Brief History of PDP Computers | Hacker News Reader

Brief History of PDP Computers

entropicthoughts.com

47 pointsibobev27 comments

A lot of mistakes in this article, although it's well-intentioned.

There is a direct lineage from the PDP-1 to the PDP-4, and the 18-bit lineage ends with the PDP-15 (missing).

The dual-mode PDP-12 (PDP-8 + LINC) is missing from the 12-bit lineage.

The VAX (VAX-11 initially) was an offspring of the PDP-11 and the VAX-11 could natively run PDP-11 user-mode code. DEC then tried to use the VAX to unify both the 10 and 11 markets.

The PDP-11 and VAX software heritage lives on mostly in C and UNIX (NetBSD being the closest relative), and in VMS / NT. The PDP-10 heritage lives on mostly in Emacs.

"However, even its most powerful configuration wasn’t powerful enough to attract many pdp-10 users." They didn’t serve the same markets.

The PDP-10 was a time-sharing system that shone more for LISP than FORTRAN. For heavy number crunching and matmuls (the FORTRAN playground), 16-bit PDP-11s were usually used, with an auxiliary array processor such as the AP-120B or the CSPI MiniMAP. Those array processors could deliver more than 10 MFLOPS back then, when a minicomputer with a 50-100 KFLOPS FPU was already considered fast (FPUs were an expensive option back then).

Not very familiar with PDP history, but PDP-12 missing also caught my attention.

Regarding later heritage, to my understanding, several developers of the VMS kernel moved on to work on the Windows NT kernel. Whether it's really only coincidence that every letter of the acronym got shifted by one?

The first few versions of Windows NT had a very strong API resemblance with VMS, which is why Microsoft settled to pay to DEC a 9-digit $ amount, to avoid a legal battle. Though eventually that deal was less advantageous for DEC than it appeared from the amount of money, because it included the support of Windows NT for DEC computers.

The parts of the initial Windows NT API that did not resemble VMS looked liked cleaned-up versions of the UNIX API, e.g. the functions for handling file and device I/O.

The central role of asynchronous I/O in Windows NT was inherited from VMS, which in turn had inherited it from the RSX-11M operating system for PDP-11 computers (Dave Cutler had a major role in the development of all these 3 operating systems).

Whether VMS => WNT is a joke like IBM => HAL, is anyone's guess. A more certain thing is that IBM was named such as to be a hyperbolic substitute of the name of its main competitor, NCR (National => International, Cash Register => Business Machines)

The PDP-4 isn't binary compatible with the PDP-1. There is compatibility within the 4/7/9/15 line. So the PDP-1 stands out, and in that sense the lineage isn't direct.

Hi Lars!

Did AI or any other PDP-10s have a 340 display, and did LLOGO use that, or a raster framebuffer? What versions of LOGO does SIMH run, and is PDP-11 LOGO recovered and running?

I found a recently written Forth for the PDP-10 called "TENTH" (Ha ha! I suppose that means we should call Mitch Bradley's PDP-7 FORTH "SEVENTH"!), and I remember GREN (Ian Mackey) wrote his own PDP-10 FORTH on ITS as well as lots of other cool hacks in MIDAS. Do you know if anything from his home directory was recovered from backups?

https://github.com/aap/tenth

Hi Don!

The AI PDP-6 and 10 shared a Type 340 between them. It was the only 340 in the lab. Lick's Dynamic Modeling group had an LDS-1 from Evans&Sutherland.

LLOGO could display vector graphics on the 340 or GT40, and raster on the Knight TV or LOGO color TV (16 colors!)

LOGO versions on ITS include BBN LOGO for TOPS-10, CLOGO for ITS, LLOGO, 11LOGO, and Apple II LOGO. Yes, 11LOGO is recovered. There's an early standalone version, and a later version that ran on the SITS timesharing system on an 11/45.

Yes, there are GREN files. I have been in touch occasionally with Ian. Someone else called KLE wrote a FORTH in Maclisp.

Wow, awesome!

I appreciate, appropriated, and built on top of the excellent definitive SIMH Type 340 display work that you, Phil Budne, and Douglas Gwyn did, and I hope to incorporate your phosphor simulator with your permission and guidance! Imagine the beautiful trails that the Ultimate Hand will leave behind (direct manipulation power cycling via hand waving, implemented in Mitch's PDP-7 Forth):

https://hyperties.org/cabinet/ultimate-hand/

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

Please let Gren know I'd love to hear from him, it's been a long time since I last visited him in Santa Cruz.

Those LOGOs are a treasure trove! Thanks for digging them all up and bringing them back to life. I consider LLOGO (and the others) to be classic computer science literature worthy of study and analysis and emulation. LLOGO is especially interesting and challenging to emulate since it speaks so intimately with such a wide range of cool devices.

An authentic historic LOGO Turtle with an accurate 3D model and mechanical locomotion simulator that draws with SVG instead of ink would be a perfect portrait to paint!

The portrait: a 3D cabinet with live lights, a hot tube, and hands:

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

https://news.ycombinator.com/item?id=23054174

>DonHopkins on May 2, 2020 | parent | context | favorite | on: History of Logo

>Here is the source code to LLogo in MACLISP, which I stashed from the MIT-AI ITS system. It's a fascinating historical document, 12,480 lines of beautiful practical lisp code, defining where the rubber meets the road, with drivers for hardware like pots, plotters, robotic turtles, TV turtles, graphical displays, XGP laser printers, music devices, and lots of other interesting code and comments.

https://news.ycombinator.com/item?id=23054499

>larsbrinkhoff on May 2, 2020 [–]

>Also running on the emulator: PDP-10 Logo, PDP-11 Logo, Applle II Logo.

>The emulator doesn't support the robot arm yet.

Now the PDP-7 emulator supports fictional emulated devices like a Turing Machine co-processor, an Ultimate Machine hardware accelerated self-switcher-offer, and a Data Hand (webcam driven data glove without the glove).

Besides a PDP-6 emulator, PDP-10 emulator, PDP-11 emulator, and shared memory support to emulate AI's 10/11 interface, we also need a callable elevator emulator and a buzzable door lock emulator, since you recovered the chaosnet server to drive them!

https://github.com/PDP-10/its/blob/master/src/lmio1/door.1

The idea is that these device emulators can plug into all kinds of different machine emulators, just like the real Type 340 display can plug into a PDP-1, PDP-6, PDP-7, PDP-10.

Or even plugging an Englebart Mouse and Chord Keyset, Data Hand, Turing Machine, or Ultimate Machine device emulators into an Apple ][ emulator using $C0X0 memory mapped hardware registers and $CX00 PROM drivers instead of IOT instructions, so "IN#7" lets you type with a chord keyboard (driven by webcam hand tracking of course). I'm using and extending Paleotronic's excellent microM8 Apple ][ emulator written in Go that runs in WASM, and adding a Videx 80 column card emulator that my Forth terminal emulator needs:

https://github.com/SimHacker/WillWrightShowForFood/tree/main...

Mitch's PDP-7 Forth is the ideal way to integrate those fictional device emulators with the real Type 340 display device emulator in the PDP-7 emulator. And I'm reincarnating my Apple ][ Forth and terminal emulator, which I lost the source code to long ago, but still have a build on a floppy image, which can decompile and disassemble itself, to reverse engineer a rebuildable source code base.

Cabinet Manifesto:

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

Plugging devices into multiple machines:

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

The DataHand, layer by layer:

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

How a device reaches a machine:

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

Architecture and Lineage: Devices can travel farther than CPUs:

https://github.com/SimHacker/WillWrightShowForFood/blob/main...

More (old) Forth Stuff (mentioning my Apple ][ Forth system and terminal emulator I'm recovering):

https://donhopkins.com/home/catalog/lang/forth.html

>The first Forth system I used was Cap'n Software Forth, on the Apple ][, by John Draper. The first time I met John Draper was when Mike Grant brought him over to my house, because Mike's mother was fed up with Draper, and didn't want him staying over any longer. So Mike brought him over to stay at my house, instead. He had been attending some science fiction convention, was about to go to the Galopagos Islands, always insisted on doing back exercises with everyone, got very rude in an elevator when someone lit up a cigarette, and bragged he could smoke Mike's brother Greg under the table. In case you're ever at a party, and you have some pot that he wants to smoke and you just can't get rid of him, try filling up a bowl with some tobacco and offering it to him. It's a good idea to keep some "emergency tobacco" on your person at all times whenever attending raves in the bay area. My mom got fed up too, and ended up driving him all the way to the airport to get rid of him. On the way, he offered to sell us his extra can of peanuts, but my mom suggested that he might get hungry later, and that he had better hold onto them. What tact!

>I had a job programming Forth for a little company called "Computer Challenges", when I was in high school. I implemented my own Forth programming environment for the Apple ][ computer, and a graphics and animation package in 6502 assembly. Then I wrote an animated graphics demo with it, promoting Forth as a cross platform game programming language across Apple ][, C64, and BBC computers. (That was more than a few years before Java.)

Also the dual-mode LINC-8 which was the immediate PDP-12 predecessor. It was as much a PDP in all but the name.

    > it wasn’t called a computer then, because the word “computer” back then meant big mainframe systems that ran batch calculations

PDP being a minicomputer (at the time), it could do that too and cheaper. What I heard the reason for this was to circumvent procurement restrictions. The word "computer" meant a high level of scrutiny, but obviously a "Programmable Data Processor" isn't a computer because it doesn't have the word "computer" in it (duh). So just a sales / marketing trick.

The term "minicomputer" was first used in the marketing of PDP-8, but not immediately after its launch from 1965.

The use of "minicomputer" became widespread only in 1969, when it was explicitly derived from the word "miniskirt", which had become fashionable not long before that.

Quotation from "Electronic Design News", in July 1969:

“Design isn’t what it used to be. Today’s designer has available a ready-made solution to major problems — a minicomputer. Like the miniskirt, the small general-purpose computer presents the same basic commodity in a more appealing way.”

During the seventies, there was a classification of computers into mainframes like IBM System/370, supercomputers like Cray-1 and minicomputers like PDP-11.

Then in the second half of the seventies, "microcomputers" were added as the lowest tier.

That is quite the quote

Thanks for this bit of nostalgia. As a veteran user of DEC computers for most of my career, I really enjoyed this despite some of the omissions that others have pointed out. I could also add some additional thoughts to what else has also been mentioned, including LSI-11 which was a micro version of the PDP-ll. I really liked the orthogonal instruction set. My experience goes back to PDP-8 which were all over the place at Lawrence Livermore National Labs; they were using them basically as terminals for accessing the big CDC-7600/CDC-6600 supercomputer complex there. Some side points on operating systems such as RT-11 and peripherals such as RL01/RL02 might also have been interesting. But this was still a lovely bit of memorabilia, so thanks again! ;-) Oh, I almost forgot about the user group DECUS, a treasure trove of all kinds of goodies, including DECUS-C compiler which we used extensively. And of course MACRO-11 was our main workhorse for assembly language programming on the PDP-11 and LSI-11 for many years.

To round out the timeline I'd include the TX-0, first computer based on transistors, and essentially the experimental prototype/proof of concept of what became the PDP-1. https://en.wikipedia.org/wiki/TX-0

then on the other end of the timeline, the DECSYSTEM-20 which wasn't any longer called PDP but it was simply an upgraded PDP-10. https://en.wikipedia.org/wiki/DECSYSTEM-20

The DEC 20 I was familiar with was a PDP-10 with a PDP-11 as a frontend (i/o) processor. I recall one of the cookie messages was "Help I'm trapped in a PDP-11"

True enough, but I'll observe there's a lot of rounding out that could be done in various directions if one were so inclined.

I would have thought the vax owed more to the pdp-11 culture than the pdp-10. If you don’t want to move the line add a second one. Berkeley Unix really helped things network and hack and that came from the 11 onto the vax.

That's what I think too. The VAX is a lot more like the PDP-11 than the PDP-10. Hard core 36-bit PDP-10 programmers (like DIGEX, who I quoted in response to Walter's comment) were dismissive of and looked down on the 32 bit VAX.

Doug Humphrey's nickname was DIGEX, and he had a PDP-10 in his living room in Westchester Tower Apartments that he acquired from a loading dock at the University of Maryland. It was challenging to haul up in the elevator! It had two power cords, and two of us had to plug them in at the same time, into outlets on different circuits, so it got both hot legs.

He started one of the first ISPs by that name, which was later acquired by Worldcom:

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

The Digex Video! - Part 1:

https://www.youtube.com/watch?v=IsgROO4MIvc

DEF CON 12 - Doug Mohney, DIGEX At the Dawn of the Commercial Internet:

https://www.youtube.com/watch?v=uxMq-x9rlJM

The article also didn't mention the PDP-15, which was the fifth and last 18 bit DEC machine of the PDP-1 => 4 => 7 => 9 => 15 lineage.

That's right.

A lot of features of VAX and VMS are clearly inherited directly from PDP-11 and RSX-11M.

The main resemblances between VAX and PDP-10 are just that VAX is bigger and more powerful than PDP-11 and it is big enough and fast enough to be an upgrade even for PDP-10 not only from PDP-11.

Nonetheless there is something that VAX has inherited from PDP-10, but not really from the base DEC PDP-10 but from the enhancements that the users of PDP-10 had done to it.

The company BBN (Bolt Beranek and Newman Inc.) had made since 1970 a so-called "BBN Pager" for PDP-10, which was a hardware extension that added a paged memory management unit to PDP-10. They also designed the TENEX operating system for the PDP-10 extended with the BBN Pager.

The TENEX operating system is the origin of several very important innovations, like the memory-mapped files, which were later brought to UNIX by 4.2BSD, through SunOS 4.0 and 4.3BSD-Reno. Several of the earliest implementations of some Internet protocols, like Telnet and FTP, were done on computers running TENEX (i.e. extended PDP-10s). Implementing Telnet required the concept of pseudo-terminal, which was also imported in 4.2BSD and later the use of pseudo-terminals was expanded in various UNIX variants, to applications like terminal emulators in GUI desktops.

The paged memory management from which VAX got its name (Virtual Address Extension) comes directly from the BBN Pager extension of PDP-10.

I laughed (with suitable derision) when I saw the line from PDP-10 to VAX.

I learned how to program on a PDP-10. Lots of great memories.

"If you're not playing with 36 bits, you're not playing with a full DEC!" -Doug Humphrey (DIGEX) tormenting VAX weenies at DECUS

Same here. I still really like how symmetric the instruction set was.

From the MIT-AI Lab's file "AI:HUMOR;PDP-* LIST", the inimitable Mark Crispin weighs in on DEC's PDP's:

https://github.com/PDP-10/its-vault/blob/master/files/humor/...

  Date: Wednesday, 20 August 1986  03:42-EDT
  From: Mark Crispin <MRC%PANDA@SUMEX-AIM.ARPA>
  To:   TOPS-20@SU-SCORE.ARPA, Boken@RED.RUTGERS.EDU
  Re:   DEC's PDP's
  Postal-Address: 1802 Hackett Ave.; Mountain View, CA  94043-4431
  Phone: +1 (415) 968-1052

A number of people have requested my list of all the DEC PDP's, so I thought I'd bore you all with it.

The PDP-1 was an 18 bit machine. It was DEC's first computer, and some of the first timesharing systems were designed for it. It's also unique in being one's complement; all later DEC computers were two's complement. Some machines, such as one of MIT's PDP-1s, were in operation until the late '70s.

The PDP-2 was a designation reserved for a 24 bit machine, but as far as I can tell it was never even designed and definitely none were ever built.

The PDP-3 was a 36 bit machine that was designed but never built by DEC. However, Scientific Engineering Institute built one in 1960.

The PDP-4 was an 18 bit machine that was intended to be a cheaper, slower alternative to the PDP-1. It was so slow that it didn't sell well, although it was interesting for its auto-incrementing memory registers. It was not program-compatible with the PDP-1, but its instruction set was the basis of DEC's future 18 bit computers.

The PDP-5 was a 12 bit machine designed to be a small laboratory system. It used many of the ideas in the LINC (Laboratory Instruction Computer, designed by Lincoln Labs at MIT, some of which were built by DEC).

The PDP-6 was a 36 bit machine and the first machine to implement the most wonderful computer architecture known to man. It was rather expensive and difficult to maintain, and not many were sold. As a result, DEC cancelled 36 bit computers for what was to be the first of many times.

The PDP-7 was an 18 bit machine and the sucessor to the PDP-4. It was a major price/performance win over the PDP-4 and the first DEC computer to use wire-wrapping.

The PDP-8 was a 12 bit machine and the sucessor to the PDP-8. It basically defined the term "minicomputer", and went through several incarnations. The original PDP-8 was followed by the extremely slow PDP-8/S (as bad as the PDP-4 was to the PDP-1, but at least the /S was program-compatible). DEC recouped with the PDP-8/I (using MSI integrated circuits) and the smaller PDP-8/L, and somewhat later came out with the "Omnibus 8" machines -- the PDP-8/E, the PDP-8/F (a half-sized version of the PDP-8/E), the PDP-8/M (an OEM version of the PDP-8/F), and the final machine, the single board PDP-8/A. The PDP-8/A still exists after a fashion as a current DEC product.

The PDP-9 was an 18 bit machine and the sucessor to the PDP-7. It had a faster memory than the PDP-7 and was the first microprogrammed DEC computer. Modulo a 300 wire(!) ECO required in the first machines, the PDP-9 was a reliable machine and some are still in operation today. There was a short-lived PDP-9/L.

The PDP-10 was a 36 bit machine and the sucessor to the PDP-6. It is especially noted for its software, which represents the pinnacle of DEC software engineering and has never been equalled. The first KA10, largely installed in universities, created a whole generation of timesharing hackers. The follow-on KI10, with paging and using IC's instead of discrete components but otherwise unexciting, mostly was sold to commercial organizations. The KL10 went through several incarnations and is today the most representative of this marvelous machine. The KS10 was a small, low-speed (approximately KA10 performance) processor which was DEC's last successful implementation of this architecture.

The PDP-11 was a 16-bit machine that went through more implementations and operating systems than can be counted. Presently it superceded the less powerful PDP-8 as the representative minicomputer. While the PDP-11 used octal, it was in its deep heart of hearts a hexidecimal machine, and the first indicator of the creeping IBMification of DEC that took full fruit in the VAX. [I can hear the flames now...] Rather than fight it the customers loved it; more PDP-11's have been sold than any other DEC computer (possibly more than all the others combined).

The PDP-12 was a 12 bit machine and the sucessor to the PDP-8. It combined a LINC and a PDP-8 type processor in the same box and basically was a new model of the LINC-8 which was the same thing.

No PDP-13 was ever designed or built. Even DEC gets superstitious.

The PDP-14 was a 12 bit machine with a 1 bit register. It was used as a process control engine in applications that were felt to be too rugged for a PDP-8, and basically replaced a set of relays. Later DEC made PDP-8's suitable for this sort of thing, but it didn't stop them from the ultimate silliness of building a PDP-14 that used a PDP-8 as its console processor!

The PDP-15 was an 18 bit machine and the final one of this design built by DEC. More PDP-15's were built and sold than any of the others, and it went through several incarnations including some which used a PDP-11 as a front end. Apparently the cancellation of the PDP-15 came as a great surprise to the "Tiger Team" who worked on it, although considering its general ungainliness compared to comparable performance PDP-11's it wasn't surprising. In many ways the PDP-15 died for the same reason the PDP-10 did.

The PDP-16 was a "roll your own" 16 bit machine based on various "building blocks". Every PDP-16 was essentially custom-designed by the customer. It got a fair amount of attention when it was announced but evidentally didn't sell very well.

There was no PDP-17 or any other designator. DEC apparently decided that "PDP" had a perjorative ring to it.

----

Also from the humor directory, you might also enjoy singing along with "Alice's PDP-10":

https://github.com/PDP-10/its-vault/blob/master/files/humor/...

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DEC Mail from Ken Olsen to Gordon Bell, Dick Clayton, Jack Shields, and Jack Smith, 18 November 1980. A real memo. The 11/23 is the machine Crispin, above, says replaced the PDP-8, and Olsen has just had one delivered. Four dual boards, in a steel box, and he says the integrated circuits were a waste:

https://github.com/PDP-10/its-vault/blob/master/files/humor/...

The printer is the size of an IBM typewriter and arrived in a crate five feet tall that would not go through the doors of his house. The two RX02s fill about a third of their cabinet, and the rest is air. DEC made smaller floppies because the box was so big. He says anyone paying attention would have made the box fit the floppies. Every screw has its own washer and its own lock washer, and he lost one inside the machine. He wants the names: who designed it, who packaged it, who approved it for manufacturing, who approved it for field service. Bell had been saying the Japanese were coming on financing and manufacturing. Olsen says they are going to kill DEC by better design.

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