A brief tour of the PDP-11, the most influential minicomputer of all time
'The history of computing could arguably be divided into three eras: that of mainframes, minicomputers, and microcomputers. Minicomputers provided an important bridge between the first mainframes and the ubiquitous micros of today. This is the story of the PDP-11, the most influential and successful minicomputer ever. In their moment, minicomputers were used in a variety of applications. They served as communications controllers, instrument controllers, large system pre-processors, desk calculators, and real-time data acquisition handlers. But they also laid the foundation for significant hardware architecture advances and contributed greatly to modern operating systems, programming languages, and interactive computing as we know them today. In today’s world of computing, in which every computer runs some variant of Windows, Mac, or Linux, it’s hard to distinguish between the CPUs underneath the operating system. But there was a time when differences in CPU architecture were a big deal. The PDP-11 helps explain why that was the case. The PDP-11 was introduced in 1970, a time when most computing was done on expensive GE, CDC, and IBM mainframes that few people had access to. There were no laptops, desktops, or personal computers. Programming was done by only a few companies, mostly in assembly, COBOL, and FORTRAN. Input was done on punched cards, and programs ran in non-interactive batch runs.' -- source: https://arstechnica.com/gadgets/2022/03/a-brief-tour-of-the-pdp-11-the-most-... Cheers, Peter -- Peter Reutemann Dept. of Computer Science University of Waikato, NZ +64 (7) 858-5174 (office) +64 (7) 577-5304 (home office) https://www.cs.waikato.ac.nz/~fracpete/ http://www.data-mining.co.nz/
On Tue, 15 Mar 2022 11:45:44 +1300, Peter Reutemann quoted:
'The PDP-11 was introduced in 1970 ...'
The first computer I was actually able to touch and run code on was a PDP-11/34 at Waikato Uni in 1979. It was running a “cafeteria system” where you put your program (written in Waterloo Fortran, “WATFOR”) on mark-sense cards (punch cards where you put black marks instead of making holes), then stood in line to feed your deck through the reader, then wait for the printer to print your program listing (including compiler syntax errors) and (if you were lucky) output. The main University system was a PDP-11/70 running RSTS/E, which was an interactive timesharing system. The following year, they got their first VAX. The PDP-11 is known as the birthplace of Unix in (approximately) its production form. Though a prototype was previously put together on an old PDP-7, which was a machine with a very different architecture, with an 18-bit word and no hardware stack. This guy has done a brief overview of the major DEC PDP lines <https://www.youtube.com/watch?v=bQUeMyAMQwo>, ending by putting together a “PiDP-11” PDP-11 emulator built around a Raspberry π. The PDP-10 was also an interesting family of machines, very much in the “mainframe” class at the time. These were used to develop two influential operating systems of the 1970s: TENEX from BBN and ITS (“Incompatible Timesharing System”) from the MIT AI Lab.
On Tue, 15 Mar 2022 11:45:44 +1300, Peter Reutemann wrote:
https://arstechnica.com/gadgets/2022/03/a-brief-tour-of-the-pdp-11-the-most-...
Spot the mistake: MOV $65536, R0 / The highest value in 16 bits Also from my memory, this (note I prefer writing things in lowercase, not uppercase) begin: movb (r0)+, (r1)+ dec r2 bne begin (3 instructions, 6 bytes) can be shortened to begin: movb (r0)+, (r1)+ sob r2, begin (2 instructions, 4 bytes). It’s been a while since I had anything to do with PDP-11 assembly language. It could be that the very earliest models had no “sob” instruction, this was added later.
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Peter Reutemann