PiDP-11 Retro Computer Build - Computerphile

Before typed code, there was toggled code. We get hands on with a PDP recreation based on a Raspberry Pi.
The PiDP Project: bit.ly/C_PiDP11project
Aaron's website hosted on the PiDP-11 bit.ly/C_PiDP11
Thanks to Oscar Vermeulen for sending us the PiDP kits.
/ computerphile
/ computer_phile
This video was filmed and edited by Sean Riley.
Computer Science at the University of Nottingham: bit.ly/nottscomputer
Computerphile is a sister project to Brady Haran's Numberphile. More at www.bradyharan.com

[@spikeevans1488]

I was the system programmer for a PDP 11/70 running IAS (a derivative of RSX 11). The instruction set was octal because 3 bit fields worked perfectly for the 8 register cpu. Our system was used as an in-house time sharing system in a civil engineering consulting company. We had Vt-100s on 3 floors of our office building. I recall adding an in house email system and job accounting for charge backs. The Digital source code was superb and quite easy to hook into. This was one of my favorite architectures; it also made the transition to the motorola 68K very easy.

[@stephenwoods4118]

Be glad that you never had to mess with RSX-11M which was for some reason a bundle of spaghetti. RSX-11D was the predecessor to IAS. PDP-11s ran UNIX -V6 (I had a pair of 8" floppys that would boot and run on an 11/34 and ran V7 (and BSD 2.11 on a PdP11/44) and Unix -V7

[@markholm7050]

Spike Evans Not only eight registers, but also eight addressing modes. A two operand instruction was four bit op code, three bit source register, three bit source addressing mode, three bit destination register, three bit destination addressing mode. It made for a really easy to understand machine code model. Geez, even I could understand it. Octal was the perfect way to express and think about that instruction set. The whole business about ASCII in the video was a confusing red herring. Octal was for the instruction set, not the character set. PDP-11’s were fine with ASCII, in part because 8-bit byte addressing was native. It was easy to address and work with 8-bit data.

[@AaronJackson1]

Edit: removed gif, seems to be ok for now :) Yep, didn't take long! The PiDP-11 has crashed! There goes my plans of starting a web hosting company based on PDP-11s.

[@Aki-to]

Well, don't give up.

[@JarrydNielsenLMAO]

Can you run one emulation per core and do some kind of load balancing? if yes then please also add a 4-way 'KVM' switch. that'd be so cash

[@AaronJackson1]

@@JarrydNielsenLMAO Probably yes! :)

[@Sejiko]

oops i might have ddosed this machine by simple reloading the page a few dozen times... sry!

[@AcornElectron]

Jarryd Nielsen per core 🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣 yeah why not. Edited to say I wasn’t being off just amused at the idea of true multicore approach in a pdp 11

[@dwreid55]

This is a great kit. Thanks for the demo and for taking the time to record it. It brings back a lot of memories. I cut my teeth on the PDP-11 series machines. I still have a board or 2, some DECTapes and a bunch of stuff from the early machines, including a 90 MB CDC drive that is bigger than my coffee table and takes 2 people just to move it. My how times have changed. In the late 70s Western Digital made a set of 5 chips that, together, functioned like the LSI-11 chipset, and executed the PDP-11 instruction set. Since a 16 bit processor is limited to 64K of address space, any RAM over 64K had to be paged using instructions to an IO port on the memory cards. One quickly became proficient in Octal arithmetic as a necessity when configuring the machines. Thanks!

[@caw25sha]

My dad had a PDP11 which was brand new but damaged in transit. A friend who worked for Digital in Reading gave it to him and he brought it home with the idea of fixing it and getting it working. Which never happened...! Most computers at that time were just boxes but DEC made their hardware look like the those in sci-fi films of the era. Pink & purple: very 70s.

[@johnrayfield11]

I too built this kit, and also Oscar's PiDP8 as well. This has inspired me to create a panel for the HP 210MX, which I am currently working on

[@Vortexfugue]

Whoa, this took me back. I worked with the PDP 11/70 while stationed in the Air Force back in the 1970's.. they were fun, great memories.

[@AlphasysNl]

Hardware and software are so intricately linked, ofcourse you have to love them both. Well said.

[@smorrow]

Hardware is just ossified software

[@richardkramer3515]

Most of my programming experience was on IBM-360, but in the early 80's the company I worked for started doing some applications for the factory floor that required a PDP-11 (can't remember the model). I didn't get to work much with the PDP, but wrote some code on a VAX that would send requests to the PDP that would then control material movement out on the shop floor. I really loved the VAX (initially a VAX --11/750 then later a VAX-6000 and some MicroVAX workstations). I'm retired now, but just recently was thinking about the old days when computers had the big front panels with lots of switched and blinking lights and you could see by the patterns of blinking lights when the computer was doing what you expected or if it was stuck in some endless loop. I kind of miss those days.

[@RaymondHng]

So after working on PDP and VAX minicomputer systems, would you have wanted to go back to working in the IBM mainframe environment if the opportunity were to appear?

[@markholm7050]

In the mid 1970’s, the PDP-11s I was using at college ran chasing light patterns as an idle program on their time sharing operating systems. If the machine was active, performing a requested task, the front panel lights would blur, but when the machine was waiting for a request, it displayed the chasing light pattern. Each DEC operating system, I think even different major versions of OS’s, had a different chasing light pattern, so you could, if you recognized the patterns, tell which OS was running on a machine simply by looking at the front panel for a few seconds.

[@marccozziyammeringon9357]

Then in 1981-2 David Hasselhoff AKA Michael Knight of Team Knight Rider incorporated the rotating lights (RSX11M) in the grill of a Trans AM. Think the car also had DECTalk.

[@bryceletcher5326]

I learned all about basic computing on a PDP 11/05. This brings back memories!

[@sikkepitje]

How retro this is. Loading programs from tapes on my c64 now seems so comfortable compared to a PDP11

[@markholm7050]

Paul Wiegmans Only a really bare bones PDP-11 had to have more than a couple of words loaded at startup. An optional, but common, ROM boot loader required only one address and one instruction to be entered from the front panel in order to boot an operating system from a storage device. It was a few seconds work.

[@video99couk]

I rescued a PDP-11 back in 1999 that was being decommissioned due to the Milenium Bug in the software it ran. One got skipped before a collector could save it, but I got the other one to him. I hope it lives on.

[@thijshaker6451]

Forget Commodore 64's and BBC Micro's. PDP-11's it is! Let's bootup that sweet UNIX V7.

[@siddgangadhar1234]

Goodness! Soldering all of those components would be so therapeutic.

[@HendraKusumahiot]

the kind of therapy that some electronics engineer needed

[@lawrencedoliveiro9104]

7:23 No, the address register is incrementing by 2 each time (note the little gap where the units bit is 0). Machine instructions are multiples of 2 bytes in length, and have to be stored in even addresses.

[@marsgal42]

Every now and then I have a look around for old computer hardware. Real PDP-11s are in demand and their prices reflect it. My employers scrapped a VAX780. I don't have the room for one, nor could I afford the electricity bills. More recently we disposed of some Sun hardware, and literally couldn't give away several pallets of SPARCstations. I grabbed an Ultra 5 and amused myself by loading Linux on it.

[@dgillies5420]

Sun had an edict that anyone porting Linux to a Sparc was FIRED !! You're FIRED !!

[@dennisyoung4631]

Ultra 5 - 1995…. Solaris…

[@Seegalgalguntijak]

I've seen these on the VCFB - Vintage Computing Festival Berlin. Amazing little Kits, they were also available as a PDP-8 version. But unfortunately, I didn't have the money to buy one back then.

[@ZertiniK]

Engineeringphile looks promising

[@debjyotibiswas3793]

Why is that not a thing?

[@lawrencedoliveiro9104]

3:57 Notice the switch numbers up to 21? (The other end starts at 0.) The 11/70, while it was a 16-bit machine with a 16-bit “virtual” address space, had 22-bit physical addresses. It think it could handle up to 2MiB of RAM, not 4MiB--the other half of the address space was for accessing I/O devices. But the software couldn’t access the entire address space directly - it had to keep fiddling memory-mapping registers to map various 8kiB blocks of the virtual space to desired blocks of the physical space.

[@dgillies5420]

True, but that's why pipes in the UNIX shell could work so well. You could probably have a 64KB program 64KB of data, and then you could have 16 of these programs running at once in 32 separate 64-KB memory spaces = 2MB. They could communicate through the kernel or originally, UNIX used intermediate files to store piped data.

[@banderfargoyl]

Learned to program on an 11/70 running RSTS/E. The PDP cabinets were about 6 ft tall and formed a black wall with the CPU cabinet in the middle. On the left side was the magtape drive. And to the right, a pair of washing machine sized removable disc drives. The whole thing was enclosed in an air conditioned glass fronted room. At night, you could look into the computer center, and see the rotating lights on the front panel. But then they slapped a diagnostic panel on replacing the lights. 😪

[@lawrencedoliveiro9104]

An 11/70 was the main campus machine when I started my Comp Sci degree (1979). I learnt a lot from messing around on it--stuff that wasn’t even taught in lectures. Several of the lecturers seemed to have expertise elsewhere. For example, one handed out notes on how to do system service calls on a UNIVAC machine, because that’s all he knew. Which was completely useless, given we had no access to such a machine. Nobody gave a lecture on how to do service calls on RSTS/E - what a wasted opportunity, when there was an actual living, breathing machine running that very OS just outside the lecture hall, that the students could have run actual exercises on.

[@TesterAnimal1]

@@lawrencedoliveiro9104 yep. Huge, multi platter discs which held a whopping 32MB! I remember doing backups at Systime back in the early 80s.

[@recklessroges]

Toggling bits? In my day we used butterflies and neutrinos.

[@serkanmuhcu1270]

Is that an xkcd reference?

[@markholm7050]

The machines I used had a boot loader in diode array ROM that could boot to an operating system stored on a hard drive. All it required was toggling in one address and one instruction on the front panel switches followed by a switch that started at the loaded instruction. With a tiny bit of practice, it could be done from (human) memory in no more than 15 seconds. A single user operating system, RT-11, was up and running from a cold start in no more than a minute on a PDP-11/20, the earliest, slowest of the family. That was in 1975.

[@markholm7050]

Mike Enright That is quite possible. The point of the diode array boot rom was to avoid having to toggle in that first level loader, but if yours was inoperative for some reason, the front panel would get you going.

[@markholm7050]

Mike Enright I don’t know about 10’s, but on early 11’s I/O devices were memory mapped. It means reading from a simple sequential device like a paper tape, putting the results in memory and executing them would not really require a big program. The PDP-11’s auto-indexed Move instruction was ideal for this sort of thing.

[@dwreid55]

@@markholm7050 You are correct. The PDP-11 series had a completely orthogonal instruction set. Instructions could operate on data from any source or destination.

[@IdgaradLyracant]

What would be a great project is to set one up like a player piano, where you can load any code and then run it in a debug mode of sorts where it plays out the switch toggling that would have been needed to input the project it is executing.

[@karlkastor]

Damn, directly toggling bits, that's badass.

[@michaelsommers2356]

You had to toggle in the boot loader before you could read the paper tapes.

[@cesteres]

It's so cool with hardware debugger built in. Watching cpu registers directly.

[@Richardincancale]

We only ever used the direct key entry to load a short boot loader program that then loaded a more complex loader that read in the operating system. From then on you logged on like any other multi user computer - even type in Basic (or Focal-11 - the DEC version)

[@markholm7050]

That was my experience, too. Only had to toggle in one address and one instruction to get the machine going from a cold start, a few seconds work.

[@robinturner2300]

17773060 I seem to recall

[@HulIZ]

Don't forget that there are PDP-11's out there running nuclear power plants!

[@yereverluvinuncleber]

and they can never be replaced. My job is to keep them running.

[@jt9277]

It took me about 3 hours and I had a sandwich in the middle. Never change Aaron :)

[@hpottstock]

Aaaahh, this is so cool!

[@zedrem9876543210]

Aaron!!!! Looking good mate.

[@DrMcCoy]

I would have liked seeing a montage/fast-forward through the entire soldering process. I find stuff like that relaxing

[@Dominis.]

This should be used in schools

[@ian_b]

How to ruin your day: 1) Peel plastic off panel. 2) Immediately grab CMOS by the pins.

[@mohinderkaur6671]

That guy has a matching serial port connector on his ear too!

[@quadricode]

dreamy computer boi

[@bertblankenstein3738]

I have an M8192 processor board. It has two big ceramic chips and what appears to be a bunch of TTL logic. If have to look to see what exactly is on there. Might be a bit of RAM also.

[@AaronJackson1]

Cool! The M8192 is the 11/73, and is shown in the video previewed at the start of this one. It comes in three types, only the -YC has a floating point coprocessor iirc. They don't have any onboard RAM though, but should find yourself a 22 bit backplane, some RAM and an SLU or MXV11 card :)

[@KeithRozett]

What did the 22nd switch have to do with either octal or 8-bit bytes? I feel like there might have been a sentence or two of explanation edited out there.

[@peterfireflylund]

Look at the colours of the switches.

[@nomad325]

This is an awesome video, and im a huge Computerphile fan, but buddy... you gotta sharpen up that solder technique! Thanks for everything you guys do!

[@rj5529]

what did this nice boy do wrong?

[@LuisLascanoValarezo]

Hey guys, I was wondering if you could please do a video a a topic I'm so interested in. Linear Programming and simplex algorithm. Pleaaaaaseee. You are the only ones that I know that explain things with love. I ♡ CS

[@Android480]

How on earth did you get a webserver running on that thing? Did you manually enter the code or did you just install it to the Pi? I love the idea of having that thing sitting next to my desk and using it as a local dev server, that would be so fun.

[@BytebroUK]

I may be wrong on this, but I seem to remember that the terrain avoidance stuff in a Tomohawk Cruise missile was all running on a PDP11 motherboard.

[@robinturner2300]

Keith Willis several missile systems used the processor

[@S0ULEKS]

Nice!

[@user-vn7ce5ig1z]

You have to set it up as an LCARS. 😉

[@BlackBirdNL]

You talked about how 20 odd years later coding would have been different. The innovation!! Where's my Existenz jack in!?

[@First_Principals]

Could you do a video on the BBC micro bit from the 80's?

[@SG_01]

Looks like the website is already down :o

[@brostenen]

Cool. Just imagine writing a Unix kernal this way. 😁

[@oreste6076]

serial port for terminal???

[@MANU123423]

His website is already down lol

[@sebastianelytron8450]

He's a fraud.

[@MANU123423]

Sebastian Elytron why do you think that?

[@x3ICEx]

it is back up now

[@andljoy]

I want to watc somone type in the whole sorce code for unix on the frount pannel of a pdp-11

[@deckluck372]

What no magnetic core memory? :-) lol. I enjoy the blast from the bast and computing history videos.

[@tocsa120ls]

19:38: PiDP up, PDP down :)

[@billoddy5637]

Tell us about Block Ciphers

[@JohanDanielsson8802]

I am just a layman, and not a particularily knowledgeable one on this topic, but I have came up with a crazy idea which I would love to get an opinion on from the computer experts here. My idea, is a computer with one extra bit in every byte. The extra bit would not be counted into the byte´s number, it would rather mark the byte, as belonging to the computer´s own programming or not. The extra bits would stay in the computer - input and output cables should not have the capability to transfer the extra bits. When a new byte is programmed in or come through an input port, it will be given the extra bit. For example, the information you create when you type on the keyboard, or that come through some other entrusted input, could be marked as "green" with an extra 1 in every byte. Information that come from some not so secure input which you would expect to get attacked from - for example an Internet connection - could be marked as "red" with an exrta 0 in every byte. The idea - I do not have the competence to tell if it would work or not - is that only "green" code should be allowed to do some things, or that the anti-virus software should be able to recognize "red" code, and stop it from doing something it is not entrusted to do.

[@First_Principals]

CPU'S have EDB execute data bit which does something similar.

[@lukaszkonsek7940]

Shouldn't he start with resistors?

[@philp4684]

"If you wish to make a PiDP-11 from scratch, you must first invent the Universe."

[@lopa8519]

I've never seen holes like that on someone's ears ? What are they called ? Just curious

[@poke_champ]

Really? Many people in USA have it

[@SuperAWaC]

@@poke_champ not many people have it at all.

[@andrewkepert923]

Useful in windy weather. A couple of ropes and tent pegs and he's all safe.

[@dwreid55]

How common gauges are I suppose depends on where you live. I live near Chicago IL in the USA, I'm in my mid 60s (used PDP-11 computers a LOT) and I have at least 4 friends who wear gauges of various sizes. Some solid. Some hollow. His are rather stylish. I like them.

[@dgillies5420]

@@dwreid55 What you REALLY don't want to see if the process of enlarging the holes from a tiny pinhole into the size you see today in one giant enlargement move!

[@akuthia]

Looks like i was able to kill it some where between 30-50 connections

[@gz6616]

From the nose and below, he looks so much like Jacksepticeye.

[@spicytaco2400]

URL machine broke

[@ibycus314]

Would have appreciated more of an explanation of what part the pi is playing and what part your cobbled together hardware is playing in the loop, a look over the assembled board, etc.

[@oraz.]

He's running a webserver on that?!

[@nathanrcoe1132]

Seems funny enough just to do it, but the real question is can it run crisis :P

[@cycl0n31911]

Didn't know John Romero got rid of his mane

[@ConstantlyDamaged]

You're lucky you don't have any electronics engineers in here or you'd be getting flak about strain relief.

[@ConstantlyDamaged]

@ClickThisToSubscribe Bending the legs on components should be done with a tool that ensures no strain is placed on the junction of the wire and the inner parts of the component.

[@MelodeonTunes]

015757 - will write itself backwards through memory.

[@richardamullens]

MOV @-(PC), @-(PC)

[@robinturner2300]

Overlapped write, I used to teach a similar word overlap write to clear buffers without using variable space just using 3 field definitions

[@6872elpado]

I don't know I'm an engineer and I started following this channel because of numberphile. I understand everything on numberphile but I don't understand anything on this channel. Is this channel too specific?

[@robinbebbington7063]

Nope. I work in ICT and understand everything here.

[@6872elpado]

@@robinbebbington7063 Is this a serious answer? I had to google what ICT is. What I'm saying is that I am not a mathematician and I understand numberphile, but not this channel, meaning that in this channel they don't explain stuff as clear as in numberphile. I was asking if I'm the only one that is NOT working in the computer science field and I get an answer from somebody working in the ICT field? Of course you understand everything

[@robinbebbington7063]

Well I also trained and worked in Mechanical engineering for a decade and computer skills was a prerequisite so I guess it depends what you mean by an engineer. After all there is plenty of maths in engineering as well. If you are calling yourself an engineer I would be expecting at least a degree.

[@6872elpado]

@@robinbebbington7063 Who would call himself an engineer without a degree??

[@Creabsley]

I’ve met a few audio engineers who do.

[@wisteela]

Superb. Can the emulator be slowed down to actual speed?

[@PicaDelphon]

DEC 28,2020 ( 65,354 views )

[@jenesuispasbavard]

rip

[@ELYESSS]

It's already crashed

[@TheGreenKnight500]

"Omae wa mou shindeiru!"

[@markhaus]

It's crazy. The slowest pi made, running one of the slower languages made, running a program that emulates the PDP 11, is still faster than the real deal.

[@solderbuff]

Actually, the emulator software is SimH, which is written in C, which is pretty fast.

[@dgillies5420]

@@solderbuff I read the code and its really not that great. On a pi4 its 10x faster than a PDP-11 (6 MIPS) but it could be 20 MIPS with some tuning.

[@annyone3293]

1:00 рф :)

[@nadi4887]

can you do a video on RAID (Backup technology)

[@peanorg]

Raid is not backup! 🤓

[@damienw4958]

Haha, we already took down the server lol

[@Aki-to]

Say what

[@thehint1954]

We had a pdp- 1170 at uni running unix so I don't really get this video.

[@thehint1954]

Oh and we were programming in c

[@tobortine]

I can't help but feel your ear lobes were a bad decision.

[@tedarcher9120]

Кхем кхем. Мда

[@Sejiko]

oops i might have ddosed this machine by simple reloading the page a few dozen times... sry!

[@Kid420]

Firsttttt

[@jakegearhart]

This guy looks like Jacksepticeye in the thumbnail.

[@monkfoobar]

Superglue will fix those holes

[@Originalimoc]

Most painful to watch channel, why no auto-gen sub?

[@anotherdave5107]

terrible soldering skills

[@AshtonSnapp]

... does this guy have screw holes in his ears?

[@LKRaider]

I can't focus in the content through the gaping holes in his ears.