PDP2011: A re-creation of the PDP-11 computer systems in VHDL | Hacker News Reader

PDP2011: A re-creation of the PDP-11 computer systems in VHDL

pdp2011.sytse.net

72 pointsljosa27 comments

DEC actually made a microprocessor implementation of the PDP-11 processor, called LSI-11. It has two chips, and is functionality equivalent to the large thing. Unfortunately, DEC was in a complete disregard of personal computers or workstations at that time, I don't think they made workstations with it. Otherwise it could be another legend in computing history: a PDP-11 workstation! Never happened.

Here's S100 computer board built around this microprocessor with a great introduction to the hardware details. http://s100computers.com/My%20System%20Pages/PDP11%20Board/P...

I had an LSI-11, in the Heathkit H-11 configuration. A wonderful machine. It's my background picture here:

https://twitter.com/WalterBright

Soviet BK series home computers were using the PDP-11 instruction set, which is probably the most beautiful part of PDP-11. 1801-series CPUs were slow as molasses though.

(In)famous for being 'middle-endian'

https://en.wikipedia.org/wiki/Endianness#Middle-endian

I used RSX-11M and I remember a few interesting things about it. First, it had an overlay linker: code would swap in if it used the same space as other unused code. Second, this extended to the operating system. There was a giant system build process where you linked all system programs in with the operating system. To run a command, it first had to be explicitly loaded into memory. So during this system generation process, you decide which commands should not interfere with other commands so that many could be loaded at once. Anyway, I remember it took many hours to run this process.

The 'M' means the system had virtual memory, but virtual address space was tiny- smaller than the physical memory space.

Johnny Billquist wrote a TCP/IP stack for RSX a few years ago and a webserver too. http://magica.update.uu.se/

The project lead for RSX-11M was Dave Cutler, who would go on and lead the creation of VMS, Windows NT, Hyper-V, the Xbox OS Hydra and a bunch of other things

Most systems of that era had overlay linkers. Added another bit of complexity to the builds.

I'm so happy to see an upswing in PDP-11 projects in the past year. It's such a nice architecture- very extensively documented, and from a time where it was possible for a programmer to really understand what the machine is doing, top-to-bottom.

Another rathole to chase down. If I could emulate an 11/70 but connect a real decwriter paper terminal, I’d be doomed.

You can use SimH for the emulation, which can direct emulated serial port to a physical one on your host. If your DECwriter has the EIA/RS-232 option, you're in business.

Weren’t all DECwriters, and just about any terminal from the 1970’s on, pretty much exclusively RS-232?

A lot of serial equipment back then still had 20mA current loop. For example, the ASR 33 Teletype[1], which was often connected to PDPs of its era did not have RS-232.

[1] https://en.wikipedia.org/wiki/Teletype_Model_33#Communicatio...

Easily fixed with an opto-coupler, a transistor, and a hand full of resistors..

Yes. Nearly every peripheral worked through serial ports.

You might say that the Serial Bus was nearly Universal.

Serial was ubiquitus but hardly universal. Loosing hours to the "change the baud, bits, reboot it" dance whilst bit-banging cts by shorting things with resistors, all just trying to get a terminal. Mating wildly different number of pins, pinouts and connector shapes whilst being mindful that some devices want -48v and others between 3 and 5, it was a frikkin' mess.

Lots of problems; big mess. So they unified things to a universal standard, whilst still keeping the spirit of serial alive. And by that, I mean wildly different plugs, different numbs of pins, incompatable pinouts, crazy voltages, drive issues and more. Truly the interoperable future is here.

(what? no, pass me _the_ usb cable. Idiot; it's the one that looks like the inside out apple cable. But not _that_ inside out apple cable, because although they're identical on the outside and will plug together....)

Anyone want to build an 11/70 with RSTS/E, send me a quote. I don't have the skills for this, but want.

There is another VHDL PDP-11 called the W11a: https://wfjm.github.io/home/w11/

One eventual goal is for it to be a PDP-11/70mP, a PDP-11 "quadcore".

BSD 2.x is tbe most insane OS ever. It is a backport from Vax Unix 4.x -- which used real virtual memory, often "lots" of it (2MB or even more!), 32-bit registers -- back to the 16-bit PDP-11, which had two (count 'em) 8Kbyte mappable pages in its 64K address range, and could swap 8 other pages into each. It came with all the same utilities as Vax Unix, except the networking bits.

We were so happy when we got a big -- 3" high, 6-platter 5.25" 20M -- Shugart disk. Didn't know we needed to recompile the kernel so it wouldn't swap in the middle of the fs (which had been at one end of the old 5M disk).

2.11 BSD is still maintained by Steve Schultz. Latest patch level is 451 released last year.

This is really cool, though I have never played with the PDP-11 architecture. When I first took computer organization and architecture at my alma mater, Wittenberg University, my computer science professor (Brian Shelburne) made us learn the PDP-8 architecture. I will never forget learning machine code on the PDP-8. He was very popular among the PDP-8 fan community as he developed two different emulators for the PDP-8 and published a few articles on using the PDP-8 in teaching computer science. He made an emulator for Windows DOS and later on a different one in C++ for Windows 7/8/10.

I'm so drooling at the idea of building a pdp-11 laptop right now!

Supposedly, this project was going to include pinouts for the mini-replica front fascia provided by Pidp-11...a pretty cool project itself: https://obsolescence.wixsite.com/obsolescence/pidp-11

Cool! Now let's make a FPGA clone of Super Sprint.

https://en.wikipedia.org/wiki/Atari_System

I can't get onto this site - just times out - anyone else ?

Yep. But thankfully archive.org has it. [0]

[0] https://web.archive.org/web/20190708094632/http://pdp2011.sy...

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