PiDP-11: Recreating the PDP-11/70 | Hacker News Reader

PiDP-11: Recreating the PDP-11/70

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68 pointsjws39 comments

It's funny to see the nostalgia for that when I know people of the time who went to great lengths to get rid of the clunky bit interface. My dad built a pdp-11/34 and replaced the bit interface with a numeric keypad and some 7 segment displays. You still had to enter bootstrap code but you at least didn't have to do it bitwise!

Later he built an 11/70 and replaced the whole front console with a bootstrap terminal (with custom CRT driver if I remember correctly—ie, not off the shelf). That one you just had to hit the "boot" key and it would load the bootstrap code and do everything for you.

It just goes to say that current systems lack something. We cannot always put the finger on what it is and backtrack to where we think times were better. Using these machines is the closest real thing to going back in time.

I can see this with both powered systems like Symbolics LM or with smaller ones like PDP11, Spectrum, C64 or others: we lack the context in which they existed. We cannot bring them back today and use them as primary systems because we don't have the context that need those machines. They are doomed to be played a little and to be sent back to attic.

Current systems lack the context of the old times and old machines are frozen in a time that is not fit to today's needs.

It depends on how far into the past you want to go.

Not so long ago, my desktop was an IBM PowerPC running AIX with most (if not all) the heavy lifting being done on a laptop (that lacked a 2048x1576 22" CRT screen and a model M keyboard).

With X and an ethernet port, it was a perfectly usable machine, provided I logged on to the "server" on the other desk.

One of the projects I will do one day (no time now, sorry) is a board for Apple II's that would take over the bus and use the text mode and keyboard as the console of a Raspberry Pi-like board. It's perfectly doable to take over the 1 MHz bus and use the compute as Z-80 boards used to.

OK. That's not exactly usable as a work machine (not nearly as usable as the IBM, at least), but it'd be incredibly cool to be able to use a //e Platinum to work. Even if for a short while.

The exercise of traveling back in time is often not as much as to use the machines for actual work, but to experience them as tools to learn about the context where they existed - the time we had manuals printed in paper, where we would debug (and edit) programs on printouts on wide carriage paper with green bars - to (re)learn the lessons others learned before us that we can still benefit from.

The later PDP's had a built in boot system and you only had to enter by had if that malfunctioned.

The PDP11/03's had a monitor you could use to enter the code from a terminal VT52 or VT55

After I graduated, I built a PDP-11/70 replacement in FPGA to replace the controllers of old nuclear reactors. We designed it to be a fully compatible hardware drop-in replacement passing the full suite of tests with exactly accurate fault results. This included properly ordering floating point unit errors followed by a stack error -- due to pipelining the FPU error is supposed to be caught after the stack error. Additionally no other emulator exactly produced the same partial results of a division failing with an overflow.

How hard would it be to compile the HDL into C that could run in an emulator?

A couple years back I was looking into MESS code and observing how ordered it is and how much work would it be to do the reverse - starting from known modules (CPUs, CRTCs, etc) to compile it into an HDL.

My old college machine! Brings back memories of all the hacks it took to get anything useful written in 64K.

I knew it was history when I was in Los Alamos at a surplus store in the 90's, and they had one out in the rain in the parking log. Not even worth dragging under cover.

We got one for free from the Nikhef, the Dutch particle research center. Took forever to get it reassembled because it got banged around too much in transport but once it worked it was pretty neat. It came with a very good PCB routing and placement package, as well as a tablet and a graphics terminal.

That’s really sad. The PDP-11 is a great machine to learn assembler and architecture concepts on.

You can get Empire (http://classicempire.com)

for the PDP-11 here:

https://github.com/DigitalMars/Empire-for-PDP-11

I rue the day when I gave away my H-11. It's the background pic on my twitter account:

https://twitter.com/WalterBright

That's got to be one of the coolest RasPi cases in existence. And at $250 it may seem a bit steep but with the volume they made and the amount of time put in it is actually a steal.

Would love to build one, but with shipping and customs fees it’s going to be almost $400 sent to Europe. Maybe someone will come up with one I can 3D print?

That will likely require a lot of rework on the parts if you want it to look good. Especially the switches. And it still won't be cheap.

Even at that cost getting it to the UK I'm ridiculously tempted.

Funny thing psychology, I wont pay $1k for a phone, but $400 for a RaspPi case, thinking about it... :)

To Europe? The kits come from Europe!

I'd find this a whole lot more interesting if it was a real PDP-11 implementation.

It works with an FPGA based PDP-11 emulator as well: http://pdp2011.sytse.net/wordpress/things-are-moving/

I made something similar on a smaller budget, see jonatron.me . It's nowhere near as nice looking though. And you'd have to use a different emulator to make it do more than a couple of basic blinking light test programs

I've always wondered, what _are_ those large groovy switches on the front?

They're just numbered with integers [0..21, colored in groups of 3 presumably for octal]! are they seriously for bit flipping??

Yes: http://www.psych.usyd.edu.au/pdp-11/bootstraps.html

That's a "Front Panel" and all computers prior to around 1980 had one. It's the equivalent of the BIOS -- the one thing that's up and running when the power switch is flipped on. If the machine had core memory (which was non-volatile) the FP was seldom needed since the primary boot loader would be left in core long-term (after being toggled in once).

21 bits ... allows front panel access to more than the 16 bits of the machine registers. smokin'!

The /70 had a 22-bit address bus, so I assume that switches 16-21 didn't have any effect unless you were entering a memory address.

I read something that said Ken Olsen found these switches on an old model washing machine and thought they would be great on the PDP machines.

I think it might have been the 1957 Philco-Bendix Duomatic washer/dryer front switches that inspired the PDP-11 panel.

Yes. They are bit numbers.

nope you loaded code in as OCD octal coded decimal to boot the system if the bootstrap processor failed or was not present

Here's a demo of someone using these switches to enter and run programs on a PiDP-8.

https://www.youtube.com/watch?v=oMRDAD1JNWo

Give me this and anything close to an LA-32 paper terminal and I’d be in nostalgia heaven.

To use this do we have to put in the bootstrap sequence with the switches? :-)

Don't worry, the bootstrap code is muscle memory after a week or two of booting the system.

so true

I have an almost complete set of /70 parts in the closet, but no front panel. By the time I started buying parts people had realized the panels looked cool and were paying high $$ for them to make wall-art!

I actually built this kit recently. I'm now gradually building a collection of these front-panel-simulation machines. (Last year, I built his PiDP-8 kit.)

I'm only familiar with the altairduino, which works pretty well on my desk.

If you know of any other than those three, please post?

I think an IBM 1130 would be totally achievable and fun. A 360/91 might be a little optimistic. You can clearly see the influence on Star Trek original series in something like a 7090; someone who doesn't know retrocomputing would probably accuse a 7090 as being a trek prop.

I actually have an Altairduino kit sitting in my closet, waiting for me to get around to building it. :-)

So far, these are the only three kits I'm aware of.

At VCF-West for the past year or two, the Computer History Museum (in Mountain View, CA) has been showing off a similar project they've been working on with an IBM 1620 Jr front panel. However, that's definitely not something you'd make a kit out of. But, as part of it, they've figured out how to convert a modern'ish electronic typewriter into a teletype.

Apollo landing computer fit the bill? https://opendsky.com/

uMatrix has a horrible time with the crazy amount of bits and pieces to be temporarily approved for wix sites.

Not that I need to dive into 11/70 trivia... played around on them when my dad worked in Maynard, had front panel banks as rocket ship controls etc laying around the house. (Good times when your parent is on the bus test group and helping out on weekends :)

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