rewriting legacy OS for new iron

From: Ed Kelleher <>
Date: Wed Sep 15 04:28:45 2004

At 06:54 PM 9/14/2004, you wrote:
>Yes, an 11/73 or /83
>would be 'snappier', but a bit more pricey, especially over an 11/23.
>I would love to find an 11/8x or 11/9x, but I'm not holding my breath.

I've found the 11/73 to be a LOT faster (subjectively at least) than an 11/23.
Sort of like the difference between 300baud and 1200baud CRT terminal
300 baud was painful on a CRT, but 1200 baud passed a knee, or hump,
and was almost as good as 9600.
At least as far as I recall from the time when VADIC came out with 1200
baud full duplex dial up modems we used to support DEC systems in the field.

The 11/73 has cache (16kb?), the 11/23 doesn't.
And while the amount is small, compared to today's standards,
it makes all the difference in the world, as anyone who has ever run an
11/70 with it's cache (8kb) disabled will tell you.

I did some testing on 11/73 vs 11/83:
The 11/83 has a faster CPU AND a faster memory bus.
You can use an 11/73 with the 11/83 memory to improve speed.
 From my website [WARNING: crass commercialism

To spare delicate sensibilities, here's an excerpt:

If your PDP 11/73 needs a boost, upgrading to a PDP 11/83 can give you 30%
more power with NO changes required to your software.
The 11/83 is a combination of 2 boards -- Processor and Memory:

The KDJ11-BF (M8190-AE) processor uses a 18MHz J11 CPU instead of the 15
MHz chip on the KDJ11-BB 11/73.
The MSV11-JE (M8637-EC) 1 MB memory board uses the C/D rows for a special
processor/memory bus.

Here are the results for a CPU/Memory intensive benchmark with various
combinations of CPU and memory.

1) KDJ11-BB 11/73 and MSV11-M (M7506) 21:32 (Minutes:Seconds) = 100%
2) KDJ11-BB 11/73 and MSV11-QA (M7551) 21:29 (Minutes:Seconds)
3) KDJ11-BB 11/73 and MSV11-PL (M8067) 20:40 (Minutes:Seconds) +4% Older
4) KDJ11-BF 11/83 and MSV11-QA (M7551) 19:28 (Minutes:Seconds) +10% CPU alone
5) KDJ11-BB 11/73 and MSV11-JE (M8637) 17:06 (Minutes:Seconds) +20% Memory
6) KDJ11-BF 11/83 and MSV11-JE (M8637) 15:04 (Minutes:Seconds) +30% Together

The benchmark was run under RT11. I created a VM: ramdisk, copied the RT11
SYS and SAV files to VM:, and another copy of the RT11 SAV files as .SAX
files and then booted VM: I executed a command file that printed the system
time, then did 100 iterations of a binary file comparison of all .SAV files
with all .SAX files and then printed the time at exit. Everything ran out
of RAM, there was no disk I/O.

Some of the KDJ11's on eBay are 11/83 processors with a "-xE" on the handles.

Be careful. The MSV11-JE can be used on 11/73, 11/83 and 11/84 systems.
The MSV11-JC can only be used on 11/84 systems.
Why? Beats me.

Also, the KDJ11-Bx quad CPU board has boot strap and console port built in.
The console port is isolated from the rest of the bus.
Some 3rd party QBus disk controllers use the console port for their
setup/formatting software.
You'll need a console port on the bus to use them,
like a DLV11-J, with port 3 set as console.
The KDJ11-Bx system will boot fine like this, ignoring the DLV11-J port 3

Ed K.
Received on Wed Sep 15 2004 - 04:28:45 BST

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