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This article is about the PDP-11 series of minicomputers. PDP-11_sentence_0

For the PDP-11 processor architecture, see PDP-11 architecture. PDP-11_sentence_1


DeveloperPDP-11_header_cell_0_0_0 Digital Equipment CorporationPDP-11_cell_0_0_1
Product familyPDP-11_header_cell_0_1_0 Programmed Data ProcessorPDP-11_cell_0_1_1
TypePDP-11_header_cell_0_2_0 MinicomputerPDP-11_cell_0_2_1
Release datePDP-11_header_cell_0_3_0 1970; 50 years ago (1970)PDP-11_cell_0_3_1
Units soldPDP-11_header_cell_0_4_0 around 600,000PDP-11_cell_0_4_1
Operating systemPDP-11_header_cell_0_5_0 BATCH-11/DOS-11, DSM-11, IAS, P/OS, RSTS/E, RSX-11, RT-11, Ultrix-11PDP-11_cell_0_5_1
PlatformPDP-11_header_cell_0_6_0 DEC 16-bitPDP-11_cell_0_6_1
SuccessorPDP-11_header_cell_0_7_0 VAX-11PDP-11_cell_0_7_1

The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a set of products in the Programmed Data Processor (PDP) series. PDP-11_sentence_2

In total, around 600,000 PDP-11s of all models were sold, making it one of DEC's most successful product lines. PDP-11_sentence_3

The PDP-11 is considered by some experts to be the most popular minicomputer. PDP-11_sentence_4

The PDP-11 included a number of innovative features in its instruction set and additional general-purpose registers that made it much easier to program than earlier models in the PDP series. PDP-11_sentence_5

Additionally, the innovative Unibus system allowed external devices to be easily interfaced to the system using direct memory access, opening the system to a wide variety of peripherals. PDP-11_sentence_6

The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years. PDP-11_sentence_7

The ease of programming of the PDP-11 made it very popular for general-purpose computing uses as well. PDP-11_sentence_8

The design of the PDP-11 inspired the design of late-1970s microprocessors including the Intel x86 and the Motorola 68000. PDP-11_sentence_9

The design features of PDP-11 operating systems, and other operating systems from Digital Equipment, influenced the design of operating systems such as CP/M and hence also MS-DOS. PDP-11_sentence_10

The first officially named version of Unix ran on the PDP-11/20 in 1970. PDP-11_sentence_11

It is commonly stated that the C programming language took advantage of several low-level PDP-11–dependent programming features, albeit not originally by design. PDP-11_sentence_12

An effort to expand the PDP-11 from 16 to 32-bit addressing led to the VAX-11 design, which took part of its name from the PDP-11. PDP-11_sentence_13

History PDP-11_section_0

Previous machines PDP-11_section_1

In 1963, DEC introduced what is considered to be the first commercial minicomputer in the form of the PDP-5. PDP-11_sentence_14

This was a 12-bit design adapted from the 1962 LINC machine that was intended to be used in a lab setting. PDP-11_sentence_15

DEC slightly simplified the LINC system and instruction set, aiming the PDP-5 at smaller settings that did not need the power of their larger 18-bit PDP-4. PDP-11_sentence_16

The PDP-5 was a success, ultimately selling about 50,000 examples. PDP-11_sentence_17

During this period, the computer market was moving from computer word lengths based on units of 6 bits to units of 8 bits, following the introduction of the 7-bit ASCII standard. PDP-11_sentence_18

In 1967–1968, DEC engineers designed a 16-bit machine, the PDP-X, but management ultimately canceled the project as it did not appear to offer a significant advantage over their existing 12- and 18-bit platforms. PDP-11_sentence_19

Several of the engineers from the PDP-X left DEC and formed Data General. PDP-11_sentence_20

The next year they introduced the 16-bit Data General Nova. PDP-11_sentence_21

The Nova was a major success, selling tens of thousands of units and launching what would become one of DEC's major competitors through the 1970s and 1980s. PDP-11_sentence_22

Release PDP-11_section_2

A subsequent effort, code-named "Desk Calculator", looked at a variety of options before choosing what became the 16-bit PDP-11; The PDP-11 family was announced in January 1970 and shipments began early that year. PDP-11_sentence_23

DEC sold over 170,000 PDP-11s in the 1970s. PDP-11_sentence_24

Initially manufactured of small-scale transistor–transistor logic, a single-board large scale integration version of the processor was developed in 1975. PDP-11_sentence_25

A two-or-three-chip processor, the J-11 was developed in 1979. PDP-11_sentence_26

The last models of the PDP-11 line were the PDP-11/94 and PDP-11/93 introduced in 1990. PDP-11_sentence_27

Innovative features PDP-11_section_3

Instruction set orthogonality PDP-11_section_4

See also: PDP-11 architecture PDP-11_sentence_28

The PDP-11 processor architecture has a mostly orthogonal instruction set. PDP-11_sentence_29

For example, instead of instructions such as load and store, the PDP-11 has a move instruction for which either operand (source and destination) can be memory or register. PDP-11_sentence_30

There are no specific input or output instructions; the PDP-11 uses memory-mapped I/O and so the same move instruction is used; orthogonality even enables moving data directly from an input device to an output device. PDP-11_sentence_31

More complex instructions such as add likewise can have memory, register, input, or output as source or destination. PDP-11_sentence_32

Most operands can apply any of eight addressing modes to eight registers. PDP-11_sentence_33

The addressing modes provide register, immediate, absolute, relative, deferred (indirect), and indexed addressing, and can specify autoincrementation and autodecrementation of a register by one (byte instructions) or two (word instructions). PDP-11_sentence_34

Use of relative addressing lets a machine-language program be position-independent. PDP-11_sentence_35

No dedicated I/O instructions PDP-11_section_5

Early models of the PDP-11 had no dedicated bus for input/output, but only a system bus called the Unibus, as input and output devices were mapped to memory addresses. PDP-11_sentence_36

An input/output device determined the memory addresses to which it would respond, and specified its own interrupt vector and interrupt priority. PDP-11_sentence_37

This flexible framework provided by the processor architecture made it unusually easy to invent new bus devices, including devices to control hardware that had not been contemplated when the processor was originally designed. PDP-11_sentence_38

DEC openly published the basic Unibus specifications, even offering prototyping bus interface circuit boards, and encouraging customers to develop their own Unibus-compatible hardware. PDP-11_sentence_39

The Unibus made the PDP-11 suitable for custom peripherals. PDP-11_sentence_40

One of the predecessors of Alcatel-Lucent, the Bell Telephone Manufacturing Company, developed the BTMC DPS-1500 packet-switching (X.25) network and used PDP-11s in the regional and national network management system, with the Unibus directly connected to the DPS-1500 hardware. PDP-11_sentence_41

Higher-performance members of the PDP-11 family, starting with the PDP-11/45 Unibus and 11/83 Q-bus systems, departed from the single-bus approach. PDP-11_sentence_42

Instead, memory was interfaced by dedicated circuitry and space in the CPU cabinet, while the Unibus continued to be used for I/O only. PDP-11_sentence_43

In the PDP-11/70, this was taken a step further, with the addition of a dedicated interface between disks and tapes and memory, via the Massbus. PDP-11_sentence_44

Although input/output devices continued to be mapped into memory addresses, some additional programming was necessary to set up the added bus interfaces. PDP-11_sentence_45

Interrupts PDP-11_section_6

The PDP-11 supports hardware interrupts at four priority levels. PDP-11_sentence_46

Interrupts are serviced by software service routines, which could specify whether they themselves could be interrupted (achieving interrupt nesting). PDP-11_sentence_47

The event that causes the interrupt is indicated by the device itself, as it informs the processor of the address of its own interrupt vector. PDP-11_sentence_48

Interrupt vectors are blocks of two 16-bit words in low kernel address space (which normally corresponded to low physical memory) between 0 and 776. PDP-11_sentence_49

The first word of the interrupt vector contains the address of the interrupt service routine and the second word the value to be loaded into the PSW (priority level) on entry to the service routine. PDP-11_sentence_50

The article on PDP-11 architecture provides more details on interrupts. PDP-11_sentence_51

Designed for mass production PDP-11_section_7

The PDP-11 was designed for ease of manufacture by semiskilled labor. PDP-11_sentence_52

The dimensions of its pieces were relatively non-critical. PDP-11_sentence_53

It used a wire-wrapped backplane. PDP-11_sentence_54

LSI-11 PDP-11_section_8

The LSI-11 (PDP-11/03), introduced in February 1975 is the first PDP-11 model produced using large-scale integration; the entire CPU is contained on four LSI chips made by Western Digital (the MCP-1600 chip set; a fifth chip can be added to extend the instruction set, as pictured on the right). PDP-11_sentence_55

It uses a bus which is a close variant of the Unibus called the LSI Bus or Q-Bus; it differs from the Unibus primarily in that addresses and data are multiplexed onto a shared set of wires rather than having separate sets of wires. PDP-11_sentence_56

It also differs slightly in how it addresses I/O devices and it eventually allowed a 22-bit physical address (whereas the Unibus only allows an 18-bit physical address) and block-mode operations for significantly improved bandwidth (which the Unibus does not support). PDP-11_sentence_57

The CPU microcode includes a debugger: firmware with a direct serial interface (RS-232 or current loop) to a terminal. PDP-11_sentence_58

This lets the operator do debugging by typing commands and reading octal numbers, rather than operating switches and reading lights, the typical debugging method at the time. PDP-11_sentence_59

The operator can thus examine and modify the computer's registers, memory, and input/output devices, diagnosing and perhaps correcting failures in software and peripherals (unless a failure disables the microcode itself). PDP-11_sentence_60

The operator can also specify which disk to boot from. PDP-11_sentence_61

Both innovations increased the reliability and decreased the cost of the LSI-11. PDP-11_sentence_62

Later Q-Bus based systems such as the LSI-11/23, /73, and /83 are based upon chip sets designed in house by Digital Equipment Corporation. PDP-11_sentence_63

Later PDP-11 Unibus systems were designed to use similar Q-Bus processor cards, using a Unibus adapter to support existing Unibus peripherals, sometimes with a special memory bus for improved speed. PDP-11_sentence_64

There were other significant innovations in the Q-Bus lineup. PDP-11_sentence_65

For example, a system variant of the PDP-11/03 introduced full system power-on self-test (POST). PDP-11_sentence_66

Decline PDP-11_section_9

The basic design of the PDP-11 was flexible, and was continually updated to use newer technologies. PDP-11_sentence_67

However, the limited throughput of the Unibus and Q-bus started to become a system-performance , and the 16-bit logical address limitation hampered the development of larger software applications. PDP-11_sentence_68

The article on PDP-11 architecture describes the hardware and software techniques used to work around address-space limitations. PDP-11_sentence_69

DEC's 32-bit successor to the PDP-11, the VAX (for "Virtual Address eXtension") overcame the 16-bit limitation, but was initially a superminicomputer aimed at the high-end time-sharing market. PDP-11_sentence_70

The early VAX CPUs provided a PDP-11 compatibility mode under which much existing software could be immediately used, in parallel with newer 32-bit software, but this capability was dropped with the first MicroVAX. PDP-11_sentence_71

For a decade, the PDP-11 was the smallest system that could run Unix, but in the 1980s, the IBM PC and its clones largely took over the small computer market; BYTE in 1984 reported that the PC's Intel 8088 microprocessor outperformed the PDP-11/23 when running Unix. PDP-11_sentence_72

Newer microprocessors such as the Motorola 68000 (1979) and Intel 80386 (1985) also included 32-bit logical addressing. PDP-11_sentence_73

The 68000 in particular facilitated the emergence of a market of increasingly powerful scientific and technical workstations that would often run Unix variants. PDP-11_sentence_74

These included the HP 9000 series 200 (starting with the HP 9826A in 1981) and 300/400, with the HP-UX system being ported to the 68000 in 1984; Sun Microsystems workstations running SunOS, starting with the Sun-1 in 1982; Apollo Domain workstations starting with the DN100 in 1981 running Domain/OS, which was proprietary but offered a degree of Unix compatibility; and the Silicon Graphics IRIS range, which developed into Unix-based workstations by 1985 (IRIS 2000). PDP-11_sentence_75

Personal computers based on the 68000 like the Apple Lisa and Macintosh or the Commodore Amiga arguably constituted less of a threat to DEC's business, although technically these systems could also run Unix derivatives. PDP-11_sentence_76

In the early years, in particular, Microsoft's Xenix was ported to systems like the TRS-80 Model 16 (with up to 1 MB of memory) in 1983, and to the Apple Lisa, with up to 2 MB of installed RAM, in 1984. PDP-11_sentence_77

The mass-production of those chips eliminated any cost advantage for the 16-bit PDP-11. PDP-11_sentence_78

A line of personal computers based on the PDP-11, the DEC Professional series, failed commercially, along with other non-PDP-11 PC offerings from DEC. PDP-11_sentence_79

In 1994 DEC sold the PDP-11 system-software rights to Mentec Inc., an Irish producer of LSI-11 based boards for Q-Bus and ISA architecture personal computers, and in 1997 discontinued PDP-11 production. PDP-11_sentence_80

For several years, Mentec produced new PDP-11 processors. PDP-11_sentence_81

Other companies found a niche market for replacements for legacy PDP-11 processors, disk subsystems, etc. PDP-11_sentence_82

By the late 1990s, not only DEC but most of the New England computer industry which had been built around minicomputers similar to the PDP-11 collapsed in the face of microcomputer-based workstations and servers. PDP-11_sentence_83

Models PDP-11_section_10

The PDP-11 processors tend to fall into several natural groups depending on the original design upon which they are based and which I/O bus they use. PDP-11_sentence_84

Within each group, most models were offered in two versions, one intended for OEMs and one intended for end-users. PDP-11_sentence_85

Although all models share the same instruction set, later models added new instructions and interpreted certain instructions slightly differently. PDP-11_sentence_86

As the architecture evolved, there were also variations in handling of some processor status and control registers. PDP-11_sentence_87

Unibus models PDP-11_section_11

The following models use the Unibus as their principal bus: PDP-11_sentence_88


  • PDP-11/20 and PDP-11/15 — 1970. The 11/20 sold for $11,800. The original, non-microprogrammed processor; designed by Jim O'Loughlin. Floating point is supported by peripheral options using various data formats. The 11/20 lacks any kind of memory protection hardware unless retrofitted with a KS-11 memory mapping add-on. There was also a very stripped-down 11/20 at first called the 11/10, but this number was later re-used for a different model (see below).PDP-11_item_0_0
  • PDP-11/45 (1972), PDP-11/50 (1975), and PDP-11/55 (1976) – A much faster microprogrammed processor that can use up to 256 kB of semiconductor memory instead of or in addition to core memory; support memory mapping and protection. First model to support an optional FP11 floating-point coprocessor, which established the format used in later models.PDP-11_item_0_1
  • PDP-11/35 and PDP-11/40 – 1973. Microprogrammed successors to the PDP-11/20; the design team was led by Jim O'Loughlin.PDP-11_item_0_2
  • PDP-11/05 and PDP-11/10 – 1972. A cost-reduced successor to the PDP-11/20.PDP-11_item_0_3
  • PDP-11/70 – 1975. The 11/45 architecture expanded to allow 4 MB of physical memory segregated onto a private memory bus, 2 kB of cache memory, and much faster I/O devices connected via the Massbus.PDP-11_item_0_4
  • PDP-11/34 (1976) and PDP-11/04 (1975) – Cost-reduced follow-on products to the 11/35 and 11/05; the PDP-11/34 concept was created by Bob Armstrong. The 11/34 supports up to 256 kB of Unibus memory. The PDP-11/34a (1978) supports a fast floating-point option, and the 11/34c (same year) supported a cache memory option.PDP-11_item_0_5
  • PDP-11/60 – 1977. A PDP-11 with user-writable microcontrol store; this was designed by another team led by Jim O'Loughlin.PDP-11_item_0_6
  • PDP-11/44 – 1979. A replacement for the 11/45 and 11/70, introduced in 1980, that supports optional (though apparently always included) cache memory, FP-11 floating-point processor (one circuit board, using sixteen AMD Am2901 bit slice processors), and commercial instruction set (CIS, two boards). It includes a sophisticated serial console interface and support for 4 MB of physical memory. The design team was managed by John Sofio. This was the last PDP-11 processor to be constructed using discrete logic gates; later models were all microprocessor-based. It was also the last PDP-11 architecture created by Digital Equipment Corporation, later models were VLSI chip realizations of the existing system architectures.PDP-11_item_0_7
  • PDP-11/24 – 1979. First VLSI PDP-11 for Unibus, using the "Fonz-11" (F11) chip set with a Unibus adapter.PDP-11_item_0_8
  • PDP-11/84 – 1985-1986. Using the VLSI "Jaws-11" (J11) chip set with a Unibus adapter.PDP-11_item_0_9
  • PDP-11/94 – 1990. J11-based, faster than 11/84.PDP-11_item_0_10

Q-bus models PDP-11_section_12

The following models use the Q-Bus as their principal bus: PDP-11_sentence_89


  • PDP-11/03 (also known as the LSI-11/03) – The first PDP-11 implemented with large-scale integration ICs, this system uses a four-package MCP-1600 chipset from Western Digital and supports 60 kB of memory.PDP-11_item_1_11
  • PDP-11/23 – Second generation of LSI (F-11). Early units supported only 248 kB of memory.PDP-11_item_1_12
  • PDP-11/23+/MicroPDP-11/23 – Improved 11/23 with more functions on the (larger) processor card. By mid-1982, the 11/23+ supported 4mb of memory.PDP-11_item_1_13
  • MicroPDP-11/73 – The third generation LSI-11, this system uses the faster "Jaws-11" (J-11) chip set and supports up to 4 MB of memory.PDP-11_item_1_14
  • MicroPDP-11/53 – Slower 11/73 with on-board memory.PDP-11_item_1_15
  • MicroPDP-11/83 – Faster 11/73 with PMI (private memory interconnect).PDP-11_item_1_16
  • MicroPDP-11/93 – Faster 11/83; final DEC Q-Bus PDP-11 model.PDP-11_item_1_17
  • KXJ11 – QBUS card (M7616) with PDP-11 based peripheral processor and DMA controller. Based on a J11 CPU equipped with 512 kB of RAM, 64 kB of ROM, and parallel and serial interfaces.PDP-11_item_1_18
  • Mentec M100 – Mentec redesign of the 11/93, with J-11 chipset at 19.66 MHz, four on-board serial ports, 1-4 MB of on-board memory, and optional FPU.PDP-11_item_1_19
  • Mentec M11 – Processor upgrade board; microcode implementation of PDP-11 instruction set by Mentec, using the TI 8832 ALU and TI 8818 microsequencer from Texas Instruments.PDP-11_item_1_20
  • Mentec M1 – Processor upgrade board; microcode implementation of PDP-11 instruction set by Mentec, using Atmel 0.35 μm ASIC.PDP-11_item_1_21
  • Quickware QED-993 – High performance PDP-11/93 processor upgrade board.PDP-11_item_1_22
  • DECserver 500 and 550 LAT terminal servers DSRVS-BA using the KDJ11-SB chipsetPDP-11_item_1_23

Models without standard bus PDP-11_section_13


  • PDT-11/110PDP-11_item_2_24
  • PDT-11/130PDP-11_item_2_25
  • PDT-11/150PDP-11_item_2_26

The PDT series were desktop systems marketed as "smart terminals". PDP-11_sentence_90

The /110 and /130 were housed in a VT100 terminal enclosure. PDP-11_sentence_91

The /150 was housed in a table-top unit which included two 8-inch floppy drives, three asynchronous serial ports, one printer port, one modem port and one synchronous serial port and required an external terminal. PDP-11_sentence_92

All three employed the same chipset as used on the LSI-11/03 and LSI-11/2 in four "microm"s. There is an option which combines two of the microms into one dual carrier, freeing one socket for an EIS/FIS chip. PDP-11_sentence_93

The /150 in combination with a VT105 terminal was also sold as MiniMINC, a budget version of the MINC-11. PDP-11_sentence_94


  • PRO-325PDP-11_item_3_27
  • PRO-350PDP-11_item_3_28
  • PRO-380PDP-11_item_3_29

The DEC Professional series are desktop PCs intended to compete with IBM's earlier 8088 and 80286 based personal computers. PDP-11_sentence_95

The models are equipped with 5¼ inch floppy disk drives and hard disks, except the 325 which has no hard disk. PDP-11_sentence_96

The original operating system was P/OS, which was essentially RSX-11M+ with a menu system on top. PDP-11_sentence_97

As the design was intended to avoid software exchange with existing PDP-11 models, their ill fate in the market was no surprise for anyone except DEC. PDP-11_sentence_98

The RT-11 operating system was eventually ported to the PRO series. PDP-11_sentence_99

A port of RSTS/E to the PRO series was also done internal to DEC, but it was not released. PDP-11_sentence_100

The PRO-325 and -350 units are based on the DCF-11 ("Fonz") chipset, the same as found in the 11/23, 11/23+ and 11/24. PDP-11_sentence_101

The PRO-380 is based on the DCJ-11 ("Jaws") chipset, the same as found in the 11/53,73,83 and others, though running only at 10 MHz because of limitations in the support chipset. PDP-11_sentence_102

Models that were planned but never introduced PDP-11_section_14


  • PDP-11/27 – A Jaws-11 implementation that would have used the VAXBI Bus as its principal I/O bus.PDP-11_item_4_30
  • PDP-11/68 – A follow-on to the PDP-11/60 that would have supported 4 MB of physical memory.PDP-11_item_4_31
  • PDP-11/74 – A PDP-11/70 that was extended to contain multiprocessing features. Up to four processors could be interconnected, although the physical cable management became unwieldy. Another variation on the 11/74 contained both the multiprocessing features and the Commercial Instruction Set. A substantial number of prototype 11/74s (of various types) were built and at least two multiprocessor systems were sent to customers for beta testing, but no systems were ever officially sold. A four processor system was maintained by the RSX-11 operating system development team for testing and a uniprocessor system served PDP-11 engineering for general purpose timesharing. The 11/74 was due to be introduced around the same time as the announcement of the new 32-bit product line and the first model: the VAX 11/780. The 11/74 was cancelled because of concern for its field maintainability, though employees believed the real reason was that it outperformed the 11/780 and would inhibit its sales. In any case, DEC never entirely migrated its PDP-11 customer base to the VAX. The primary reason was not performance, but the PDP-11's superior real-time responsiveness.PDP-11_item_4_32

Special-purpose versions PDP-11_section_15


  • GT40 – VT11 vector graphics terminal using a PDP-11/05.PDP-11_item_5_33
  • GT42 – VT11 vector graphics terminal using a PDP-11/10.PDP-11_item_5_34
  • GT44 – VT11 vector graphics terminal using a PDP-11/40.PDP-11_item_5_35
  • GT62 – VS60 vector graphics workstation using a PDP-11/34a and VT48 graphics processor.PDP-11_item_5_36
  • H11Heathkit OEM version of the LSI-11/03.PDP-11_item_5_37
  • VT20 – Terminal with PDP-11/05 with direct mapped character display for text editing and typesetting (predecessor of the VT71)PDP-11_item_5_38
  • VT71 – Terminal with LSI-11/03 and QBUS backplane with direct mapped character display for text editing and typesetting.PDP-11_item_5_39
  • VT103 – VT100 with backplane to host an LSI-11.PDP-11_item_5_40
  • VT173 – A high-end editing terminal containing an 11/03, which loaded its editing software over a serial connection to a host minicomputer. Used in various publishing environments, it was also offered with DECset, Digital's VAX/VMS 3.x native mode OEM version of the Datalogics Pager automated batch composition engine. When VT173 inventory was exhausted in 1985, Digital discontinued DECset and transferred its customer agreements to Datalogics. (HP now uses the name HP DECset for a software development toolset product.)PDP-11_item_5_41


  • MINC-11 – Laboratory system based on 11/03 or 11/23; when based on the 11/23, it was sold as a 'MINC-23', but many MINC-11 machines were field-upgraded with the 11/23 processor. Early versions of the MINC-specific software package would not run on the 11/23 processor because of subtle changes in the instruction set; MINC 1.2 is documented as compatible with the later processor.PDP-11_item_6_42
  • C.mmp – Multiprocessor system from Carnegie Mellon University.PDP-11_item_6_43


  • The Unimation robot arm controllers used Q-Bus LSI-11/73 systems with a DEC M8192 / KDJ11-A processor board and two DEC DLV11-J (M8043) async serial interface boards.PDP-11_item_7_44
  • SBC 11/21 (boardname KXT11) Falcon and Falcon Plus – single board computer on a Qbus card implementing the basic PDP-11 instruction set, based on T11 chipset containing 32 KB static RAM, two ROM sockets, three serial lines, 20 bit parallel I/O, three interval timers and a two-channel DMA controller. Up to 14 Falcons could be placed into one Qbus system.PDP-11_item_7_45
  • KXJ11 – QBUS card (M7616) with PDP-11 based peripheral processor and DMA controller. Based on a J11 CPU equipped with 512 kB RAM, 64 kB ROM and parallel and serial interfaces.PDP-11_item_7_46
  • HSC high end CI disk controllers used backplane mounted J11 and F11 processor cards to run their CHRONIC operating system.PDP-11_item_7_47
  • VAX Console – The DEC Professional Series PC-38N with a real-time interface (RTI) was used as the console for the VAX 8500 and 8550. The RTI has two serial line units: one connects to the VAX environmental monitoring module (EMM) and the other is a spare that could be used for data transfer. The RTI also has a programmable peripheral interface (PPI) consisting of three 8-bit ports for transferring data, address, and control signals between console and the VAX console interface.PDP-11_item_7_48

Unlicensed clones PDP-11_section_16

The PDP-11 was sufficiently popular that many unlicensed PDP-11-compatible minicomputers and microcomputers were produced in Eastern Bloc countries. PDP-11_sentence_103

Some were pin-compatible with the PDP-11 and could use its peripherals and system software. PDP-11_sentence_104

These include: PDP-11_sentence_105


  • SM-4, SM-1420, SM-1600, Electronika 100-25, Electronika BK series, Electronika 60, Electronika 85, DVK and UKNC (in the Soviet Union).PDP-11_item_8_49
  • SM-4, SM-1420, IZOT-1016 and peripherals (in Bulgaria).PDP-11_item_8_50
  • MERA-60 in Poland.PDP-11_item_8_51
  • SM-1620, SM-1630 (in East Germany).PDP-11_item_8_52
  • SM-4, TPA-1140, TPA-1148, TPA-11/440 (in Hungary).PDP-11_item_8_53
  • SM-4/20, SM 52-11, JPR-12R (in Czechoslovakia)PDP-11_item_8_54
  • CalData – Made in US, ran all DEC OSesPDP-11_item_8_55
  • the CORAL series (made at ICE Felix in Bucharest) and the INDEPENDENT series (made at ITC Timișoara) running the RSX-11M operating system (in Romania). The CORAL series had several models: the CORAL 4001 was roughly equivalent to the PDP-11/04, the CORAL 4011 was a PDP 11/34 clone, while the CORAL 4030 was a PDP-11/44 clone. These were used in public universities, originally operated with punched cards, later through video terminals like the Romanian DAF-2020, to teach FORTRAN and Pascal, until replaced by IBM PC compatibles, starting in 1991.PDP-11_item_8_56
  • Systime Computers models 1000, 3000, 5000 – OEM agreement for sales in the UK and Western Europe, but disputes originated over both intellectual property infringement and indirect sales to the Eastern Bloc.PDP-11_item_8_57

Operating systems PDP-11_section_17

Several operating systems were available for the PDP-11 PDP-11_sentence_106

From Digital PDP-11_section_18

From third parties PDP-11_section_19

Communications PDP-11_section_20

The DECSA communications server was a communications platform developed by DEC based on a PDP-11/24, with the provision for user installable I/O cards including asynchronous and synchronous modules. PDP-11_sentence_107

This product was used as one of the earliest commercial platforms upon which networking products could be built, including X.25 gateways, SNA gateways, routers, and terminal servers. PDP-11_sentence_108

Peripherals PDP-11_section_21

A wide range of peripherals were available; some of them were also used in other DEC systems like the PDP-8 or PDP-10. PDP-11_sentence_109

The following are some of the more common PDP-11 peripherals. PDP-11_sentence_110


Use PDP-11_section_22

The PDP-11 family of computers was used for many purposes. PDP-11_sentence_111

It was used as a standard minicomputer for general-purpose computing, such as timesharing, scientific, educational, medical, or business computing. PDP-11_sentence_112

Another common application was real-time process control and factory automation. PDP-11_sentence_113

Some OEM models were also frequently used as embedded systems to control complex systems like traffic-light systems, medical systems, numerical controlled machining, or for network-management. PDP-11_sentence_114

An example of such use of PDP-11s was the management of the packet switched network Datanet 1. PDP-11_sentence_115

In the 1980s, the UK's air traffic control radar processing was conducted on a PDP 11/34 system known as PRDS – Processed Radar Display System at RAF West Drayton. PDP-11_sentence_116

The software for the Therac-25 medical linear particle accelerator also ran on a 32K PDP 11/23. PDP-11_sentence_117

In 2013, it was reported that PDP-11 programmers would be needed to control nuclear power plants through 2050. PDP-11_sentence_118

Another use was for storage of test programs for Teradyne ATE equipment, in a system known as the TSD (Test System Director). PDP-11_sentence_119

As such, they were in use until their software was rendered inoperable by the Year 2000 problem. PDP-11_sentence_120

The US Navy used a PDP-11/34 to control its Multi-station Spatial Disorientation Device, a simulator used in pilot training, until 2007, when it was replaced by a PC-based emulator that could run the original PDP-11 software and interface with custom Unibus controller cards. PDP-11_sentence_121

A PDP-11/45 was used for the experiment that discovered the J/ψ meson at the Brookhaven National Laboratory. PDP-11_sentence_122

In 1976, Samuel C. C. Ting received the Nobel Prize for this discovery. PDP-11_sentence_123

Emulators PDP-11_section_23

Ersatz-11 PDP-11_section_24

Ersatz-11, a product of D Bit, emulates the PDP-11 instruction set running under DOS, OS/2, Windows, Linux or stand-alone (no OS). PDP-11_sentence_124

It can be used to run RSTS or other PDP-11 operating systems. PDP-11_sentence_125

SimH PDP-11_section_25

SimH is an emulator that compiles and runs on a number of platforms (including Linux) and supports hardware emulation for the DEC PDP-1, PDP-8, PDP-10, PDP-11, VAX, AltairZ80, several IBM mainframes, and other minicomputers. PDP-11_sentence_126

See also PDP-11_section_26


  • Heathkit H11, a 1977 Heathkit personal computer based on the PDP-11PDP-11_item_10_71
  • MACRO-11, the PDP-11's native assembly languagePDP-11_item_10_72
  • PL-11, a high-level assembler for the PDP-11 written at CERNPDP-11_item_10_73
  • SIMH, a multiple minicomputer architecture emulator written in portable CPDP-11_item_10_74

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/PDP-11.