Talk:PDP-11

Instruction set orthogonality

The stuff about orthogonal addressing modes is not completely correct. I think the writer is confusing with the VAX which was (almost?) completely orthogonal. The PDP-11 was not. Most instructions were two address, with one operand (usually the source) allowing all addressing modes, but the other operand had to be a register. The MOV instruction allowed all modes for both operands. There were also some single operand instructions, some no-operand instructions, and a few weirdos that didn't fit the pattern. In all, it was a cleaner than a monstrosity like Intel 8088, but you couldn't call it completely orthogonal. (I don't think i ever wrote any PDP-11 assembler, but i recently translated some into ANSI C. I've also done minor tweaks to an emulator.)

I'm sorry, but you're incorrect. With exception of the floating point stuff and the fact that ADD and SUB must be word-oriented (and not byte-oriented), all of the two-operand PDP-11 opcodes are orthogonal, taking the general form of:

(Byte_Flag) (3-bit_opcode) (6-bit_Source_Specifier) (6-bit_Destination_Specifier)

And both specifiers took precisely the same form:

(3-bit_Mode) (3-bit_Register_Selector)

The supported opcodes were:

• x1 MOV
• x2 CMP
• x3 BIT
• x4 BIC
• x5 BIS
• 06 ADD (only on 16-bit word)
• 16 SUB (only on 16-bit word)

The (rather limited) Floating Instruction Set, by comparison, implements a stack-oriented machine that always has one of its operands on the R6 stack. And the Floating Point Processor instruction set is, as you say, non-orthogonal, generally having one operand specified by generalized specifier and one operand that must be in a Floating Register. But please realize that both of these were options to the basic PDP-11 instruction set and were designed to fit into the rather-small opcode space allowed by the 16-bit wordlength. (As mentioned in the Orthogonal instruction set article, a fully-orthogonal instruction set isn't very bit-efficient.)

Atlant 13:48, 22 Mar 2005 (UTC)

Things get somewhat less orthogonal with the opcodes added later on, like MUL and XOR; those take a register plus a general operand. Paul Koning 20:00, 17 March 2007 (UTC)

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Is that the index addressing mode, which uses an index word following the instruction word, can only be applied to only one operand? enjoy

No, it could be applied to either operand. Guy Harris 01:34, 16 March 2006 (UTC)

Not just either, but both operands. Constructs such as MOV 2(R2),4(R3) were entirely valid, and would assemble (in octal) as 016263; 000002; 000004 Xarqi 11:53, 2 October 2007 (UTC)

FIS has both operands on a stack, and delivers the result on the same stack. The register operand just denotes which register holds the stack pointer. There is a different instruction set extension EIS, which is implemented in all processors since the 11/40, which fits the above description of non-orthogonality. EIS contains fixed point multiplication and divison, and arithmetic shift. The register operand of MUL and DIV instructions is a set of 2 registers, if the register is an even numbered one. --Glasreiniger 08:12, 16 March 2006 (UTC)

Cleanup?

PDP-11 was flagged as needing attention because "this needs to be more easily understood".

Though it is a bit dry, I had no trouble understanding the article. Its terms appear to be well-defined.

What parts must be more easily understood??

[207.112.115.248]

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If you are an assembly language programmer, it is perfectly clear. But most folks are not.

I think PDP-11 needs two more sections:

• On the social significance of the machine. Who used it? What did they do with it? What new feats did it enable? What was its market niche?

• Why did DEC build it? (The article almost answers this.) Why did they drop it? Is it associated with struggles within DEC? Did it make money for DEC? (Those of us who were fondly dependent on one or more DEC machines are deeply interested in this sort of thing.)

[207.172.11.147]

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The section "Decline of the PDP-11" asserts a design deficiency that eventually made the model uncompetitive. The second, parenthesized, paragraph gives details of a programming project (too detailed for this location, I think) for the purpose of providing a counterexample. I'm too new here to delete someone else's contribution, but the solution seems to be for the statement in the first paragraph to be less categorical. --Spike, Brentwood NH

—Preceding unsigned comment added by 24.60.78.79 (talk) 15:33, 18 October 2008 (UTC)

Hearing no objection, (!) I'll tackle this today. --Spike-from-NH (talk) 19:14, 27 October 2008 (UTC)

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I've finished sprucing up architectural details of the PDP-11 and PDP-8. I found text in the present and past tense; my guess is that the present is used for implementation facts (which would still be true if you were to locate a machine) and the past is used for conventions and implications on programmers (who presumably are mostly in the past). Not sure this guess is correct, nor that my additions are totally consistent. --Spike, Brentwood NH

PDP-11 application areas

I am aware that the PDP-11 had the following types of applications in the 1980's:

• Academic institutions used them to train scientists and engineers in computer programming. The PDP-11 had a great little Fortran compiler and could service multiple terminals in a computer lab.
• They got used as remote communications processors to control printers etc. connected to mainframe computers.
• Siemens used duplicated-redundant PDP-11's to operate their telex exchanges.

I suspect that they also got a lot of use in industry as numerical machine or industrial process controllers. Basically the PC became more powerful and cheaper for the single user and industrial applications and the VAX was the natural upgrade path before computer servers came along. kiwiinapanic 10:19 Jan 20, 2003 (UTC)

That's a tiny fraction of the applications. Here are some more:

• General timesharing (e.g., RSTS/E, IAS
• Process control systems
• Embedded controllers
• Turnkey applications (e.g., Typeset-11)
• Commercial data processing systems (CTS-300, CTS-500)

and so on. Paul Koning 20:00, 17 March 2007 (UTC)

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I agree that it could use the sections suggested above (significance, and why it died). Alas, I don't have time to add them now - I just used my quota fixing the technical content! I'll add a bit about the second, though.

As to the technical content, a couple of fixes: the devices really did put an address on the bus (at least on the Unibus, haven't checked my Q-bus manuals); manuals show the interrupt vector being gated onto lines D02 through D08. The Unibus was a real bus, not just a backplane (old-timers will remember those long flat white Unibus cables), and although I don't recall using them for the Q-bus (perhaps for analog reasons), the Qbus really was a bus, not just a backplane. There were also 4 interrupt levels, BR4 through BR7; there was also the DMA-only NPR (you could do DMA on BR levels, but I don't know of any devices that did).

Sorry about all the extra RETURNs, and the numerous versions to fix them; I can't break the automatic habit of typing RETURN when I get near the end of a line!

Noel 16:06, 2 Mar 2004 (UTC)

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I added information on interrupts (and many other things), but today checked my PDP-11 Reference Card, which lists no device that used BR7. Was about to "correct" the article, until reading your comment. Was there a BR7/BG7? Did any device use it?

--Spike-from-NH (talk) 20:38, 26 October 2008 (UTC)

Physical packaging

The article contains the following text:

Finally, the PDP-11 was designed to be produced in a factory by semiskilled labor. All of the dimensions of its pieces were relatively noncritical. All parts of the computer chassis were constructed from injection-molded plastic, or bent steel rod (lighter than sheet metal). It used a push-bonded backplane. That is, the printed circuit board plugged into a backplane connector. The backplane connector had terminals that could be connected by pushing wires into them. The terminal would cut the insulation around the wire and bite into the wire to for a gas-tight (i.e. corrosion-proof, therefore reliable) connection. The connector blocks were very similar to telephone connection blocks. The case was injection-molded plastic that snapped over the steel-rod chassis.

Does anyone have any idea what that paragraph is trying to talk about? It clearly contains a few things that are true; some '11s did use a bent-wire frame, many '11s used automatic wire-wrapping for some portion of their backplane wiring, etc., but the paragraph as a whole seems to have a fairly loose grip on reality, and certainly doesn't reflect the original PDP-11 implementation.

If no one chimes in, I'll eventually take a crack at cleaning it up, but the whole topic will be somewhat lengthy as a number of radically different packaging technologies were used by the various PDP-11 models.

Atlant 17:15, 8 Feb 2005 (UTC)

Digital sold UNIX for the PDP-11?

Can anyone verify that Digital sold UNIX for the PDP-11? I'm tempted to move UNIX to the third-party section.

--Rochkind 8 July 2005 04:41 (UTC)

I don't think Digital resold Unix directly, but Unix was absolutely available for the PDP-11; this was Thompson and Ritchie's second platform after the PDP-7. (See the picture at the top of this article!) DEC's "Telco" product Line (TPG) was essentially devoted to the Unix business. By the time of Ultrix on the VAX, Digital was directly reselling Unix.

Atlant 8 July 2005 12:49 (UTC)

To put it more precisely: At the time of Ultrix-32 they also sold Ultrix-11 for the PDP-11. Ultrix-11 was essentially BSD-2.9 IIRC. See PUPS archive at http://minnie.tuhs.org/PUPS/ --Glasreiniger 07:29, 11 July 2005 (UTC)

Thanks for the info! --Rochkind 18:29, 15 July 2005 (UTC)

Iskra Delta 800: Clandestine clone or not?

I started collecting information about historical computers and creating related articles. So I stumbled upon Iskra Delta 800, which is said to be PDP-11/34 compatible with some extensions, developed by Iskra Delta but using actual J11.

Iskra Delta was a company from Yugoslavia, which was not behind the "iron curtain". I do not recall making completely unlicensed clones (like behind the curtain), although it is quite possible that using original components one would make a compatible computer (the components themselves were not copied). Peripheral devices were often not produced at all and originals were used. Read about that just a tad bit more in History of computer hardware in the SFRY.

Does anyone have more information on this or can provide some guidance? My searches for PDP 11 "compatibles" yielded no results other than Iskra Delta 800 - was it really the only official non-clandestine one?

--Aleksandar Šušnjar 15:21, 14 April 2006 (UTC)

As far as I know Digital never licensed the PDP-11 to anyone, so all clones are clandestine. Paul Koning 20:00, 17 March 2007 (UTC)

PDP-11's Influence on the Design of C

At the top of the article, it is mentioned that the PDP-11's instruction set influenced the design of C. However, I do not see any evidence to support this claim given in the article. Could someone who knows what these alleged connections are possibly add a section about them?

Done! -- RoySmith (talk) 22:08, 26 June 2006 (UTC)

You're mistaken[1]. --StuartBrady 22:59, 26 June 2006 (UTC)

Thanks for the correction. -- RoySmith (talk) 23:57, 26 June 2006 (UTC)

Thanks. It's been reverted, though!

Just to clarify: the ++ and -- operators were a feature of B (C's predecessor), which was developed on the PDP-7. Dennis Ritchie himself says this (see under "More History") on the page that I linked to above. --StuartBrady 11:59, 30 June 2006 (UTC)

There are several possibilities. Of course, it is not the ++ and -- operators, which are suspect to be inspired from the PDP11, but the idiom of using the autoincrement/decrement modes for pointers like *p++ and *--p (and to avoid the syntactically valid *p-- and *++p). Probably more characteristic is the omission of single precision floating point numbers in C. This was due to the fact, that the whole machine has to be switched between single and double (via PSW flag). --Glasreiniger 12:36, 30 June 2006 (UTC)

The point about *p++ is nonsense. C has "float" and "double". --StuartBrady (Talk) 13:00, 30 June 2006 (UTC)

Cool down, please. C has float, but only for storing single precision. In V6 C, FP operations are done in double, always. --Glasreiniger 19:27, 30 June 2006 (UTC)

I'm quite calm. As far as I can tell, that simply not true anymore. --StuartBrady (Talk) 21:31, 30 June 2006 (UTC)

It's not true anymore, but the PDP-11 isn't the primarily platform for C anymore, either. :-) It was true at the time that the PDP-11 was the primary platform, and the PDP-11 might have influenced that aspect of C. The ANSI C standard was developed at a time when PDP-11's were no longer the primary platform for C, so the standards folk might have decided it was time to allow float arithmetic to be done in single precision. (My copy of the standard is at home, so I don't have it handy, but I can check whether the Rationale discusses that.) Guy Harris 22:30, 30 June 2006 (UTC)

Right. :-) I was reading section 6.3.1.8 in C99, and it appears that the implementation is still free to do arithmetic in double precision.

It doesn't seem fair to say that the PDP-11's instruction set has any influence on modern C (which is currently implied)... and I don't think the instruction set's influence on early implementations is especially noteworthy, as all implementations of C are influenced by whatever architecture(s) they run on. --StuartBrady (Talk) 23:11, 30 June 2006 (UTC)

I just looked at my pdp 11/45 processor handbook; the 11/45 at least, had float and double versions of most of the floating point instructions. There were some of the earlier machines that had a less sophisticated FPU; it's possible they had a PSW mode bit to switch precisions, but the 11/45 certainly didn't. -- RoySmith (talk) 23:56, 30 June 2006 (UTC)

So what did the SETF and SETD instructions do? Guy Harris 01:25, 1 July 2006 (UTC)

Sigh. I should have read the book more carefully. SETF and SETD do indeed set/clear a bit in the FPP status register (not the PSW). This bit then determines whether FP math is done single or double. -- RoySmith (talk) 02:24, 1 July 2006 (UTC)

IMHO it is self-evident that any modern C development is not influenced by the PDP-11. Nobody has implied this. But in the early development phase, the embryonic state of C, the PDP-11 was the most influent of the machines used for C and Unix development. Another point, where the PDP-11 heritage is clearly visible, is the rule that only 3 register declarations were effective in a function body. IRC these were the PDP-11 R2,R3,R4, as R0,R1 were reserved for scratch, R5 for global addressing, and R6, R7 for stack and programcounter. Nowadays register declarations are faily useless. --Glasreiniger 18:00, 3 July 2006 (UTC)

I'll apologize here for reverting StuartBrady's note regarding this. I did not see the reference, was working quickly, and should not have reverted. I was wrong, he was right, and I apologize. -- Gnetwerker 19:27, 10 July 2006 (UTC)

This discussion resolved the issue incorrectly. Quoting Dennis Ritchie from http://cm.bell-labs.com/cm/cs/who/dmr/chist.html:

"People often guess that they were created to use the auto-increment and auto-decrement address modes provided by the DEC PDP-11 on which C and Unix first became popular. This is historically impossible, since there was no PDP-11 when B was developed."

"Even the alleged similarity between PDP-11 assembly and C is apparently "a folk myth, pure and simple, which continues propagating because its a handy sound bite, not because there is any truth to it whatsoever."

Any other conclusion not supported by citation not only contradicts the creator of C, but also constitutes original research.

However, since the folk myth is so widespread, it would be appropriate for the article to specifically say that it is a folk myth, rather than go through a predictably infinite process of revert/unrevert.

Still, the main point is that Dennis Ritchie says that C was not influenced by the PDP-11 assembly, which contradicts what the article has been saying since July. Dougmerritt 3:48, 19 December 2006

Let me cite from Ritchie:

Second, although the original PDP-11 did not provide for floating-point arithmetic, the manufacturer promised that it would soon be available. Floating-point operations had been added to BCPL in our Multics and GCOS compilers by defining special operators, but the mechanism was possible only because on the relevant machines, a single word was large enough to contain a floating-point number; this was not true on the 16-bit PDP-11.

Finally, the B and BCPL model implied overhead in dealing with pointers: the language rules, by defining a pointer as an index in an array of words, forced pointers to be represented as word indices. Each pointer reference generated a run-time scale conversion from the pointer to the byte address expected by the hardware.

For all these reasons, it seemed that a typing scheme was necessary to cope with characters and byte addressing, and to prepare for the coming floating-point hardware. Other issues, particularly type safety and interface checking, did not seem as important then as they became later.

This looks pretty much like a manifest influence from PDP-11 to some C developments. —The preceding unsigned comment was added by Glasreiniger (talk • contribs) 10:04, 5 January 2007 (UTC).

Well, not exactly, at least not as previously claimed. Carefully reading the quote you provided, it seems clear that Ritchie is saying that consideration of several issues lead to C being typed, rather than untyped as was BCPL. Yes, the issues in question were hardware related, but note that none of that is what the main article was saying. The latter was indeed a folk myth. If you are saying that you would like to add to the main article a note saying that C became a typed language due to consideration of PDP 11 architectural issues, that seems potentially supported by the above quote (but is a different issue, at least in its particulars, than previously discussed).

What fits and does not fit in a machine word has been historically important in many contexts, e.g. the fact that "two (18-bit) machine addresses fit in one (36-bit) machine word" had a very, very important influence on Lisp, much more centrally important than the historical accident that lead to the infamous names "car" and cdr". Similarly here with C: it would have been literally unfeasibly inefficient to ignore the issue that the target architecture had byte-oriented pointers and that high precision floating point required two machine words rather than one -- true enough, but rather different than the usual claims about C increment/decrement etc. being derived from the PDP 11 instruction set (which, as mentioned at top of page, previously appeared in B on the PDP 7). Dougmerritt 04:17, 23 January 2007 (UTC)

Ritchie's article directly contradicts the "myth" of the increment/decrement operators. It does not address the "myth" about float vs. double. It may be that the "myth" is in fact true, or it may be false, but a different citation would be needed to settle that. For what it's worth, the PDP-11 floating point processor supports both types, but it requires a mode switch instruction to select the one or the other. Paul Koning 21:42, 5 September 2007 (UTC)

"Last Remaining" PDP-11

An anon inserted a claim that an Australian transit system was the "last remaining" PDP-11 installation. I know personally that there are many PDP-11s in process-control systems that are still in service, but this is OR, as was the original insertion. I have edited it to simply state that the system in question is still in service (though this is unsourced) rather than remove it. Feel free to provide cites, revert, whatever. -- Gnetwerker 17:22, 5 October 2006 (UTC)

The section mentions something called "Swedish PASCAL". Being Swedish, I can't help wondering what this is. Is that some variant of PASCAL that's not widely known, or is it just some editor that confused Sweden and Switzerland? (which would not be very rare) —The preceding unsigned comment was added by 83.248.152.18 (talk • contribs) 15:48, 11 October 2006 (UTC).

It's "the first public domain Pascal compiler for the DEC PDP11/70 minicomputer", according to http://www.uni-koeln.de/~al001/basp5.html. Given that its author's name was Seved Torstendahl, according to http://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/decus/11s007.html, I suspect the "Swedish" refers to the nationality of the author.

(Google is your friend.) Guy Harris 23:20, 11 October 2006 (UTC)

I added some "citation needed" tags -- this isn't meant as a black mark, just a note to all of us here that we need to try to find some sources. I think the additions are, in general, good. -- Gnetwerker 23:45, 17 November 2006 (UTC)

"No dedicated I/O bus" is inaccurate

That statement is true for a few of the early models, like the 11/20. It is not true for the later, higher performance, models, starting with the 11/45 and much more obviously so for the 11/70. In the 11/70 there are two I/O buses (Unibus and Massbus), plus a memory bus.

That said, it is true for all of them that there are no dedicated I/O instructions and the I/O devices are memory-mapped. The same is true in many other processor architectures, whether they have a unified bus or not. Paul Koning 20:00, 17 March 2007 (UTC)

PDP-11s still in service?

Per previous editors comments I'm removied the following section from the article. I'd love to know if any of these stories are true, but they need verification to be in the article.--agr 15:28, 8 July 2007 (UTC)

The computer system in the METROL metropolitan train control centre in Melbourne, Australia is still in regular commercial service. This system runs an operating system coded in Swedish PASCAL for the creation of train timetables, fleet management and passenger information displays. Several nuclear plants around the world, including Canada, the Netherlands and Sweden, still run PDP-11s. Many research institutions still regularly run PDP-11s for data collection or instrumentation control. Australia Post still use PDP-11/93's running RSX-11 on some of their older Optical Character Recognition machinery. Flight simulators (such as the 747 operated by MK Airlines) use a PDP-11. Computer Organization and Programming course at the Technion is still being taught using PDP-11 Assembly.

for the last one, see #2 at http://webcourse.cs.technion.ac.il/234118/Spring2007/en/syllabus.html also see the literature and FAQ sections for further proof

The last PDP11/44 running in Canada (confirmed 2007 by HP) was stopped July 2009. Réjean Fournier Rio Tinto Alcan coordinator. We still have others models in process control.

A PDP-11/23 runs the cyclotron in the University of Washington's nuclear medicine lab as of 2011. I've seen it with my own eyes.

PDP-11 Self-Propagating Instruction

I have fond memories of the PDP-11. As a consequence of the architecture, the instruction set contained as a valid instruction, "MOV -(PC),-(PC)". When encountered, this instruction propagated itself backwards through the machine's memory, all the way to Address 0. Sometimes, this complicated debugging, since the offending code could be wiped out. On the other hand, it made a handy memory diagnostic. You toggled an "012727" into the highest location in memory, and hit "Run". If there was a serious memory failure, you could find it by toggling in various addresses to examine, and seeing how far down the "012727's" had propagated.

Alan Hochberg 19:17, 12 July 2007 (UTC)hochbeam

It's 014747, but apart from that, yes indeed, that was a neat trick. Paul Koning 21:44, 5 September 2007 (UTC)

Difference between EMT and TRAP?

So the one is called "trap", and the other "emulator trap". What is the actual difference here? Also, how do these traps work? The 68k will take a value from the trap you specify and stick it into the PC to that the cpu effectively enters an error handling routine. Does the PDP-11 do a similar thing? Wilsonsamm (talk) 10:44, 15 February 2008 (UTC)

It uses the same stack mechanism as interrupts - which was a feature that the 69k imitated. Tedickey (talk) 12:00, 15 February 2008 (UTC)

From a hardware point of view, there was no difference between TRAP and EMT. But the software typically used them for different purposes.

Atlant (talk) 13:14, 15 February 2008 (UTC)

There is one difference: they trigger different vectors. If I recall correctly, there is also a very small obscure difference: something like the priority of interrupts taken if several pending interrupts are present differs between the two instructions. —EncMstr 17:07, 15 February 2008 (UTC)

Yes, of course the vectors vary. And I'm sorry, but I don't have my microcode listings handy so I can't say whether there is a definite "interrupt priority" between the two. (I wonder if I still have my 11/34A and 11/23/24 microcode listings...)

Atlant (talk) 17:44, 15 February 2008 (UTC)

The notion of "priority" doesn't really apply here. They are exceptions, not interrupts, in the sense that some other computer architectures make the distinction. Or "synchronous traps" vs. "asynchronous traps/interrupts". Any one instruction can only be an EMT or a TRAP, not both, so there isn't any priority. Indeed, the hardware difference is that they go to different vectors (EMT to 030, TRAP to 034). What happens then is up to software. The low byte is ignored by the hardware. Software typically uses it as a request code; it picks up the saved PC, subtracts 2, and reads that word (that's the instruction) to get the low byte. Paul Koning (talk) 22:46, 15 February 2008 (UTC)

Yeah, it was a priority thing, but not that kind. It was that either EMT or TRAP, but not the other, would execute the instruction first, then field any pending interrupt. Or maybe it was the order of the trap status word flag was altered? Whatever it was, it almost never mattered what the distinction was in a real application. 22:52, 15 February 2008 (UTC) —Preceding unsigned comment added by EncMstr (talk • contribs)

Trap status word flag -- that's the trace trap. Are you thinking about the distinction between the RTI and RTT instructions? They are the same except for the treatment of the T bit. Paul Koning (talk) 22:55, 17 February 2008 (UTC)

What? EMT and TRAP trigger different vectors? I was under the impression that you could specify the vector to use by doing EMT 277 or TRAP 277. Now when the CPU encounters these traps, what actually happens? does it simply pop R7 onto -(R6) before moving the word in (say) o277 into R7? —Preceding unsigned comment added by 86.144.16.111 (talk) 17:03, 20 March 2008 (UTC)

No, the trap vectors for each kind of trap or interrupt were fixed (by a combination of hardware and microcode). But the low byte of the TRAP and EMT instructions wasn't interpreted by the hardware so by referencing -2(SP) the TRAP- or EMT-servicing routine could read the opcode that invoked the TRAP or EMT. It could then dispatch ("case") based on the low-byte of that opcode. Typically, IIRC, the operating system used the EMT instructions and TRAP was available to the user.

(Note that the access to the opcode was more-complex when memory management was in use as it usually had to refer back to the processor mode that was in effect when the TRAP or EMT was executed, not the processor mode of the TRAP- or EMT-servicing routine.)

Atlant (talk) 17:13, 20 March 2008 (UTC)

Macro-11 article

I just reverted a merge with MACRO-11 for two reasons: (1) I think merges should be proposed first, (2) in this particular case, merging a programming language with a hardware article isn't necessarily a good idea.

Admittedly the MACRO-11 article is short, but that could be cured by expanding it.

Paul Koning (talk) 23:02, 17 February 2008 (UTC)

My main concern with the MACRO-11 article is that it is not notable enough to carry its own article; it has no application or context outside of its use in PDP-11 systems, especially since both are defunct and only of historical interest. The alternative that I will pursue is deletion. I also don't see how or why PDP-11 should be a hardware article. First, it already contains an assembly programming section which I expanded to merge the MACRO-11 content. Secondly, the PDP-11 refers to a system, not exclusively the hardware, which would be a different article, PDP-11 hardware. To put it another way, a discussion of TiVo includes both the hardware and software -- and there is no separate article to discuss its software. If MACRO-11 were independent of the PDP-11, I would agree that it would warrant its own article; as it is, however, MACRO-11 is merely a sub-topic of the PDP-11, and as you admit, it doesn't contain enough content to justify a split on organizational grounds. Ham Pastrami (talk) 00:08, 18 February 2008 (UTC)

Ah, not to mention the list of operating systems, which is also not hardware. Ham Pastrami (talk) 00:11, 18 February 2008 (UTC)

I don't agree with the "notable" argument, especially since Macro-11 clearly serves as the template for many other assembly languages. Apart from that, I still don't understand why that justifies skipping the normal process -- discuss first, act after there is time to see that there is consensus. Paul Koning (talk) 15:26, 18 February 2008 (UTC)

I also do not agree with the "notable argument"!--Tim32 (talk) 01:06, 8 May 2008 (UTC)

Me either. The Tivo analogy is wildly off point: Tivo is an appliance, inseparable from its built-in software. That's not the case with a general-purpose computer. Now if there was a separate article on the PDP-11 instruction set, I would agree that that material belongs here. But a macro assembly language is far, far more than a representation of the computer's instruction set. Jeh (talk) 07:25, 8 May 2008 (UTC)

It really bugs me that the merge of "MACRO-11" was done again, even after I pointed out that there is a process to follow for this (which wasn't followed) and after there were several objections and no one speaking up in favor. Why was this done? Paul Koning (talk) 21:28, 19 May 2008 (UTC)

I'd just like to comment that IMHO, the native assembly language of one of the most influential architectures in computer history should be notable enough for Wikipedia. Also, from experience of reading and editing similar articles, I would expect an article entitled "PDP-11" to focus mainly on the hardware, with in-depth descriptions of associated operating systems, assembly languages etc. to be delegated to other articles. Letdorf (talk) 09:48, 20 May 2008 (UTC).

So, revert the merge. The merge obviously flies in the face of consensus. It wouldn't hurt to flesh out the Macro-11 article with more information about directives, lexical operators, etc. Jeh (talk) 14:22, 21 May 2008 (UTC)

I have done the deed. I think one way to avoid similar future well-meaning mistakes would be to expand and change the "Macro-11" section here into "available programming languages." Jeh (talk) 00:59, 22 May 2008 (UTC)

That paper tape picture

This picture, while a very nicely done picture, suggests that the PDP-11 was stuck in the Stone Age. The picture of the old PDP-11 with DECtape drives doesn't help either. In fact, later models of the PDP-11 worked with a wide variety of MASSBUS peripherals including RP06 disk drives. Does anyone have some pictures of such? Jeh (talk) 01:02, 22 May 2008 (UTC)

A picture of newer/larger peripherals, or perhaps a picture of a large 11/70 system, would certainly be nice. Then again, the existing pictures are also appropriate, reflecting the first few years of the product line. Paul Koning (talk) 16:47, 21 August 2008 (UTC)

Time span

The article says that DEC sold the PDP-11 in the 70s and 80s. I think that is slightly misleading. The last PDP-11 model from DEC, the PDP-11/93 and PDP-11/94 were introduced in 1990. Note that this was a new model. That would imply that they still had a fairly acceptable business into the 90s as well. /bqt (bqt@softjar.se) --213.65.173.92 (talk) 12:43, 26 July 2008 (UTC)

Maybe, but everyone was more focused on VAXes, SPARCstations, high end PCs, etc. by then. Even though I was a PDP nut, I didn't pay any attention to the 90 series, and it was barely mentioned at DECus meetings. —EncMstr (talk) 16:21, 26 July 2008 (UTC)

If reliable references can be supplied, I think this should be mentioned. Stating that DEC was selling the PDP-11 in the 70s and 80s when in fact sales continued through to the 90s makes the statement inaccurate. Rilak (talk) 06:57, 27 July 2008 (UTC)

Reliable references? The 11/93 and 11/94 was introduced in 1990 (anyone have any marketing material? Otherwise, how about the manuals for the new machines, dated 1990, and marked as new material, which are available at bitsavers?). What more do you need? I don't really know what kind of references are acceptable, and available. This is as close to a known fact as anything I can think of. What references do we have that the PDP-11 started selling in 1970? Anyway, DEC then sold the (almost) whole PDP-11 software business to Mentec in 1994. In 1998 DEC made available firmware upgrades for the 11/93 and 11/94 to cope with a Y2K issue (I have the upgrade on my systems, and it have a copyright notice saying 1998). Mentec continued to sell new PDP-11 systems will into the 21st century. In fact, there is still atleast one company making new PDP-11 processors. /bqt (bqt@softjar.se) 212.112.174.86 (talk) 08:54, 20 August 2008 (UTC)

I was not questioning the truthfulness of your edits, I'm just saying that any statement or claim needs to be referenced (it is standard Wikipedia policy). Go ahead, edit the article to make it more complete. I have found a reliable reference here: [2] (bottom of page) quote: "May 1990: The 20th anniversary of the first PDP-11 computer is marked by the introduction of two new PDP-11 systems: the MicroPDP-11/93 and the PDP-11/94." Rilak (talk) 11:45, 20 August 2008 (UTC)

:) I didn't think you were questioning the truthfulness as such. I just asked about the need for references. After all, the original claim of the PDP-11 being sold in the 70s and 80s didn't have any references either. It's just that it feels like the need for references sometimes seems excessive. And especially when it comes to some information while other information that appears to be on the same level are provided without references. Where should the line be drawn? It feels a little arbitrary, and perhaps wrong at times. /bqt (bqt@softjar.se) --212.112.174.86 (talk) 17:44, 23 September 2008 (UTC)

The reason why I said it needs references when adding such facts is more important as most editors will find that a computer sold in the 70s and 80s was still around in the 90s to be highly dubious, and therefore there is a risk it will be removed. Adding references stops that from happening. Rilak (talk) 08:56, 24 September 2008 (UTC)

Who makes new PDP-11 processors? There are lots of people in the classic computer crowd who'd like to know. We've been trying to contact Mentec about PDP-11 things to no avail. Frotz (talk) 01:35, 21 August 2008 (UTC)

I don't know how much "advertisement" is okay. But right now, the last manufacturer of PDP-11 processors that you can stick in your old backplane are Quickware (that I know of). And then of course you also have different levels of emulation, from Strobe who makes some hardware to pure software implementations. (bqt@softjar.se) --212.112.174.86 (talk) 17:44, 23 September 2008 (UTC)

Use of term "virtual address space" for 64k addresses

Applied to the 128k (and higher), it's easy to see. But applying it to the 64k address space requires some better explanation than "no", as expressed by User:Jeh Tedickey (talk) 11:22, 16 September 2008 (UTC)

Can anyone explain this comment to me? :) (bqt@softjar.se) --212.112.174.86 (talk) 17:44, 23 September 2008 (UTC)

Well I did write more than "no" in the summary, but on later read the summary says nothing the text didn't. My bad.

Sure... First, "physical address space" always means the actual, directly-addressable RAM addresses, after translation, mapping, whatever—the bits that go out on the memory bus. Now when memory mapping is turned on, the 64K worth of addresses that can be asserted by a running program, the addresses that appear in the 16-bit Program Counter or Stack Pointer register or any register used for deferred addressing, pointers stored in memory, etc., are before translation or mapping. Therefore we can't call those physical addresses. So we need a different word for them.

It's true that the PDP-11 architecture handbook doesn't use the term "virtual" there. But "virtual" is what we always called the pre-translation addresses in the PDP-11 forums around DECUS. In fact it was a point of some amusement that the machine's virtual address space was smaller than the typical installed RAM, the opposite of the (much better) situation on the VAX.

I frankly don't remember what the official name was, and it's possible DEC didn't come up with one. I have emailed the question to a PDP-11 expert and amateur computer archivist; he should know.

I'm thinking that the term "logical address space" might be better here, though, as it doesn't imply the possibility of paging (as "virtual" does)...and of course the PDP-11 did not have paging, i.e., there was no concept of a virtual or logical address being mapped to a page not currently resident in RAM.

The separate I & D space feature of course gives you two 64K virtual, or logical, address spaces, one for instruction references and one for data. The MMU automatically selects the "I map" or the "D map" depending on where the address came from: If from the PC, that's of course the I map; if the SP, the D map; I don't remember the other rules.

One other point: I removed the comment about 8 KB I/O space because that encroaches upon the physical address space, not the virtual (or logical). A program running with mapping enabled on a PDP-11 really can see a full 64KB (wow! a whole 64K?! :) ) linear address space that is mapped to 64K of RAM. (Or 64K I space plus 64K D space, on processors capable of that.) There's no need for the I/O space to be mapped into your task's address space as long as you rely on the O/S and drivers to do your I/O for you.

I hope all this helps; if not, please ask further.

So... shall we change it from "virtual" to "logical"? Jeh (talk) 19:14, 23 September 2008 (UTC)

Looks like the answer is "virtual" after all! My memory was flawed. My friend replied with this quote from the doc:

"When the PDP-11/45 Memory Management Unit is operating, the normal

16 bit direct byte address is no longer interpreted as a direct Physical Address (PA) but as a Virtual Address (VA) containing information to be used in constructing a new 18-bit physical address. The information contained in the Virtual Address (VA) is combined with relocation information contained in the Page Address Register (PAR) (see 6.4) to yield an 18-bit Physical Address (PA)."

That's from the PDP-11/45 Processor Handbook (1975), chapter 6, "Memory Management", section 6.2, "Virtual Addressing". Later PDP-11's of course supported up to 22-bit physical addresses. So there you have it. Jeh (talk) 05:39, 24 September 2008 (UTC)

That's more/less what I pointed out first (for 128Kb configurations, it's virtual). But the base configuration had 64k addressing, 56Kb memory. (Most of the PDP-11's I used had only that - or less). Tedickey (talk) 15:41, 24 September 2008 (UTC)

But even on a system without separate I & D space (or without that feature enabled) you can have your 64K virtual mapped to an assortment of 8K pages somewhere in a larger physical space - assuming the system supported more than 16 bits of physical address space, of course. If the 11's you worked on had 64K or less RAM they may have been 16 bit physical. Jeh (talk) 16:01, 24 September 2008 (UTC)

yes - most of them were 16-bit physical addresses, e.g., running RT-11 Tedickey (talk) 16:08, 24 September 2008 (UTC)

And to just make one point clear here. The PDP-11 could very well support a demand paged system (which is a different topic than virtual memory). The MMU have pages, and you can have pages that are invalid, and which causes a trap to the OS when referred to. And the OS can then change the mapping information for that page and restart the instruction. Hmm, maybe a clarification of the difference between virtual memory and demand paging should be written (or maybe one exists, I haven't checked). Lots of people seem to confuse the two nowadays. But I don't think that topic strictly belongs in an article about the PDP-11. However, several PDP-11 operating systems supported the use of virtual memory, but none ever implemented demand paging (as far as I know). The hardware could however do it. /bqt@softjar.se --212.112.174.86 (talk) 16:42, 30 September 2008 (UTC)

Splitting off architectural details

Following the example of the article on the Atmel AVR, I have split off former Section 5, Architectural details, into a separate article PDP-11 architecture. This section was about half of the total PDP-11 article, which had gotten big, and would be of exclusive interest to techies, while the remaining text is of interest to persons studying the PDP-11 as a phenomenon.

The only changes I've made during this pass is that I didn't think the various optional instruction-set packages deserved separate mention in the Table of Contents; they are all now in Section 3.7, Optional instruction sets. I've changed capitalization in some of the section heads to be more like Wikipedia, and created links between the two articles. For now, I won't delete any of the See Alsos; other editors who know the works pointed to may decide they belong in one article and not the other. --Spike-from-NH (talk) 00:16, 15 February 2009 (UTC)

Afterthought: I've also moved the entire section on "PDP-11 lore" to PDP-11 architecture as well. It belongs there (if it belongs anywhere!) as it denies a "folk myth" on the impact of the instruction architecture. The section on MACRO-11 might deserve the same thing, but I'll wait to see if there is buy-in or outrage at this surgery. --Spike-from-NH (talk) 00:37, 15 February 2009 (UTC)

In fact, there has been no comment at all, so the section on MACRO-11 is now moved. --Spike-from-NH (talk) 22:04, 27 August 2009 (UTC)

Memory-size timeframe

The term "common" doesn't appear to fit, since multiple-megabytes for a minicomputer were arguably rare in the late 1970s when the VAX was introduced. Suggest that the comment be toned down to reflect that Tedickey (talk) 21:00, 25 August 2009 (UTC)

A comparable assertion (which doesn't assert that megabytes were "common") is made in the first paragraph of Section 3, "The Decline of the PDP-11." A separate problem with the sentence in the intro is that it asserts a fatal problem with the PDP-11, but instead of explaining it, directs the reader through the link "64k barrier" to the 16-bit article, which nowhere explains the problem or the "barrier," or relates 64k to 16-bit addressing except at the end,in examples involving the Intel architecture. I recommend you simply delete the sentence. --Spike-from-NH (talk) 04:12, 27 August 2009 (UTC)

The basic design of the PDP-11 was sound

A recent addition in the 'Decline' section was 'The basic design of the PDP-11 was sound, except for its 16 bit logical address space' (addition is underlined). While this contributed to its decline in the late 1980's, I would say that making it have 16 bit logical addresses was a quite reasonable decision for circa 1970. Memory was expensive and the PDP-11 was always meant to be an affordable machine. In fact, a larger logical address would probably have required further expensive hardware to implement and would not fit well into 16 bit general purpose registers and would not fit well in the instruction format. Thoughts?  Stepho  talk  05:14, 7 June 2011 (UTC)

I took it out, it's at least a little ungracious criticism of a design that lasted for (a couple of decades...hey, there's no HISTORY in the article. When was the first PDP 11 sold? When was the last one sold? How many were sold?). If you want to criticize a short-sighted design, someone should write the article "Blunders in the design of the IBM PC" - if only IBM's team had known they were going to sell more than 10 or 20 thousand of the beasts... --Wtshymanski (talk) 14:17, 7 June 2011 (UTC)

It's depressing to do a Google search for "Digital Equipment Corporation history PDP-11" and have the *second* hit be the Wikipedia entry you just updated 3 mintues before...--Wtshymanski (talk) 14:34, 7 June 2011 (UTC)

(actually I usually find my Wikipedia entry is the number one result. Not depressing but scary to me!) W Nowicki (talk)

It wasn't a sound design, even in 1970. Memory was selling for around $1000/kilobyte then and dropping fairly fast. Affordability has nothing to do with it. Putting $64,000 worth of memory in a minicomputer based system was not unheard of and Unibus was designed from the beginning for 18-bit addresses (256KB). Designing something that would max out in a couple of years was a foreseeably bad decision. As for longevity, the PDP-11 came out in 1970; The Motorola 68000 in late 1979. By then no one in their right mind was designing new systems around the PDP-11. I had several arguments with DEC people about this in the 70s, including one with Gordon Bell. They were all hardware people and their argument was that any software bigger than 64K should be segmented. Later on VAXen were sold, and priced, as midrange systems, and that kept DEC alive for another decade, until PCs got powerful enough to compete. If the PDP-11 had been designed with a larger address space, we'd probably still be using them. Saying "the basic design of the PDP-11 was sound" is pure POV, and if we can't agree on wording, it shouldn't be in the article.--agr (talk) 15:02, 7 June 2011 (UTC)

Depends on if you're a comp sci weenie or running a business, I guess. They sold 170,000 of them in 10 years - that was a *lot* for those days. The comany went from a few thousand employees to 100,000. They made a bucketload of money selling PDP-11s. And when they stopped selling PDP-11s, the company essentially died! Could we find some citation somewhere that says the PDP-11 design was UN-sound? --Wtshymanski (talk) 15:11, 7 June 2011 (UTC)

In fairness, we should compare the PDP-11 to other contemporary designs of the time. The PDP-11 was based on a 16-bit word length and byte addressing, so it made logical and economic sense at that time to have a 16-bit address space. The extra 2 bits on the Unibus were viewed as enough "future-proofing", compared to other competing architectures. When DEC realized they needed still more address space, they added memory mapping hardware to extend it to 22 bits as an interim measure, and began working in earnest on the 32-bit VAX architecture. Gordon Bell and others commented extensively on the PDP-11 design tradeoffs in DEC's "Computer Engineering" book (Bell, Mudge, and Gray??? — I don't have my copy handy right now). The article needs more footnotes, and this book is a rich source, as well as the Cerruzzi book.

In the retrospective light of history, we should be careful not to harshly criticize an original design by rigorous modern standards from decades later. The mark of a "sound design" is its ability to be extended and adapted to future needs without requiring too much baroque and convoluted "kludging". For example, compare the "protected mode" and address extension implementations of the much-later IBM PC designs. The sheer amount of engineering time and end-user-visible kludging effort in extending the early PC designs stands in marked contrast to the relatively smooth transitions DEC offered its longtime customers, throughout the PDP-11 family, into the VAX family, and into the Alpha series.

The PDP-11 was announced as the "16-bit minicomputer architecture for the 70s", and the VAX was billed as the "32-bit superminicomputer architecture for the 80s" (DEC marketing brochures, again not at hand). DEC's 64-bit Alpha architecture was delayed by the departure of Gordon Bell (early 90s?) and managerial indecision, which put DEC off its pace, eventually dooming the company. Reify-tech (talk) 16:08, 7 June 2011 (UTC)

Obviously "bucketload" is not encyclopedic. Come on folks, there have been articles written on the PDP-11, so cite them. Gordon Bell's papers and books are a start. The policy clearly states any information not supported by a citation can be removed at any time. This whole section needs to be rewritten in encyclopedic language and be more precise. For example, by "design" do you mean architecture or implementation? Orthogonality of the instruction set as well as mass production are already discussed. And if you mean "commercially sucessful" then those words should be used, with citations to actual sales figures ro at least reliable published estimates. W Nowicki (talk) 16:19, 7 June 2011 (UTC)

We could always make a list of all the computer architectures introduced in 1970 that were still being sold 20 years later...shouldn't be that long...--Wtshymanski (talk) 16:28, 7 June 2011 (UTC)

This was a fight between hardware designers and programmers. The former thought it was just fine for the logical address space to be smaller than physical memory. The latter knew better. IBM was the one company at the time who got it and their 360 architecture is still around 45 years later. The 68000 and the '386 are also still with us, 31 and 26 years later. The 16-bit address space sank DEC, DG and every other computer company that built its architecture around it. Other than that it was a great success.--agr (talk) 21:39, 7 June 2011 (UTC)

PDP-11's weren't in the same niche. An apt comparison would be IBM 1130, which from your comments one might expect to see a large user community still around. TEDickey (talk) 22:53, 7 June 2011 (UTC)

We need to think in the context of 1970 minis. The 360 was a mainframe, rather than a mini - mainframes were expected to be costly while mini's sacrificed some capability to be more affordable. The 360 architecture survived for so long partly because its instruction format was relatively sparsely packed. IBM could add new instructions and new addressing modes to allow for higher memory requirements. But the 11 used very tightly packed instruction formats (probably to keep lower instruction decoder costs and memory access time), which allowed very little room for expansion. That may have doomed them in the long run but in 1970 the economics of building affordable machines would have dictated these sacrifices.

Memory getting cheaper is obvious to us with 20/20 hindsight but wasn't so obvious back then. Fully loaded systems (eg the 11/70) were generally run as multitasking systems. An 18 bit unibus address with only 16 bit addresses per application made sense for multitasking many small/medium size programs. Higher demands usually called for a machine in the next higher niche (eg one of the small mainframes).

But no matter what my ruminations are, if we want to say 'sound' or 'not sound' then we need some solid references.  Stepho  talk  05:15, 8 June 2011 (UTC)

I am thinking in the context of the 1970s. I spent the entire decade dealing with 64KB addressable machines and it was a pain. You'd develop whatever, customers liked it, they wanted more capabilities, happy to pay for them, then you'd hit memory limits, have to reconfigure into separate core loads, performance plummeted, everything got harder. Fixing a simple bug could involve a major rewrite if that coreload was out of memory. (I remember one case where we had already changed the manuals to say the bug was a feature when I figured out how to shoehorn in the fix.) The designers of the PDP-11 were aware memory was getting cheaper, hence the 18-bit initial physical limit. Your claim that "fully loaded systems (eg the 11/70) were generally run as multitasking systems" is not the way I remember things. DEC sold a lot of PDP-11 boxes for turnkey and embedded applications, such as CAD, typesetting, process control, communications switching, etc. Timesharing, though popular at universities, was not their biggest market by any means. I'm not saying the folks at DEC were idiots, just that they made a mistake limiting PDP-11 logical memory to 64KB. They had a great run with the PDP-11, but in the end I think that limit killed the company. I'm not sure I understand your IBM 1130 reference. It had a 15 bit address space with 16-bit words, so it had the same problems. In any case, IBM killed the follow on to the 1130 because it was too capable (according to a former boss who ran the project -- I believe it was code named Bimini.) Bottom line, though, I agree with you that we should not be rendering a sound or unsound judgement without a reliable, neutral source. --agr (talk) 23:38, 10 June 2011 (UTC)

Your experience is both greater and earlier than mine, so I will defer to you.  Stepho  talk  08:50, 11 June 2011 (UTC)

On the other hand, Arnold's experience is about on a par with mine. Reliable sources are what we're after, not reminiscences TEDickey (talk) 10:04, 11 June 2011 (UTC)

I think it's worth pointing out that history is complex, but I quit agree that article content should be based on reliable sources.--agr (talk) 23:51, 12 June 2011 (UTC)

Reorganization

This article should be reorganized to be inclusive of ALL PDP-11s, then separated by bus implementation, Unibus and Q-Bus implementation differences. As currently organized, it almost suggests the Q-Bus systems were not PDP-11s. In fact, the 11/83 & 11/84 used the identical CPU board and private memory interconnect.

Ggdr Gerry G 16:13, 16 July 2011 (UTC)

Not sure what your specific proposal is. It seems to be mentioning the Q-Bus systems already? In fact, there is a whole section on the LSI-11. My question is if "LSI-11" was an official product name, an internal project name, or the name of the chip etc. I would say it is a bit odd to have the lists of models in the middle of the article. Would this work better in, say, a table? or just a simpler list, and more prose to give a narrative version? I would be interested in the years each one was announced or delivered, for example, as well as how they technically related. And of course any sources you can dig up would be greatly appreciated, thanks. W Nowicki (talk) 18:58, 16 July 2011 (UTC)

Mention of PDP-11 simulator on "Super 8 (film)" viral marketing site

Ok, Spike-from-NH (and possibly others), I am in no way affiliated with that site. Why the hell would I care about the site? It's the fact that this was mentioned that is important. The fact that more people became aware of it. I don't know why you stubbornly keep on assuming that I have an ulterior motive for my addition. You can't just assume that people want to add things in because of "marketing" or "personal" agendas. All I want to do is put that people were able to know about this PDP-11 because of this usage of its interface or some other thing. In fact, that's how I came upon this article - because I read about it in the article on Wired, and went and searched it up, so I'm adding the fact that this was referenced as a sort of "back-reference" to the fact that this subject was mentioned, if you know what I mean. (This subject itself is so obscure and known to only a small number who have actually owned/operated one or are interested in it, so is there a problem with mentioning that people became aware of this computer because of a reference from something?) It's a big deal if this subject was referenced because so few people know about it. The content I added was supposed to document that fact that it was referenced, not for the links, which are only for verification and required citation. Maybe I might be weirdly and stubbornly clinging to the fact that this was referenced somewhere else in which more people found out about it, but still, a single sentence with a proper citation doesn't need to be removed. It's a freaking good-faith addition for goodness sakes! Why do you keep pushing it off and blocking? Comments and reasons appreciated, (and I did not understand a single bit of that last sentence you wrote in the edit overview summary, Spike. Please re-explain it in a clear manner.) - M0rphzone (talk) 21:48, 4 April 2012 (UTC)

I can say with confidence that no one using this article to study the PDP-11 cares that a viral video 20 years later used it as the theme of an advertisement, whereas the people producing the film and the ad campaign care greatly. The nature of this paragraph and its citation in this article is essentially trivia, which is discouraged (see Wikipedia:Handling trivia and Wikipedia:"In popular culture" content). I do not care who you are or aren't affiliated with. In your repeated attempts to plant this material into a Wikipedia article--and the above flame--you do seem to be using Wikipedia as a tool of a viral (def.: needing to attract eyes using any tactic) ad campaign. Spike-from-NH (talk) 23:47, 4 April 2012 (UTC)

Look here, the term "viral marketing" is a label that was used by the Wired article. Stop accusing me of having ulterior motives. I don't understand why you went for some personal attack by repeatedly saying I was attempting to market the site. Jeezus, all I was doing was using the same adjective! I don't care about marketing and I don't have a job yet or anything. Maybe I might be obsessing over a trivial thing, but still... I noticed the reference and the fact that this subject is relativity obscure. And seriously, why would I even care about any greedy monetary gain or any viral marketing. - M0rphzone (talk) 05:48, 5 April 2012 (UTC)

Hmm.... it seems that you possibly don't want certain info "tainting" the article or you want this article to have nothing to do with references from outside sources. Maybe that's why.... who knows. - M0rphzone (talk) 06:18, 5 April 2012 (UTC)

I'm willing to believe that M0rphzon is acting on good faith and is not related to the viral website. He has a point that the PDP-11 was mentioned on the website and that it introduces the PDP-11 to a new generation. However, WP:TRIVIA points out that unless that mention was important to the PDP-11 or public awareness of the PDP-11 or changed the world in some significant way then it should be discounted as useless trivia. Looking at the website, I see what appears to be a PDP-11 simulator booting. It shows boot messages containing 'RT11' in them and fragments of MAC-11 assembly code. But it also shows fragments of Unix C code. This leads me to suspect that it is only a simple text emulation controlled by a simple script, not a true binary emulator (although my last use of a PDP-11 was 1985 and my memory is a bit fuzzy). Also, is it important that it is specifically a PDP-11 or could it have equally well been an IBM 370, 8080 CP/M system or an Apple II? To me it looks like it could have been any computer from that era for the purposes of the movie and the viral ad. Lastly, has it really raised awareness of the PDP-11 among today's crowd? M0rphzon has obviously found his way here but my guess is that most people visiting that website didn't stay interested in the PDP-11 very long - if at all. The Super 8 (film) article has a fleeting mention of the PDP-11 and a link to here - that seems about the total amount of attention it really needs.  Stepho  talk  04:26, 5 April 2012 (UTC)

Thanks for attempting to verify and determine why it was referenced instead of stubbornly reverting. Maybe I shouldn't have been stubborn myself, or tried to have my way, but I thought this little bit could add to the article. I have to admit, it is a bit trivial, but I already took the effort to propose it and find the sources for it. And Spike's accusations didn't help change my thought; in fact, it just made me more stubborn and annoyed. - M0rphzone (talk) 06:02, 5 April 2012 (UTC)

One of my main reasons why I wanted to add this in was to reference the topic back to the reference(wikilink) from the Super 8 (film) article. - M0rphzone (talk) 06:21, 5 April 2012 (UTC)

Agree with Stepho. It doesn't matter whether you're affiliated with the site or not. For what relation the chatter that appears on "screen" at the Super-8 marketing site has to a real PDP-11 booting RT-11, there is nothing about either that compelled the use of these particular bits of old tech (had there been, you'd have more of an argument). The site could have equally well used the chatter from any similarly unfamiliar and cryptic OS.

Thus the note and the link do not provide information that adds to the reader's understanding of the PDP-11 or why it was notable. That is, in general, the standard of inclusion for material in WP articles. This fails to meet that standard. It's trivia, not encyclopedic, and WP leans strongly against "trivia" and "in popular culture" material (that's what the likes of Wired magazine are for).

The "back link" idea is not a compelling reason to ignore this policy. "Every outside site that links to a Wikipedia page should be linked back" is not a policy. Nor are internal Wikilinks encouraged to be symmetric. PDP-11 might be interesting to a small number of readers of Super 8 (film) but that does not necessarily mean the opposite is the case. People come here to learn about a computer. If they came here via internal or external articles about the film's marketing site, then they already know about that. Get it?

This may seem like an awful lot of argument time spent to keep this little item out of the article. But the reason WP:TRIVIA exists is that without it, trivia and "in popular culture" sections proliferate. Heck, they proliferate even with it. And WP is not written for seekers of trivia... not supposed to be, anyway. For the target audience of PDP-11 (people who want to learn about the computer and why it was notable) this information and the reference link would be a waste of their time.

All of the above would go double--heck, squared, at least--if we were talking about a simple external link (see WP:ELNO).

Sorry about the time spent to find a source, but that won't carry any arguments either. Jeh (talk) 17:23, 5 April 2012 (UTC)

Meh, I already knew it was trivial. Thanks for providing a thorough explanation for opposing it. That's what I want to see/know. The only reason I even started edit-warring was because of Spike's inadequate reasons/explanations and "resentful/hostile" attitude. He continued to insist that I was attempting to game the system or use Wikipedia as a tool. I would've liked an apology, but forget it. - M0rphzone (talk) 22:29, 5 April 2012 (UTC)

How fast was it?

20 Mhz, 16 Mhz, 12 Mhz, 10 Mhz? Ebaychatter0 (talk) 14:00, 19 November 2012 (UTC)

Still looking for a nice compact table - but cycle times I've seen in ads mention 500 ns down to 300 ns - 2 Megahertz up to 3 1/3 MHZ. I think the LSI models ran faster but still not in the double-digits range. Still looking for a better source than "Computerworld" ads. --Wtshymanski (talk) 17:49, 19 November 2012 (UTC)

But the LSI models were microprogrammed. They might have "run faster" but the time to execute an instruction did not improve on the discrete-logic models. The Western Digital chipset was the most compact implementation of a PDP-11 to date, but not the snappiest. Can't help with specifics, but it would be a good addition to the article, for completeness as well as historical perspective. Spike-from-NH (talk) 19:52, 19 November 2012 (UTC)

I have a PDP-11/70 Processor Handbook from 1975 that has an Appendix C on instruction timing. It's complicated. The timing had up to three components, Execute/Fetch time and the time required for the source and destination. The last two components depended greatly on which addressing mode was used. One example given was an ADD A,B with addressing mode 6 (indexed). In that case, source and destination times were 0.6 microseconds each, plus an Execution/Fetch time of 1.35 microseconds for a total instruction of 2.55 microseconds. And that assumed all cache hits. Each cache miss added 1.02 microseconds. Floating point was even more complex, since there was some overlap, but in general it was significantly slower. Any thoughts as to what to include in the article? I can supply more data, if needed.--agr (talk) 01:52, 20 November 2012 (UTC)

Wow--and in my experience, the 11/70 was the prevailing big-daddy multi-user machine until the VAX came along. The timing algorithms will be different for different models; for a good sample, the article might include three or four standard instructions of your choosing, with timings for the original model (11/20), the minimalist 11/05, the LSI-11, and the 11/70 or perhaps the fastest PDP-11 that DEC made. Spike-from-NH (talk) 02:24, 20 November 2012 (UTC)

A short table showing three representative early, middle and late models, with one or two different instructions, with all the special cases (cache miss, address modes) would be illuminating and would help explain to the reader just how complicated the idea of instruction timing really is. The type of person interested in megahertz drag racing will be a little disappointed that she's not getting a simple number, but a simple number is wrong anyway. A more thoughtful reader might even wonder why modern machines with thousands of times faster processors and larger memories seem not to be doing things thousands of times faster, on the whole. But that's off topic for this article. --Wtshymanski (talk) 15:04, 20 November 2012 (UTC)

Agreed that some instructions take longer than others. But if you take a 6502 speced at 1Mhz and a PIC controller spec-ed at 20Mhz, you can at least conclude that the present day PIC is 20 times faster than the vintage 6502 *at least on register-to-register move* since both can do register to register move in 1 clock cycle. Ebaychatter0 (talk) 18:50, 20 November 2012 (UTC)