PiDP-8 tour and demo

After much physical assembly, I can finally do some software assembly.

[@steve-si3oz]

In the mid 70s, I ran an entire city newspaper 60K circulation on a PDP-8e. We did both circulation and accounting by keeping it running 16 hrs per day. I was the programmer and I had three operators. . .. These computers were real workhorses.

[@josephgaviota]

We had an 8e in 1975; and were one of the largest paperback book composition houses. Paper tape in, paper tape out. No terminals of any sort (VDT or TTY). Does anyone young even know the term VDT any more? And, do they know a Teletype was _the_ system console for at least 20 years?

[@phaecops]

What did you use as a programming language and editor?

[@teacupanimates]

⁠@@phaecopshearing that he said the mid 70s, definitely would be BASIC language, and they used terminals to interface it, as it was a mainframe

[@JackRussell021]

When I first started college, we had some of these machines. I recall a game that we had where it would take 3-letter words and it would randomize them - you had to type in the actual word, and one could get very quick at it. I suggested that to make the game harder that we replace the vocabulary in the game with PDP-8 assembly mnemonics - others thought that this would make the game far to hard, so I never actually did this. The joke we had was that the one instruction that sounded like it might be real but wasn't was "Excrement and jump on zero". I recall paper cards with assembly quick reference that we could use to quickly look up instructions.

[@donblack4521]

Back in the late 60s and 70s I worked in a semiconductor manufacturing plant where many machines like this were used to control parts sorters, device testers and data collectors etc. My job was repair and maintenance, but I had many opportunities to write programs that made my job faster and easier. These machines were a lot of fun to play with, my compatriots and I regarded computers like this to be the ultimate toy. As microcomputers and and semiconductor memory came into general use these machines sadly began to appear on junk piles and in salvage yards. Time and technology march on.

[@woodwaker1]

These were part of a Computer Output Microfilmer, that controlled all of the processes. I was hired to maintain and run these in 1973. These were fantastic for what they did, the only real problem was the contacts of the boards and Unibus. We continued using them until 1991. I purchased used units for replacement boards, complete used units were cheaper than buying a single new board.

[@liamconverse8950]

Using these things seems like such a pain Im curious what it was actually useful for

[@donblack4521]

@@liamconverse8950 These computers were often embedded in electronic equipment used for such things as semiconductor test and sort, process control and data logging. The PDP8S was very simple machine that executed the PDP8 instruction set, but cost less than $10,000. In the 1960s and 1970s, thousands of linotype operators that worked for magazines and newspapers got replaced by PDP8 computers. This was the point in time when computers began to take over many mind-numbing tasks in science and industry.

[@Anonymous99997]

In the 70s my high school had a PDP 8e with a Teletype terminal with a paper tape reader. To start her up we had to manually enter an assembly language program into memory via the toggle switches. That program merely taught the machine how to communicate with the Teletype. At that point we could then load the OS using the paper tape. The language was FOCAL, I believe.

[@connomar55]

Removed 2 of these from a London Hotel in 1980. It had 10 years on the timer. Consisted of a paper tape reader and a 500K byte fixed disk hard drive. Also an intercommunication system so it could work in tandem with a second system which it used for redundancy. Have pictures if anyone interested.

[@tickertape1]

Interested

[@raystone4673]

If that hotel was on Oxford St, I stayed there in April 1974 after doing PDP-11 hardware training in Maynard Mass. The machine was visible from the foyer front desk in thru a doorway while checking in.

[@gregorymalchuk272]

What were they being used for?

[@connomar55]

@@gregorymalchuk272 Front of house hotel system. Did the billing, check in/out etc as far as i know

[@gregorymalchuk272]

@@connomar55 Wow, a hotel was using a minicomputer for routine stuff like that in 1980? Do you suppose was the rule or the exception at hotels and businesses of that size as of 1980?

[@sergeypokrovski3240]

This must be what it's like to pilot the original Enterprise.

[@kckoellein]

😂🤣😂🤙🏻

[@kerryedavis]

Putting main programs or data at addresses 10-17 is pretty much a no-no because those are the auto-increment addresses. References to those addresses by "indirect" addressing has the contents incremented first, so they were reserved for that specific need. Address 0 is reserved because that's where Interrupt routines start. Indeed, all of page 0 is reserved since it can be accessed from anywhere else in each 4k field. Typically, programs started at 0200 octal, which is the first address outside of page 0.

[@tech10171968]

I never touched one of these, but this reminds me of the computer I did work on while serving in the Navy. It was a Univac 1219, otherwise known as the Mk 152 computer, and was the brains behind the Terrier missile system in those days. Looked just like this but was the size of a refrigerator. Look it up sometime and be amazed at just how far technology has come since those days.

[@Jimo368]

A machine like this was my main focus in college in 1979.

[@johncherry108]

This brings back a lot of memories. I used a PDP-8 in the early 80s, but it was a PDP-8A with a keypad instead of toggle switches. Same instruction set, though.

[@renehoude96]

Oh wow. I work 24 years for DEC. I was the Canadian tech support for the PDP 8 line. The RIM Loader on the Front Panel. This is the small program to load application program. The first two code: 6032 (read the paper from the Teletype) 6031 (confirm reading) 5357 6036 ( read the info to memory) All the loading to start other application was all done by paper tapes. So many good memories😀

[@williamdegnan4718]

Thanks for a trip down (ahem) Memory Lane. My access to the front panel was limited, due to my lowly status and that the system ran a time-sharing system with many active users at the College and surrounding High Schools. All user interface devices were ASR-33, except for a local CRT terminal. Off-site access was dial-up at 300 baud on "conditioned" data lines. As far as I could determine, conditioning consisted of "red protected" covers on the bridging clips and terminal posts and a string tag. There were a couple of occasions where I was permitted to toggle in the Bootstrap Loader, which enabled input from the fanfold paper-tape reader. Then reading a program to read the operating system and system files from DECtape. If I recall useless information correctly, it was a PDP-8i Running TSS/8.21D. I mostly worked in BASIC, but the system offered FOCAL, FORTRAN and PAL-D. I did just enough in the other languages to be accepted by those who dwelled in them. All self-taught. I have taught a lot of computer classes, but have yet to take one. I am itching to build and play with the PiDP-8. It will be some time before my retired budget permits it. I picture rack mounting it next to my desk. I still have (I think) a portable TTY with thermal printer, with accoustic coupler for dial-up and either a DB-8 or a DB-25 for a little null-modem action. One day, I found myself explaining to a SWBT CO Foreman how I diagnosed their framing errors on T-Carrier from one End Office because I saw square root symbols (√√√√√√√√√) on the terminal screen instead of nulls (). Where did I get the Boolian algebra and the translation of ASCII to binary? Programming a PDP-8! For the benefit of those with the burning question, the Central Office was running Stratum 4 clock as a workaround for a temporary issue on a remote SLC-96. Asyncronicity between End Offices caused frequent resynchronization. A bit would fall off the end as a framing error. Science! I see some of you nodding your heads with understanding and other scratching their heads.

[@connomar55]

One of things I remember distinctly is having to learn a new alphabet. These things were hardwired using no solder, so the CPU, which was made up of hundreds of TTL Logic cards, plugged into sockets, and on the other side of the socket were all these interconnecting wires. I don't remember now which letters were left out in the row, column matrix, but it was all to prevent mixing up letters that were similar. Made fault finding that bit easier to have access to every input and output to the cards. The crazy thing was having circuit diagrams not only for the card but the backplane too. I spent many hours studying them to determine first, how it worked, then, why it didn't.

[@snorktorsk3434]

Toggle in the RIM loader to read the BIN loader from paper tape. We had one in college and used the tape reader from the recently-decommisioned DEUCE computer (roughly the size and shape of a washing machine on casters). We got a newer version with DECtape drives. Mostly worked in assembler but tried to use ALGOL from DECUS, but gave up on ALGOL when I found that it thought false AND true=false but true AND false=true. Loved that machine and went on to work with PDP-11 machines after college. DEC is sadly missed.

[@jimrobinton1901]

Very nice video - I used 2 of these linked together in the early 70's. The 8i was had those really nice switches (vs the 8e)....I think someone reversed the "deposit" key on ours, because I remember entering values and the just swiping across the top (hitting the reversed deposit key, and then clearing the switches all in one swipe). I moved a few years ago and finally through out my cooper colored "Introduction to Programming" book.... which I had kept it and given to someone like you !!

[@LJ45Chimera]

I've just made one of these. Great video. Learned a lot, Thanks

[@wa4aos]

Thanks for sharing these steps. Great video.

[@marcstevens9263]

Nice tutorial. It's clear and easy to understand. Thanks.

[@lukeanderson7168]

Just built Oscar's PiDP-8, this video was a super helpful intro, thanks!

[@ChrisMasto]

Glad it helped! Oscar’s kits are amazing.

[@user-tk2jy8xr8b]

Ideal for teaching machine codes and basics of how CPU works

[@cwilsonpa]

Nice Demo - The PDP-8 was the first computer that I worked with in University back in 1972. I just finished building a PiDP-8 kit I will try this program as soon as I place everything into the case. Thanks !

[@ChrisMasto]

Cool! Congratulations on your build. I still need to get around to re-doing the way I put mine in the box, I could do much better now at routing the external connectors.

[@axel1616]

Hi nice video. Fetch increment the program counter so the next instrucción to execute is ready when the next cycle fetch starts.

[@cookiekixx]

Thank you!

[@miken966]

I, also, think it's pretty cool.

[@kerryedavis]

I see the PDP-8 simulation still needs work. It should be showing you the Halt instruction in the Memory Buffer. Do you know if the guy has implemented the Word Count, Current Address, and Break indicators? Those were used during DMA data transfers such as disk drives.

[@americancitizen748]

Cool.

[@jukingeo]

So forgive my asking, but having being brought up in an age with computers having a keyboard and a screen, what can you do with a computer like this? Is it similar to a large version of a microcontroller and that it can control inputs and outputs?

[@ChrisMasto]

What I didn't show in the video is that you can connect to it with a terminal. I wasn't around for those days either, but I don't think people really spent their time toggling in programs to blink lights. You can run a lot of more sophisticated programs on even a small computer like this, including multi-user operating systems. The front panel stayed around for a while for bootstrapping and debugging, but went largely unused and then went away when it wasn't necessary to see the lights blinking to be sure that the computer was working. Like I said, this era was a little before my time, but it's interesting that you mention controlling inputs and outputs. My understanding is that the PDP/8 did end up getting used for a lot of industrial applications. There's one on display at the Computer History Museum in a rack of equipment used in brain surgery: www.computerhistory.org/revolution/minicomputers/11/331/1971

[@taavirei]

Is there any practical use for today you could apply it to?

[@ChrisMasto]

I think it would be a stretch of the word "practical" to come up with something. It's more for fun.

[@krielow08]

Amazing video and good info, but I can't help but get distracted by the angry gulping lol. What in the world did that beverage do to hurt you so much?

[@ChrisMasto]

I thought there was supposed to be big money in ASMR!

[@krielow08]

@@ChrisMasto =D

[@kerryedavis]

I've thought about getting one of these, but I can't stand the switches on the 8/I. Those on the 8/L, 8/E, etc, are much easier to use. The PiDP-8/e simulator has the right switches, but I hate the switchable-register setup of the 8/E, 8/F, 8/M... All the registers should be visible all the time, which the 8/I does - too bad about those awful switches - and the 8/L mostly does too.

[@kerryedavis]

@tradde11 Could do that with the 8/L too, just go across the top or the bottom for 1s or 0s. Or slap them, also easy. The worst part for me about the 8/i switches is that you push IN at the BOTTOM to make the TOP pop out for 1. Totally bass-ackwards. It makes more sense to LIFT a switch UP for 1. And you can more easily see their positions from a distance.

[@kerryedavis]

@tradde11 The 8/L used the same type of switches as the 8e, but it had all of the registers displaying on the front-panel at once, no selector switch. The 8/L didn't have the EAE option available, which made that a bit easier. The 8/L that I learned on was in High School and even with all the students using it, there was never a broken switch. The real champ for displaying all registers though is probably the PDP-12, with the -15 coming in a close second.

[@spit75d]

Kind of a built in logic analyzer 🤓

[@kargaroc386]

With only 8 instructions, the code for this system is probably slow, large-ish, and vaguely esoteric.

[@connomar55]

Kinda weird not hear all the fans running.

[@BoredInNW6]

Well, there's a Raspberry Pi in there, and the Pi 4 does run a little warm, so maybe some builds have one tiny fan...

[@jimjimsandburg2754]

@tradde11 12 bit words.

[@ChrisMasto]

@tradde11 If I could get my hands on one, I would be thrilled.

[@micheltrudeau5005]

$4

[@godsinbox]

I don't have an anecdote for this comment

[@ChrisMasto]

That reminds me of a time.