RL01 drive select plug and power supply questions

[Allison]

>
>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