming printing
products. We later moved to a VAX750 and found it not much faster
as a user perception.
One of the strong points of the -11 is it's interrupt performance
compared to a lot of other machines. Not to say there wasn't a
point where the loading wasn't noticable just took a bit to get
there. The users noticed the modeling program the most as it was
heavy on the calculations, more ram and an 11/73 would have helped.
Allison