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The '''PDP-11''' is a series of [[minicomputer]]s introduced in 1969 [1] by the [[Digital Equipment Corporation]] (DEC), in production by them from 1970-1990. Their life-time spanned a period of momentous changes in the computer world: when they were first introduced [[integrated circuit]]s had just been introduced (small ones, containing only a few simple [[gate]]s); and for a little less than half their life, [[core memory]] was still the standard [[main memory]] technology. By the end, the now-ubiquitous [[microprocessor]]s and [[dynamic RAM]] had completely taken over.

[[Image:KA11FrontPanel.jpg|right|thumb|300px|[[Front panel]] of the [[KA11 CPU|KA11]], the first PDP-11 model]]

It was the machine which made [[UNIX]], which now seems to have taken over the world (in the form of [[Linux]]) widely known and popular.

The machine [[word]] size was 16 bits, and it was a [[general register]] [[architecture]]. Although it was not the first to feature the latter, its wide distribution (in 1980, it was the world's best-selling computer) and its novel addressing modes (below) have helped influence almost all later machines to follow that path.

(For more information about the architecture, including its innovative and much-copied [[stack]]-oriented [[PDP-11 architecture#Addressing modes|addressing modes]], see [[PDP-11 architecture|here]].)

PDP-11's came in two groups: those which used the [[UNIBUS]] for a bus, and the later ones which used the [[QBUS]]. Eventually DEC stopped producing [[UNIBUS]] PDP-11's (the last were the [[PDP-11/44]] and [[PDP-11/24]]); later 'UNIBUS' machines (the [[PDP-11/84]] and [[PDP-11/94]]) actually contained QBUS processors with a QBUS<->UNIBUS adapter board.

Towards the end of its life, there were several microprocessor implementations of the PDP-11, as [[integrated circuit|chips]]. After DEC discontinued production of PDP-11's, the line was sold to [[Mentec]], who produced a few newer models.

== PDP-11 Models and notes ==

{| class="wikitable"
! Model !! Introduced !! Bus Type !! Addressing !! Split I & D !! Notes !! Speed (VUPS)
|-
| [[PDP-11/20|11/20]] || 1969[1] ||[[UNIBUS]] || 16-bit || no || ||
|-
| [[PDP-11/05|11/05]] || 1972 || UNIBUS || 16-bit || no || OEM model ||
|-
| [[PDP-11/10|11/10]][*] || 1972 || UNIBUS || 16-bit || no || ||
|-
| [[PDP-11/15|11/15]] || 1972 || UNIBUS || 16-bit || no || OEM model ||
|-
| [[PDP-11/35|11/35]] || 1973 || UNIBUS || 18-bit || no || OEM model ||
|-
| [[PDP-11/40|11/40]] || 1973 || UNIBUS || 18-bit || no || ||
|-
| [[PDP-11/45|11/45]] || 1973 || UNIBUS || 18-bit || yes || core memory ||
|-
| [[PDP-11/50|11/50]] || 1975 || UNIBUS || 18-bit || yes || [[Metal Oxide Semiconductor|MOS]] memory ||
|-
| [[PDP-11/55|11/55]] || 1976 || UNIBUS || 18-bit || yes || fast bipolar memory ||
|-
| [[PDP-11/70|11/70]] || 1975 || UNIBUS || 22-bit || yes || || 0.6
|-
| [[PDP-11/03|11/03]] || 1975 || [[QBUS]] || 16-bit || no || first QBUS model || 0.05
|-
| [[PDP-11/04|11/04]] || 1976 || UNIBUS || 16-bit || no || || 0.11
|-
| [[PDP-11/34|11/34]] || 1976 || UNIBUS || 18-bit || no || || 0.21
|-
| [[PDP-11/60|11/60]] || 1977 || UNIBUS || 18-bit || no || writable control store || 
|-
| [[PDP-11/23|11/23]] || 1979 || QBUS || 18-bit ''or'' 22-bit || no || first [[F-11]] || 0.12
|-
| [[PDP-11/24|11/24]] || 1979 || UNIBUS || 22-bit || no || only UNIBUS model to use F-11 chip || 0.18
|-
| [[PDP-11/44|11/44]] || 1979 || UNIBUS || 22-bit || yes || last non-LSI PDP-11 || 0.42
|-
|[[PDP-11/23-PLUS|11/23+]] || 1981 Nov || QBUS || 22-bit || no || || 0.18
|-
| [[PDP-11/73|11/73]] || 1983 || QBUS || 22-bit || yes || first [[J-11]] machine, 15MHz, integrated [[FPU]], also first [[PMI]] PDP-11 || 0.45
|-
| [[PDP-11/53|11/53]] || 1984 || QBUS || 22-bit || yes || S-box or standard QBUS, integrated FPU, 768KiW memory || 0.29
|-
| [[PDP-11/83|11/83]] || 1988 || QBUS || 22-bit || yes || J-11 at 18MHz, integrated FPU || 0.72
|-
| [[PDP-11/84|11/84]] || 1988 || UNIBUS || 22-bit || yes || J-11 at 18MHz, integrated FPU || 0.72
|-
| [[PDP-11/93|11/93]] || 1990 || QBUS || 22-bit || yes || J-11 at 18MHz, integrated FPU, 2MiW onboard memory || 1.0
|-
| [[PDP-11/94|11/94]] || 1990 || UNIBUS || 22-bit || yes || J-11 at 18MHz, integrated FPU, 2MiW onboard memory || 1.0
|}

''<span style="font-size:70%">[*]The name PDP-11/10 was recycled by DEC from an earlier [[KA11 CPU]]-based 11/10 from 1969, or at least it existed in advertisements[1]</span>''

==Operating Systems==

There were a number of well-known [[operating system]]s for the PDP-11. Many were produced by [[DEC]] themselves, but several were produced by third-parties. Often DEC would purchase or re-brand such an OS and re-sell it as their own product; for example, UNIX sold as [[Ultrix]] by DEC.

UNIX was not originally a PDP-11 system (it was born on the [[PDP-7]]), but it moved to the PDP-11 shortly after it was first created, and spread widely there (since PDP-11's were common machines, due to their relatively low cost and good engineering), with the real explosion of use starting with [[UNIX Sixth Edition]].

===UNIX===

* [[UNIX First Edition]]
* [[UNIX Second Edition]]
* [[UNIX Third Edition]]
* [[UNIX Fourth Edition]]
* [[UNIX Fifth Edition]]
* [[UNIX Sixth Edition]]
* [[Unix Seventh Edition]]

These are the original Bell Laboratories releases of Unix; the first 4 were only internal to Bell, the Fifth saw limited distribution outside it, and the Sixth took over the world.

* [[LSX]]
* [[MINI-UNIX]]

For PDP-11's without [[memory management]].

* [[System III]]

This was the first shipping Unix distro by AT&T. It only supported the PDP-11 and [[VAX]] computers.

* [[2.9 BSD]]

This version was a port of the [[4.3 BSD]] feature set to the PDP-11.  Although considered an impossible goal by many, it accomplished this by using [[overlay]]s for portions of the [[kernel]], and to allow for user programs larger than 64KB.

* [[2.10 BSD]]
* [[2.11 BSD]]

This last version is still supported, and if one really felt the need to load a Unix for use on a PDP-11 this would be the best fit. It has support for [[TCP/IP]], large memory space and is the best UNIX experience one can get going to get on a 16-bit mini.

===DEC OS's===

* [[DOS-11]]
* [[RSX-11]]
* [[RSTS/E]] - a descendant of [[RSTS-11]]
* [[RT-11]]
* [[IAS]]

Technically also an OS is [[XXDP diagnostic package|XXDP]], which is an 'overseer' for running the PDP-11 [[diagnostic]]s produced/provided by DEC.

===Real-time OS's===

PDP-11's were very popular in [[real-time]] and [[data network]]ing uses; a number of OS's were developed for such environments:

* [[ANTS terminal system|ANTS]]
* [[ELF operating system|ELF]]
* [[MOS operating system|MOS]] - an ELF descendant
* [[MERT operating system|MERT]] - another Bell system
* [[MINITS]] - network appliance framework

===Miscellaneous===

* [[SITS]] - "Small [[Incompatible Timesharing System|ITS]]" for running Logo
* [[Camexec]] - hosted the Camex typesetting system
* Trantor - written for the MIT Applied Mathematics Department

==Simulators==

There a number of good [[simulator]]s for the PDP-11:

* [[SIMH]]
* [[Ersatz-11]]

The latter is less well known than the ubiquitous SIMH, but is very fast; simulated systems running on Ersatz-11 are usually faster than real PDP-11's.

==New Emulator Hardware==

* [[UniBone/QBone]]

==See also==

* [[PDP-11 architecture]]
* [[PDP-11 Memory Management]]
* [[UNIBUS memories]]
* [[QBUS memories]]
* [[UNIBUS boot ROMs]]
* [[QBUS boot ROMs]]
* [[H95xx-H96xx Series of DEC Cabinets and Accessories]]
* [[List of VAX models with PDP-11 compatibility mode]]
* [[PDP11GUI]]

==External links==

* [http://www.bitsavers.org/pdf/dec/pdp11/ PDP11] - Documentation at [[Bitsavers]]
** [http://www.bitsavers.org/pdf/dec/pdp11/memos/ memos] - Interesting internal DEC memos about the PDP-11
*** [http://www.bitsavers.org/pdf/dec/pdp11/memos/690111_How_Good_Is_The_PDP-11.pdf How Good is the PDP-11?] - interesting early comparison with competitors
* [https://gordonbell.azurewebsites.net/Digital/PDP%2011%20Handbook%201969.pdf PDP-11 Handbook (1969)]
* [http://s3data.computerhistory.org/brochures/dec.pdp-11.1977.102646131.pdf PDP-11 Variations on a Theme] - marketing brochure from DEC
* [https://gordonbell.azurewebsites.net/CGB%20Files/New%20Architecture%20PDP11%20SJCC%201970%20c.pdf A new architecture for mini-computers - The DEC PDP-11] - the [[AFIPS]] paper which introduced the PDP-11
* [http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/PDP-11_Models.html PDP-11 Recognition] - Illustrated guide to identifying PDP-11 models
* [https://hampage.hu/pdp-11/ PDP-11]
** [https://hampage.hu/pdp-11/main.html The Pre-Life of a Legend is another Legend]
** [http://hampage.hu/pdp-11/birth.html How the PDP-11 Was Born (according to Larry McGowan)]
* [https://pdp-11.org/ PDP-11 history and links to materials]
* [https://www.pdp-11.nl/ Henk's DIGITAL computer room] - an amazing collection of PDP-11's
* [https://arstechnica.com/gadgets/2022/03/a-brief-tour-of-the-pdp-11-the-most-influential-minicomputer-of-all-time/ A brief tour of the PDP-11, the most influential minicomputer of all time] - has some minor errors, but generally good
* [https://gordonbell.azurewebsites.net/Digital/PDP11_Arch_Enhance_Strategy_75.pdf Proposal for PDP-11 I/O Architecture]
* [http://gordonbell.azurewebsites.net/cgb%20files/what%20have%20we%20learned%20from%20the%20pdp-11%201977%20c.pdf What Have we Learned From the PDP-11?] - a retrospective on a group of papers by Gordon Bell
* [https://gordonbell.azurewebsites.net/Digital/Bell_Strecker_What_we%20_learned_fm_PDP-11c%207511.pdf Computer Structures: What Have we Learned From the PDP-11?]

==References==

* [http://vintagecomputer.net/digital/PDP11-20/PDP11_Price-List_19691215.pdf PDP-11/20 Price List]

{{PDP-11}}

[[Category: PDP-11s]]
[[Category: DEC Architectures]]
[[Category: 16-bit Computers‎]]