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A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

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Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#31

Post by mrandish »

rswail wrote: post #29
mrandish wrote: post #26

Earlier quoted context omitted.

The influence was what the people who learned computing in the 70s on PDP-11s at university, went on to do with what they'd learned in the 80s. Also, the 6809 shipped in 1978. Little known fact, the Macintosh was going to be based on the 6809 and Jef Raskin's team had 6809 Mac prototypes running before Steve got Motorola to drop their price on the 68000 (in part because Moto was panicked over losing out on the PC).

Agreed, just saying that the PDPs were where a lot of the people developing micro computers cut their teeth eg CP/M looks a lot like RT-11. Minicomputers like the PDP-11 begat microcomputers around 8080s, Z80s, 6509s, 6502s. "Home" microcomputers started around 1977/78 with the Apple ][ and TRS-80 and PET.

For sure, by volume the impact of the PDP-11 was almost entirely through micros and workstations because they were taking over so fast. Although, Unix and C did spread like wildfire from the PDP-11 to other minis. In fact, C was originally created for porting Unix.

In terms of timing, the PDP-11 shipped in early 1970 and was an immediate best-seller. Back then, students didn't get much hands-on computer time until their final two years so by the mid-70s its influence was already being felt. The 6809 was being designed in 1975 and the architecture was clearly inspired by the PDP-11's orthogonal ISA, interrupts stack handling, etc.

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#32

Post by phire »

kens wrote: post #10
themafia wrote: post #7

Earlier quoted context omitted.

The Internet (mostly), the C language, the Unix Operating System were all developed and deployed on PDPs. The BASIC language /and/ an 8080 emulator was developed on a PDP in order to deploy to the Altair. I would argue that Intel was so highly influenced by Datapoint due to sheer proximity and early inexperience in the field.

I don't think you can count PDP-10 things (Internet, BASIC, 8080 emulator) to support the influence of the PDP-11, since they were completely different computers. The PDP-10 was a 36-bit mainframe, while the PDP-11 was a 16-bit minicomputer.

PDP's lack of naming really confuses things, they essentially just numbered the computers by release date.

There are like 3-5 completely different family trees of computers in their numbering scheme (depending on how you count), all of them are notable in some way.

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#33

Post by cesaref »

phire wrote: post #32
kens wrote: post #10

Earlier quoted context omitted.

I don't think you can count PDP-10 things (Internet, BASIC, 8080 emulator) to support the influence of the PDP-11, since they were completely different computers. The PDP-10 was a 36-bit mainframe, while the PDP-11 was a 16-bit minicomputer.

PDP's lack of naming really confuses things, they essentially just numbered the computers by release date. There are like 3-5 completely different family trees of computers in their numbering scheme (depending on how you count), all of them are notable in some way.

Yeah, there were two busses, and the bigger ones were certainly rather impressive. I built a PDP-11/23 out of spare bits gifted from a university physics department in the late 80s, and it was awesome, but nothing like an 11/70 or anything like that!

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#34

Post by mrandish »

nickcw wrote: post #28

I'm not old enough to have used a PDP-11 so I read through the assembly code description with interest. Wow, it seems so modern. I've used a lot of assembly languages over the years but I'd feel immediately at home here. Nice sensible orthogonal instruction set with enough registers and a stack pointer. It reminded me immediately of ARM assembly - what a breath of fresh air that was when it came it. I never realised…

My first computer had a 6809 with 4K of RAM and I learned assembler on that 6809, which was greatly inspired by the PDP-11 architecture. My second computer was an Amiga 1000 with a 68000, a CPU even more directly a successor to the PDP-11 than any other. As far as I knew, those two PDP-11-like systems were computer architecture. Orthogonal instruction sets, user and system stacks treated just like any other register, layered interrupts, indirect addressing, memory mapped I/O, auto-increment/decrement, relocatable zero page, contiguous flat memory map, relative addressing that made position-independent, re-entrant code trivially easy. Yeah, in the 1980s, I led a sheltered, happy computing life.

It was around the mid-90s by the time I tried x86 assembler. I don't think "shocked" quite captures the experience. It was more like disbelief, then something akin to abject horror, which finally just faded into creeping existential dread. Before the X86, I loved coding in assembler but the nicest thing I can say about x86, is it motivated me to learn C as fast as possible. :-)

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#37

Post by ubermonkey »

There's a concept in history whose name escapes me, but which was evoked often when Harrison Tyler died in 2025. Tyler was a private citizen, but he was of note because he was the grandson of the US's 10th president John Tyler -- who died in 1862.

The gist is how surprising bridges to the past are closer than you realize -- as is the past itself.

At my first corporate job in 1994, we had a machine room. Those weren't uncommon back then. What WAS uncommon was that, over in a corner, sandwiched between racks of shiny new DEC Alphas, was a PDP-11 that was still running production code.

My employer then was TeleCheck, which did point of sale risk analysis for checks. The business had originally been run as independent state-by-state franchises, and back then someone had the bright idea to create an IT company that provided services to these franchisees -- and, occasionally, to other companies, too. By the time I was hired, the franchises AND the IT company had all been brought under one ownership, and all the IT company's external clients had gone elsewhere EXCEPT ONE.

That holdout was perfectly happy with what they got from that ancient computer.

I assume it eventually died, but TeleCheck had a DEEP bench of DEC talent, so it could've kept running a long, long time.

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#38

Post by JKCalhoun »

Obsolescence Guaranteed makes a PDP-11 replica [1]. At the heart is a Raspberry Pi running emulation software. All switches, LEDs are physical—all wrapped up in a clever case that looks like the original.

I have bought a couple of their kits and can vouch for the quality of them.

[1] https://obsolescence.dev/pdp11.html

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#39

Post by jakzurr »

Used several of these at school in the 90's. IIRC intro classes used VAX/VMS (was the machine called VAX-1170?). But all the higher undergrad classes used Unix on PDP-11/70's, like in the picture. Of course, I hardly ever saw one up close. :p

Re: A brief tour of the PDP-11, the most influential minicomputer of all time (2022)

#40

Post by le-mark »

ErroneousBosh wrote: post #15
amirhirsch wrote: post #13

Earlier quoted context omitted.

014747 makes me smile I built the PDP-11/70 emulator that controls the nuclear reactors in Ontario. That was 20 years ago and I'm probably still the youngest person who can read PDP-11 assembly (and the raw octal)

There's a decent chance you're younger than me, but I can still read it. Coincidentally about 20 years ago I got asked to fix a bug in some PDP11 code that ran on real hardware because it was tripping up an emulated system. Nothing wrong with the emulator as such, it was just a logic bug in the program that they no longer wanted to work around. I made the fateful mistake of saying "Sure, sounds fun, how hard could it…

Not pdp-11 but once I was tasked with fixing a c program the offshore team had failed to fix for over a year. I basically took a month off (at my desk) after I fixed it the first day. They were happy, I was a legend at that company!
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