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You Should Have Voted For The PDP-11

Greetings from an alternate reality where DEC’s elegant PDP-11 architecture beat out Intel’s gross 8086 architecture, and DEC managed to gracefully evolve the 16-bit PDP-11 into powerful 32-bit and 64-bit successors, all while maintaining excellent backward compatibility.

Unfortunately, you’re stuck in your reality, so you have no idea what I’m talking about. Basically, your ancestors voted for the cheapest solution rather than the best solution, and now you have to live with the consequences.

The good news: PDPjs makes it possible for you to go back in time, and for a moment at least, and relive the PDP-11 experience. It’s still a somewhat primitive experience, but PDPjs is a work-in-progress, so hang in there.

The latest release, v1.30.3, adds the following features:

• Functional Front Panels (check out the demo below)
• ROMs such as DEC’s M9312 ROMs can now be installed
• Support for DEC’s RL11 Disk Controller has been implemented

To test RL11 support below, then select the “XXDP+ Diagnostics” disk from the “Disk Drive Controls”, click Load, and wait for the message:

Mounted disk "XXDP+ Diagnostics" in drive RL0

Then start the machine (click Run) and make sure the following prompt has been displayed:

PDP-11 MONITOR V1.0

BOOT> 

At the prompt, type “BOOT RL0”. The following text should appear:

CHMDLD0 XXDP+ DL MONITOR
BOOTED VIA UNIT 0
28K UNIBUS SYSTEM

ENTER DATE (DD-MMM-YY): 

RESTART ADDR: 152010
THIS IS XXDP+.  TYPE "H" OR "H/L" FOR HELP.

.

And that’s the extent of my testing, so if you try anything else and it doesn’t work, feel free to open an issue.

Better yet, fork the PCjs Project, debug the problem yourself, test a fix, and then send me a pull request. :-)

Finally, another shout-out to Paul Nankervis, who not only generously gave permission to use code from his JavaScript PDP-11/70 Emulator (v1.4), but has also patiently answered all my questions.

I’m @jeffpar and I approve this blog post.

Jeff Parsons
Nov 8, 2016