back to article Das blinkenlights are back thanks to RPi revival of the PDP-11

Always wanted a PDP-11, but don't have space for the iron? Good news: an obsolete computer enthusiast s offering beta tests of a kit designed to recreate the famous Digital Equipment Corporation box on a Raspberry Pi. As Obsolescence Guaranteed explained here earlier this month, “The PiDP-11 wants to bring back the experience …

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Devil

I cut my teeth on a PDP-11

back in the day, 11/34 at my high school, and 11/70 at the university. the 11/34 ran RT-11. The 11/70 ran RSTS/E. I did some interesting things with assembly language, the most useful of which was a re-write of the access program for diskettes [it was tee'd from a terminal on a 9600 baud serial port] that did NOT lose data. The one written by the grad student DID lose data, and was pretty much worthless with more than a handful of people on the system. students were supposed to do backups using that diskette drive, but write-only memory is pretty worthless.

WIthout my assembly language program, it was 'write only'. that's because the grad student made a n00b mistake: he assumed that the input buffer would never fill up. what I did to fix it: I sent one buffer's worth of data at a time, and polled for the next buffer after receiving it. Also mine had a FAT-like directory instead of skipping through the disk looking for "directory tags" that would fail for binary files. yeah, mine could store binary files, too. But it was generally incompatible with the 'grad student' BASIC version.

I gave the system operators the source and everything, gave copies to friends, etc. before I left. Thing is, I fear that it was generally unused because nobody understood it... [or they feared I'd put some kind of back door into it, but i thought it was pretty simple ya know? comments read like a book, too]

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Anonymous Coward

Re: I cut my teeth on a PDP-11

"Thing is, I fear that it was generally unused because nobody understood it..."

In my IT career I often took the time to automate tedious manual processes. Getting people to take the time to use the automation was a different matter.

One example was a BASIC program that merged code patches with the current release's compilation text. Even when there were patches over patches you could still read the final code flow. Which patch changed each location was clearly identified.

The system at that time was very heavily patched - but the official support team stuck to paper copies of the original listing. They often lost track of how overlaid patches were interacting.

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Re: I cut my teeth on a PDP-11

nooo nooo nooo. Did my thesis on a PDP11 (after spending a term or so walking into the Uni Mainframe to see the 'Hardware Fault' light illuminating the unused card punches.

Wow was that a revelation. I went from two lines of code a week to writing atom bomb simulations* (nothing to do with my thesis which was on fibre optic performance).

To be able to write code and not wait a 1/2 day or so for it to be run by the batch system was a fucking revelation. And now I can do it all again on a Pi. Must resist Must resist.

*source code deleted after converting from eV to tonnes TNT!

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Re: I cut my teeth on a PDP-11

Same here - my first was a PDP 11/05, that had been upgraded from 4KB to 8KB of core RAM. It had a high speed paper tape reader and high speed punch, as well as two, count 'em two, ASR-33 Teletype terminals.

It lived in the undergraduate room at the University where I studied in the mid to late 70's. You'd start up toggling in the paper tape bootstrap (14 sets of instructions from memory) and then read in the a tape to get it up and running properly - perhaps with the BASIC interpreter (multi user basic, what a buzz!). Writing assembler in the basic stream text editor, loading the (two pass) assembler, then link editing, loading a fresh tape at each step, and voila!

Ah, the memories!

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Re: I cut my teeth on a PDP-11

Let's not forget the joys of overlay swapping to squeeze the most out of that 64K. I eventually came up with some rather creative tricks that you might call "minimal root" where instead of common code being at the base overlay, there were multiple occurrences out on the ends of branches. This cured the "blob effect" where all the code used by more than one module migrated to the base and used up all the address space before you'd even loaded anything useful. It was also good for making all the init code disappear when no longer needed.

Of course we now have the Great Blob Object where all the "must have" features migrate up to the godlike object class from which all other object classes must descend. The only cure for that is carefully used multiple inheritance - but nobody knew how to use that safely.

Those who do not learn from history are doomed to repeat it.

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Holmes

Re: I cut my teeth on a PDP-11

bombastic bob wrote: I did some interesting things with assembly language

Real programmers have programmed in assembly at least once.

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Re: I cut my teeth on a PDP-11

Real programmers use inline assembler often, regardless of language.

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ds6
Coat

Re: I cut my teeth on a PDP-11

According to modern parlance, real programmers use JS.

And nothing but JS.

And get jobs for it.

I'm so very, very sorry.

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How noisy are the cooling fans?

Can't get into the proper zone to toggle front panel switches without cooling fans properly roaring away in the background^W^W my ears. Can I connect my line printer? Acoustically coupled modem? PC11? CR11? RK05? TU56?

More seriously, this might be an excellent teaching tool. IMNECTHO, DEC kit is the absolute pinnacle for ease of explaining and demonstrating computing concepts to students. Although, in today's world of DevOps App builders, understanding the basics no longer seems to be all that important. Sad that.

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Re: How noisy are the cooling fans?

”Although, in today's world of DevOps App builders, understanding the basics no longer seems to be all that important.“

Understanding the basics is still important, it’s just that the definition of ‘basic’ has changed through the years. Much like math or engineering students no longer learn the ‘basic’ skill of using a slide rule - because there’s just no point any more.

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Re: How noisy are the cooling fans?

The definition of basic might have changed in your eyes, but the heap and the stack still exist and knowing how to use them is just as important as it was 40 years ago. Unfortunately, I've interviewed new college graduate so-called programmers who don't even know they exist. Hell, I interviewed one poor kid who couldn't convert from hex to decimal to binary on paper, much less in his head. Worse, he didn't understand why that kind of "skill" might be handy ... in his words "Why should I know that? That's what the computer is for!".

As for your example, I use sliderules almost every day. Here's my favorite. Now THAT's what I call a Sun Workstation!

Why? Because a slipstick's more accurate and faster than guestimating for fencing, fertilizer, seed, irrigation, roofing, paint, roadbase, DG, working loads on beams and the like, and a lot easier than firing up a computer. Just to really make you think, I also use an abacus nearly daily. It's in the feed barn. I use it to calculate livestock feed & supplement needs. Electric calculators tend to die in a matter of weeks in that kind of environment.

Horses for courses and all that ...

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Anonymous Coward

Re: How noisy are the cooling fans?

IT "basics" also includes a knowledge of electronics and radio. Most of my colleagues had no idea of how a computer and its associated electronics worked. Therefore they could not double-guess when underlying constraints in the technology might be responsible for intermittent errors in the system.

Even something as simple as the speed of propagation of electromagnetic waves through various media was a mystery to them.

I even had an official "network designer" once ask me about speeds - "What does 'mega' mean?".

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Re: Basic skill of slide rule

I used to teach remedial maths to biology undergrads. Nearly all of them had been taught that logs were historic and related to the time before calculators, and they weren't that happy to hear that they were fundamental to science. One day, one of my mature students, who understood the maths back to front but nevertheless dutifully turned up to even the maths tutorials, asked if we'd like to see his slide rule. "I'm an old fossil" he explained apologetically.

By the end of the hour the three students still struggling with the concept of logs had got it absolutely solid. The "old fossil" gave me the slide rule and I used it for years: some people massively benefit from a degree of "physical learning." I think the same must be true for computing and projects like this are invaluable.

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Re: Basic skill of slide rule

The other advantage of slide-rules was that it was 'necessary' to approx. the order of magnitude answer - which was good brain training.

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Re: How noisy are the cooling fans? @Jake

My slipstick is a Faber Castell log-log slide rule. I would like to say that it is the same one that was bought for me in 1971 when I went to senior school, but that got lost in one of many house moves, and I had to do a like-for-like replacement from eBay.

Although I think I still know how to use all of the scales (it's got around 20 different ones), I don't do the type of maths that it's best suited for very often.

I have one of my Grandfather's slide rules, probably dating back to the 1930's that he would have used at the RAE in Farnborough (it was one of the UKs primary aircraft research institutions). It's engraved polished ivory on wooden slides, but feels so fragile that I don't play with it very much.

When it comes to abacuses, not me. I used a blackboard and chalk and counting gates when counting sheep and hay bales on my father-in-law's farm before he retired.

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Re: How noisy are the cooling fans?

"Much like math or engineering students no longer learn the ‘basic’ skill of using a slide rule - because there’s just no point any more."

No point? Hardly.

Keep in mind that batteries die, power grids go down, but slide rules need neither.

Mine got me through a Physics exam when my HP-45 batteries died back in my undergrad days.

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Re: How noisy are the cooling fans?

So you work in both farming and computing industries? That's a first for me!

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Re: How noisy are the cooling fans?

Waseem, it actually makes perfect sense. When you think about it, farming is a form of computing ... analog computing, perhaps, but computing nonetheless.

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Re: How noisy are the cooling fans?

"...batteries die, power grids go down, but slide rules need neither."

I keep meaning to put my slide rule and tables of logarithmic and trigonometric functions into a little glassed-in case, with a small hammer and sign reading "break glass in case of power failure".

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Anonymous Coward

Re: How noisy are the cooling fans?

"[...] work in both farming and computing industries? That's a first for me!"

Back in the late 1960s many programmers were young women. When they wanted to start a family it would previously have been expected that they would leave work for many years.

ICL's Hilary Cropper decided that she could employ them as part-time home programmers - now that Teletype devices on interactive services were starting to be available. So began the era of "Hilary's Pregnant Programmers".

There was at least one guy who joined that crew. He left full time programming to do dairy farming in Wales. He complained that a local manual exchange operator would sometimes disconnect his Teletype connection when she checked on the long-distance call's conversation - "because the line was making funny noises".

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Re: How noisy are the cooling fans?

About 30 years ago, my daughter subtitled my CRC handbook "Post Apocalypse Science Rebuild Notes" and insisted on shelving it next to the Firefox books, the UBC, and various other bits & bobs :-)

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Re: How noisy are the cooling fans?

That's the Foxfire books, of course. Obvious brain fart is obvious. Mea culpa.

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Stop

Re: How noisy are the cooling fans?

STOP. DO NOT PASS GO.

El Reg, we need to know more about this programming group. There's a great story in there, I'm sure.

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Re: How noisy are the cooling fans?

So you work in both farming and computing industries? That's a first for me!

Cue old joke: Why are experts like farmers? They're both people out standing in their fields...

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Re: How noisy are the cooling fans?

Slide rulers & log tables...

Having both and knowing how to use them should be mandatory - they still work when there’s no power or internet.

Not sure if that’s why the VMS admin (yes, still a thing!) ad my old workplace had a 6’ slide rule in his office marked up with a label “Emergency backup CPU”, but it’ll still be usable long after everything else is landfill

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Re: How noisy are the cooling fans?

Back in the late 1960s many programmers were young women. When they wanted to start a family it would previously have been expected that they would leave work for many years.

Early 60s as well. My mother was one of them. And yes, when she started a family (her first-born was someone who might just post here as Steve the Cynic), she left work, the 60s being what they were.

But she reached the level of Chief Programmer at LEO.

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Re: Basic skill of slide rule

The "old fossil" gave me the slide rule and I used it for years

This made me think of the best slide rule I ever saw. Cue: 1977. I'm about to start secondary school, and it's the end of the previous academic year (last at primary school). They sent us to the Comprehensive down the road for a tour, and hanging on the wall in one of the maths classrooms was a slide rule.

"Hanging on the wall"? Sure. It was six feet long, for teaching slide rule technique.

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Happy

Re: Basic skill of slide rule

"Hanging on the wall"? Sure. It was six feet long, for teaching slide rule technique."

A local restaurant (one of those that specializes in having kitschy decor with antiques, etc. everywhere) has one of these on the wall. It spans 2 or 3 booths. I doubt many of the younger crowd even knows what it is when dining there. They also have a WWII-era Army Jeep on the wall sideways. I'm always a bit afraid to sit under it..

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Can't wait

I've built two of the PDP-8 kits and had great fun with them.

I'll be ordering a couple of the kits as soon as Oscar opens the ordering.

Why? Well, I worked for Dec from 1979 to 1999. I have a MicroVax in my Garage so a PDP-11 would make the set. Same that the new one does not have a UniBus. I have an old prototype interface that I'd love to get working.

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Re: Can't wait

I had a working MicroVax (model 3100-80 with two SCSI hard drives) for quite a while in the early 2000s, even using it as a web server with NetBSD running on it. Then I acquired a PDP-11 from the same place - both had been standbys for when similar machines had been installed at client sites for warehouse automation. Never did get the PDP working, so I sold it. When the guy came to collect it he took one look inside and pointed out that the card I had assumed was the RAM was in fact some kind of controller board. Doh.

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Pint

Completely pointless

Well done everyone, beers all around!

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Anonymous Coward

Re: Completely pointless

I tell you, this post has been far from pointless—I now have an urge to buy a slide rule and touch up on my knowledge of heap logistics.

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an obsolete computer enthusiast

I say, that's a bit harsh...

Can't you just call him retired?

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Anonymous Coward

Re: an obsolete computer enthusiast

A rather unfortunate turn of phrase methinks.

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Go

Re: an obsolete computer enthusiast

That must be an oxymoron.

If the computer has an enthusiast, it is not an obsolete device.

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Re: an obsolete computer enthusiast

"Self unemployed" is my preferred moniker.

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My first job after leaving the company I did a sandwich course with still used PDP-11, I think an 11/70 and an 11/73 to run stock and order processing systems for a group of steel processing companies. We still had to run backups onto reels of mag tape. After about a year, we started to migrate to MicroVAX, and, having the least experience with the PDPs , I was tasked to convert the processing software over from the PDP version to VAX/VMS. Happy days (1990 ish)

I don't know what happened to the PDPs, but I was almost scared to touch them with their open cabinets and huge pcbs visible. Very noisy as well.

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All this talk about BASIC and not one mention of FOCAL. Back in my PDP-8 days at university, BASIC was a pain because it was too big to fit into the 4k word memory and so it was split into two parts, I'm assuming the parser and the runtime, that had to be loaded separately from paper tape. FOCAL, on the other hand, was half the size and so you could easily load it in one go and get some coursework done in your allocated 1 hour slot.

But about this PDP-11 emulator, unless it comes with Adventure then I'm not interested.

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Happy

PDP-11 Adventure

I'm sure the fortran source is out there somewhere...

So, what did PLUGGH do then?

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Re: PDP-11 Adventure

I'm sure the fortran source is out there somewhere...

In many forms:

http://rickadams.org/adventure/e_downloads.html

https://www.dwheeler.com/adventure/

are just two I have bookmarked.

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@Thoguht

I once loaded up the 8K BASIC interpreter on our 12K PDP-8/E (slowly, as we only had the tape reader on an ASR33) hoping that it would allow me to get round some of the limitations of 8K FOCAL. No such luck. The BASIC was almost identical to FOCAL in functionality - they just swapped the commands over and made it much less efficient!

Phil.

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Pint

Adventure

"But about this PDP-11 emulator, unless it comes with Adventure then I'm not interested."

The local university had an 11/40, an 11/70, and a VAX as I recall. I remember playing Zork I on it when I was perhaps 9 or 10 years old, using both a VT-100 terminal and a Decwriter. (Was Zork I part of the Adventure series at the time?) Long story as to why I even got to be in the lab. Somewhere I may even have one of the printouts on 140-column green bar paper from one of those sessions. As I recall, it was written in FORTRAN to run on the 11/70. (or it may have been the 11/40, I don't remember)

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Happy, happy days...

Happy days. We had an 11/34A at school, running RSTS/E (can't remember the version) - my first ever commercial product (written with another EE at the same university) was a BASIC+ Decompiler.- very popular product,=.

I loved RSTS/E, RT-11, RSX-11,... I still have a J11 chip on on "Shelf of Doom", along with my Sinclair Scientific calculator (still works), my British Thornton slide rule and a set of PDP-8 manuals (among much other detritus).

Somewhere in the loft is an AXP-433 workstation running Windows 2000...

(ex. DECUS Europe OpenVMS Chairman, ex-DEC employee in France, UK & Switzerland).

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“The PiDP-11 wants to bring back the experience of PDP-11 Blinkenlights, with its pretty 1970s Magenta/Red colour scheme.”

That magenta; it's going to get them into trouble with T-Mobile.

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Nah.

Prior art.

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Painful

Many years ago in a house share we had a PDP-11 and WinchesterDisk stacked on the landing, by the bathroom.

It is very painful to collide with these devices when trying to get to the toilet in the dark. I still have a dent in my kneecap...

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TRT
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A thing of beauty...

is a joy forever.

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Oh wow! I read a little bit about this project but had assumed it was a one off - it did seem an amazing amount of effort so I guess I shouldn't be surprised that it's now available as a kit. Would definitely like to build one of these, as the PDP-11 had a wonderfully elegant instruction set.

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Anonymous Coward

wonderfully elegant instruction set. (@james_smith)

"the PDP-11 had a wonderfully elegant instruction set."

Programmers Cards were a Thing back in the day. Here's one DEC prepared earlier:

https://archive.org/details/bitsavers_decpdp11PDul75_1582192

or direct to theappropriate PDF at

https://archive.org/download/bitsavers_decpdp11PDul75_1582192/PDP-11_Programming_Card_Jul75_text.pdf

Also available via Bitsavers (and/or archive.org) are DEC (and other) Processor Handbooks and such other outdated stuff (e.g. diagnostics) as are generally considered irrelevant in the 'modern' world. Bitsavers is a great resource for such things, though for DEC stuff there are often other places to look.

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Brings back memories...

Of my first 'real' job in IT. It was on the Isle of Man working for a small company that did systems software ('C' compilers, assemblers etc). They had a PDP 11/23 and an 11/34 running RSX11 (? - it's been 30 years...). They had the PDPs to develop and test cross-compilers so you could code on a PDP11 and compile for a new-fangled 68K processor, for example. 'C' compiler used was Whitesmiths...

Happy days...

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