The PDP-11 is a series of

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two ...

minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ' ...

s sold by

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president un ...

(DEC) from 1970 into the 1990s, one of a set of products in the

Programmed Data Processor Programmed Data Processor (PDP), referred to by some customers, media and authors as "Programmable Data Processor," is a term used by the Digital Equipment Corporation from 1957 to 1990 for several lines of minicomputers. The name 'PDP' i ...

(PDP) series. In total, around 600,000 PDP-11s of all models were sold, making it one of DEC's most successful product lines. The PDP-11 is considered by some experts to be the most popular minicomputer. The PDP-11 included a number of innovative features in its

instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...

and additional general-purpose registers that made it much easier to program than earlier models in the PDP series. Further, the innovative

Unibus The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon ...

system allowed external devices to be easily interfaced to the system using

direct memory access Direct memory access (DMA) is a feature of computer systems and allows certain hardware subsystems to access main system memory independently of the central processing unit (CPU). Without DMA, when the CPU is using programmed input/output, it is ...

, opening the system to a wide variety of

peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...

s. The PDP-11 replaced the

PDP-8 The PDP-8 is a 12-bit minicomputer that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units being sold over the model's lifetime. Its basic design follows the pioneer ...

in many

real-time computing Real-time computing (RTC) is the computer science term for hardware and software systems subject to a "real-time constraint", for example from event to system response. Real-time programs must guarantee response within specified time constrai ...

applications, although both product lines lived in parallel for more than 10 years. The ease of programming of the PDP-11 made it very popular for general-purpose computing uses also. The design of the PDP-11 inspired the design of late-1970s

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

s including the

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 ser ...

x86 and the

Motorola 68000 The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Secto ...

. 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 CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initi ...

and hence also

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few o ...

. The first officially named version of

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, ...

ran on the PDP-11/20 in 1970. It is commonly stated that the

C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language, as well a ...

took advantage of several low-level PDP-11–dependent programming features, albeit not originally by design. An effort to expand the PDP-11 from 16 to 32-bit addressing led to the

VAX-11 The VAX-11 is a discontinued family of 32-bit superminicomputers, running the Virtual Address eXtension (VAX) instruction set architecture (ISA), developed and manufactured by Digital Equipment Corporation (DEC). Development began in 1976. In a ...

design, which took part of its name from the PDP-11.

History

Previous machines

In 1963, DEC introduced what is considered to be the first commercial minicomputer in the form of the

PDP-5 The PDP-5 was Digital Equipment Corporation's first 12-bit computer, introduced in 1963. History An earlier 12-bit computer, named LINC has been described as the first minicomputer and also "the first modern personal computer." It had 2,048 12- ...

. This was a 12-bit design adapted from the 1962

LINC The LINC (Laboratory INstrument Computer) is a 12-bit, 2048-word transistorized computer. The LINC is considered by some the first minicomputer and a forerunner to the personal computer. Originally named the "Linc", suggesting the project's or ...

machine that was intended to be used in a lab setting. 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 The PDP-4 was the successor to the Digital Equipment Corporation's PDP-1. History This 18-bit machine, first shipped in 1962, was a compromise: "with slower memory and different packaging" than the PDP-1, but priced at $65,000 - less than half th ...

. The PDP-5 was a success, ultimately selling about 1,000 machines. This led to the

, a further cost-reduced 12-bit model that was even more successful, selling about 50,000 units. During this period, the computer market was moving from

computer word In computing, a word is the natural unit of data used by a particular processor design. A word is a fixed-sized datum handled as a unit by the instruction set or the hardware of the processor. The number of bits or digits in a word (the ''word s ...

lengths based on units of 6 bits to units of 8 bits, following the introduction of the 7-bit

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...

standard. 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. This prompted several of the engineers from the PDP-X program to leave DEC and form

Data General Data General Corporation was one of the first minicomputer firms of the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation (DEC). Their first product, 1969's Data General Nova, was a 16-bit minicompute ...

. The next year they introduced the 16-bit

Data General Nova The Data General Nova is a series of 16-bit minicomputers released by the American company Data General. The Nova family was very popular in the 1970s and ultimately sold tens of thousands of units. The first model, known simply as "Nova", was ...

. 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.

Release

Ken Olsen Kenneth Harry "Ken" Olsen (February 20, 1926 – February 6, 2011) was an American engineer who co-founded Digital Equipment Corporation (DEC) in 1957 with colleague Harlan Anderson and his brother Stan Olsen. Background Kenneth Harry Olsen w ...

was more interested in a small 8-bit machine than the larger 16-bit system. This became the "Desk Calculator" project. Not long after,

Datamation ''Datamation'' is a computer magazine that was published in print form in the United States between 1957 and 1998,

published a note about a desk calculator being developed at DEC, which caused concern at

Wang Laboratories Wang Laboratories was a US computer company founded in 1951 by An Wang and G. Y. Chu. The company was successively headquartered in Cambridge, Massachusetts (1954–1963), Tewksbury, Massachusetts (1963–1976), and finally in Lowell, Massachus ...

, who were heavily invested in that market. Before long, it became clear that the entire market was moving to 16-bit, and the Desk Calculator began a 16-bit design as well. The team decided that the best approach to a new architecture would be to minimize the memory bandwidth needed to execute the instructions. Larry McGowan coded up a series of

assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence b ...

programs using the instruction sets of various existing platforms and examined how much memory would be exchanged to execute them. Harold McFarland joined the effort and had already written a very complex instruction set that the team rejected, but a second one was simpler and would ultimately form the basis for the PDP-11. When they first presented the new architecture, the managers were dismayed. It lacked immediate data and short addresses, both of which were considered essential to improving memory performance. McGowan and McFarland were eventually able to convince them that the system would work as expected, and suddenly "the Desk Calculator project got hot". Much of the system was developed using a

PDP-10 Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, espec ...

where the SIM-11 simulated what would become the PDP-11/20 and Bob Bowers wrote an assembler for it. One late change was that the marketing team wanted to ship the minimal configuration with 2 K of memory, but when McGowan stated this would mean an assembler could not run on it the minimum was expanded to 4 K. They also wanted to use the forward slash character for comments in the assembler code, like the PDP-8, but McGowan stated that he would then have to use semicolon for division and that was dropped. The PDP-11 family was announced in January 1970 and shipments began early that year. DEC sold over 170,000 PDP-11s in the 1970s.Paul Cerruzi, ''A History of Modern Computing'', MIT Press, 2003, , page 199 Initially manufactured of small-scale

transistor–transistor logic Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors. Its name signifies that transistors perform both the logic function (the first "transistor") and the amplifying function (the second "transistor"), as o ...

, a single-board

large scale integration An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tin ...

version of the processor was developed in 1975. A two-or-three-chip processor, the J-11 was developed in 1979. The last models of the PDP-11 line were the PDP-11/94 and PDP-11/93 introduced in 1990.

Innovative features

Instruction set orthogonality

The PDP-11 processor architecture has a mostly

orthogonal instruction set In computer engineering, an orthogonal instruction set is an instruction set architecture where all instruction types can use all addressing modes. It is "orthogonal" in the sense that the instruction type and the addressing mode vary independentl ...

. 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. There are no specific ''input'' or ''output'' instructions; the PDP-11 uses

memory-mapped I/O Memory-mapped I/O (MMIO) and port-mapped I/O (PMIO) are two complementary methods of performing input/output (I/O) between the central processing unit (CPU) and peripheral devices in a computer. An alternative approach is using dedicated I/O pr ...

and so the same ''move'' instruction is used; orthogonality even enables moving data directly from an input device to an output device. More complex instructions such as ''add'' likewise can have memory, register, input, or output as source or destination. Most operands can apply any of eight addressing modes to eight registers. 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). Use of relative addressing lets a machine-language program be position-independent.

No dedicated I/O instructions

Early models of the PDP-11 had no dedicated

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...

for

input/output In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals ...

, but only a

system bus A system bus is a single computer bus that connects the major components of a computer system, combining the functions of a data bus to carry information, an address bus to determine where it should be sent or read from, and a control bus to det ...

called the

, as input and output devices were mapped to memory addresses. An input/output device determined the memory addresses to which it would respond, and specified its own

interrupt vector An interrupt vector table (IVT) is a data structure that associates a list of interrupt handlers with a list of interrupt requests in a table of interrupt vectors. Each entry of the interrupt vector table, called an interrupt vector, is the addre ...

and interrupt priority. 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. DEC openly published the basic Unibus specifications, even offering prototyping bus interface circuit boards, and encouraging customers to develop their own Unibus-compatible hardware. The Unibus made the PDP-11 suitable for custom peripherals. One of the predecessors of

Alcatel-Lucent Alcatel–Lucent S.A. () was a French–American global telecommunications equipment company, headquartered in Boulogne-Billancourt, France. It was formed in 2006 by the merger of France-based Alcatel and U.S.-based Lucent, the latter being a su ...

, the

Bell Telephone Manufacturing Company The International Bell Telephone Company (IBTC) of Brussels, Belgium, was created in 1879 by the Bell Telephone Company of Boston, Massachusetts, a precursor entity to the American Telephone and Telegraph Company (AT&T), initially to sell imported ...

, developed the BTMC DPS-1500 packet-switching (

X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts a ...

) network and used PDP-11s in the regional and national network management system, with the Unibus directly connected to the DPS-1500 hardware. Higher-performance members of the PDP-11 family departed from the single-bus approach. The PDP-11/45 had a dedicated data path within the

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...

, connecting semiconductor memory to the processor, with core memory and I/O devices connected via the Unibus. 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 The Massbus is a high-performance computer input/output bus designed in the 1970s by Digital Equipment Corporation (DEC). The architecture development was sponsored by Gordon Bell and John Levy was the principal architect. The bus was used by Di ...

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

Interrupts

The PDP-11 supports hardware

interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, ...

s at four priority levels. Interrupts are serviced by software service routines, which could specify whether they themselves could be interrupted (achieving interrupt nesting). 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. 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. 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. The article on PDP-11 architecture provides more details on interrupts.

Designed for mass production

The PDP-11 was designed for ease of manufacture by semiskilled labor. The dimensions of its pieces were relatively non-critical. It used a wire-wrapped

backplane A backplane (or "backplane system") is a group of electrical connectors in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus. It is used as a backbo ...

LSI-11

The LSI-11 (PDP-11/03), introduced in February 1975 is the first PDP-11 model produced using

large-scale integration An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

; the entire CPU is contained on four LSI chips made by

Western Digital Western Digital Corporation (WDC, commonly known as Western Digital or WD) is an American computer drive manufacturer and data storage company, headquartered in San Jose, California. It designs, manufactures and sells data technology produ ...

(the

MCP-1600 The MCP-1600 is a multi-chip 16-bit microprocessor introduced by Western Digital in 1975 and produced through the early 1980s. Used in the Pascal MicroEngine, the WD16 processor in the Alpha Microsystems AM-100, and the DEC LSI-11 microcomput ...

chip set; a fifth chip can be added to extend the instruction set). It uses a bus which is a close variant of the Unibus called the LSI Bus or

Q-Bus The Q-bus,Schmidt, Atlant G.,Unibus,Q-Bus and VAXBI Bus, in ''Digital bus handbook'', Di Giacomo Joseph Ed., McGraw Hill, 1990 also known as the LSI-11 Bus, is one of several bus technologies used with PDP and MicroVAX computer systems previo ...

; 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. 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). The CPU

microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a la ...

includes a

debugger A debugger or debugging tool is a computer program used to test and debug other programs (the "target" program). The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its executi ...

: firmware with a direct serial interface (

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' ('' data terminal equipment'') suc ...

current loop In electrical signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time. A major application of current loops is the industry d ...

) to a

terminal Terminal may refer to: Computing Hardware * Terminal (electronics), a device for joining electrical circuits together * Terminal (telecommunication), a device communicating over a line * Computer terminal, a set of primary input and output devi ...

. This lets the operator do

debugging In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve i ...

by typing commands and reading

octal The octal numeral system, or oct for short, is the radix, base-8 number system, and uses the Numerical digit, digits 0 to 7. This is to say that 10octal represents eight and 100octal represents sixty-four. However, English, like most languages, ...

numbers, rather than operating switches and reading lights, the typical debugging method at the time. 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). The operator can also specify which disk to

boot A boot is a type of footwear. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is c ...

from. Both innovations increased the reliability and decreased the cost of the LSI-11. 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. Later PDP-11 Unibus systems were designed to use similar Q-Bus processor cards, using a Unibus adapter to support existing Unibus

s, sometimes with a special memory bus for improved speed. There were other significant innovations in the Q-Bus lineup. For example, a system variant of the PDP-11/03 introduced full system

power-on self-test A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on. This article mainly deals with POSTs on personal computers, but many other embed ...

(POST). File:PDP-11-M7270.jpg, Q-Bus board with LSI-11/2 CPU File:KL DEC F11.jpg, DEC "Fonz-11" (F11) Chipset File:KL DEC J11.jpg, DEC "Jaws-11" (J11) Chipset

Decline

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

throughput Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered ove ...

of the Unibus and Q-Bus started to become a system-performance

bottleneck Bottleneck literally refers to the narrowed portion (neck) of a bottle near its opening, which limit the rate of outflow, and may describe any object of a similar shape. The literal neck of a bottle was originally used to play what is now known as ...

, and the 16-bit logical address limitation hampered the development of larger software applications. The article on PDP-11 architecture describes the hardware and software techniques used to work around address-space limitations. 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 In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence ...

market. 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 The MicroVAX is a discontinued family of low-cost minicomputers developed and manufactured by Digital Equipment Corporation (DEC). The first model, the MicroVAX I, was introduced in 1983.(announced October 1983) They used processors that implemen ...

. For a decade, the PDP-11 was the smallest system that could run

, but in the 1980s, the

IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...

and its clones largely took over the small computer market; ''

BYTE The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...

'' in 1984 reported that the PC's

Intel 8088 The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and ...

microprocessor could outperform the PDP-11/23 when running Unix. Newer microprocessors such as the

(1979) and

Intel 80386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistors workstation A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating systems. The term ''workst ...

s that would often run Unix variants. These included the

HP 9000 HP 9000 is a line of workstation and server computer systems produced by the Hewlett-Packard (HP) Company. The native operating system for almost all HP 9000 systems is HP-UX, which is based on UNIX System V. The HP 9000 brand was introduced ...

series 200 (starting with the HP 9826A in 1981) and 300/400, with the

HP-UX HP-UX (from "Hewlett Packard Unix") is Hewlett Packard Enterprise's proprietary implementation of the Unix operating system, based on Unix System V (initially System III) and first released in 1984. Current versions support HPE Integrity Se ...

system being ported to the 68000 in 1984;

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, t ...

workstations running

SunOS SunOS is a Unix-branded operating system developed by Sun Microsystems for their workstation and server computer systems. The ''SunOS'' name is usually only used to refer to versions 1.0 to 4.1.4, which were based on BSD, while versions 5.0 an ...

, starting with the Sun-1 in 1982;

Apollo/Domain Apollo/Domain was a range of workstations developed and produced by Apollo Computer from circa 1980 to 1989. The machines were built around the Motorola 68k family of processors, except for the DN10000, which had from one to four of Apollo's RIS ...

workstations starting with the DN100 in 1981 running

Domain/OS Domain/OS is the discontinued operating system used by the Apollo/Domain line of workstations manufactured by Apollo Computer. It was originally launched in 1981 as AEGIS, and was rebranded to Domain/OS in 1988 when Unix environments were added to ...

, which was proprietary but offered a degree of Unix compatibility; and the

Silicon Graphics Silicon Graphics, Inc. (stylized as SiliconGraphics before 1999, later rebranded SGI, historically known as Silicon Graphics Computer Systems or SGCS) was an American high-performance computing manufacturer, producing computer hardware and soft ...

IRIS Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...

range, which developed into Unix-based workstations by 1985 (IRIS 2000). Personal computers based on the 68000 like the

Apple Lisa Lisa is a desktop computer developed by Apple, released on January 19, 1983. It is one of the first personal computers to present a graphical user interface (GUI) in a machine aimed at individual business users. Its development began in 1978. ...

and

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...

or the

Commodore Amiga Amiga is a family of personal computers introduced by Commodore in 1985. The original model is one of a number of mid-1980s computers with 16- or 32-bit processors, 256 KB or more of RAM, mouse-based GUIs, and significantly improved graphi ...

arguably constituted less of a threat to DEC's business, although technically these systems could also run Unix derivatives. In the early years, in particular,

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...

Xenix Xenix is a discontinued version of the Unix operating system for various microcomputer platforms, licensed by Microsoft from AT&T Corporation in the late 1970s. The Santa Cruz Operation (SCO) later acquired exclusive rights to the software, ...

was ported to systems like the

TRS-80 Model 16 The TRS-80 Model II is a computer system launched by Tandy in October 1979, and targeted at the small-business market. It is not an upgrade of the original TRS-80 Model I, but a new system. The Model II was succeeded by the compatible TRS-80 Mo ...

(with up to 1 MB of memory) in 1983, and to the Apple Lisa, with up to 2 MB of installed RAM, in 1984. The mass-production of those chips eliminated any cost advantage for the 16-bit PDP-11. 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. 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. For several years, Mentec produced new PDP-11 processors. Other companies found a

niche market A niche market is the subset of the market on which a specific product is focused. The market niche defines the product features aimed at satisfying specific market needs, as well as the price range, production quality and the demographics that i ...

for replacements for legacy PDP-11 processors, disk subsystems, etc. At the same time, free implementations of Unix for the PC based on BSD or

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...

became available. 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.

Models

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. Within each group, most models were offered in two versions, one intended for OEMs and one intended for end-users. Although all models share the same instruction set, later models added new instructions and interpreted certain instructions slightly differently. As the architecture evolved, there were also variations in handling of some processor status and control registers.

Unibus models

The following models use the Unibus as their principal bus: * 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 In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can ...

is supported by

options using various data formats. The 11/20 lacks any kind of

memory protection Memory protection is a way to control memory access rights on a computer, and is a part of most modern instruction set architectures and operating systems. The main purpose of memory protection is to prevent a process from accessing memory that h ...

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-11/45 (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 Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

; support memory mapping and protection. First model to support an optional FP11 floating-point

coprocessor A coprocessor is a computer processor used to supplement the functions of the primary processor (the CPU). Operations performed by the coprocessor may be floating-point arithmetic, graphics, signal processing, string processing, cryptography or I ...

, which established the format used in later models. * 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-11/05 and PDP-11/10 – 1972. A cost-reduced successor to the PDP-11/20. DEC Datasystem 350 models from 1975 include the PDP-11/10. * 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-11/34 (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 In computing, a cache ( ) is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewher ...

option. * PDP-11/60 – 1977. A PDP-11 with user-writable microcontrol store; this was designed by another team led by Jim O'Loughlin. * PDP-11/44 – 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 gate A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic ga ...

s; later models were all microprocessor-based. It was also the last PDP-11 architecture created by

, later models were VLSI chip realizations of the existing system architectures. * PDP-11/24 – 1979. First VLSI PDP-11 for Unibus, using the "Fonz-11" (F11) chip set with a Unibus adapter. * PDP-11/84 – 1985-1986. Using the VLSI "Jaws-11" (J11) chip set with a Unibus adapter. * PDP-11/94 – 1990. J11-based, faster than 11/84.

Q-bus models

The following models use the Q-Bus as their principal bus: * PDP-11/03 (also known as the LSI-11/03) – The first PDP-11 implemented with

ICs, this system uses a four-package

chipset from Western Digital and supports 60 kB of memory. * – Second generation of LSI (F-11). Early units supported only 248 kB of memory. * 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. * 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. * MicroPDP-11/53 – Slower 11/73 with on-board memory. * MicroPDP-11/83 – Faster 11/73 with PMI (private memory interconnect). * MicroPDP-11/93 – Faster 11/83; final DEC Q-Bus PDP-11 model. * KXJ11 – Q-Bus 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. * 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. * 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 Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globa ...

. * Mentec M1 – Processor upgrade board; microcode implementation of PDP-11 instruction set by Mentec, using

Atmel Atmel Corporation was a creator and manufacturer of semiconductors before being subsumed by Microchip Technology in 2016. Atmel was founded in 1984. The company focused on embedded systems built around microcontrollers. Its products included mi ...

0.35

μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...

ASIC An application-specific integrated circuit (ASIC ) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficie ...

. * Quickware QED-993 – High performance PDP-11/93 processor upgrade board. * DECserver 500 and 550 LAT terminal servers DSRVS-BA using the KDJ11-SB chipset

Models without standard bus

* PDT-11/110 * PDT-11/130 * PDT-11/150 The PDT series were desktop systems marketed as "smart terminals". The /110 and /130 were housed in a

VT100 The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special ...

terminal enclosure. 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. 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. The /150 in combination with a VT105 terminal was also sold as MiniMINC, a budget version of the MINC-11. * PRO-325 * PRO-350 * PRO-380 The DEC Professional series are desktop PCs intended to compete with IBM's earlier

8088 The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers a ...

and

80286 The Intel 80286 (also marketed as the iAPX 286 and often called Intel 286) is a 16-bit microprocessor that was introduced on February 1, 1982. It was the first 8086-based CPU with separate, non- multiplexed address and data buses and also the ...

based personal computers. The models are equipped with 5 inch floppy disk drives and hard disks, except the 325 which has no hard disk. The original operating system was P/OS, which was essentially

RSX-11 RSX-11 is a discontinued family of multi-user real-time operating systems for PDP-11 computers created by Digital Equipment Corporation. In widespread use through the late 1970s and early 1980s, RSX-11 was influential in the development of later ...

M+ with a menu system on top. As the design was intended to avoid software exchange with existing PDP-11 models, the poor market response was unsurprising. The

RT-11 RT-11 (Real-time 11) is a discontinued small, low-end, single-user real-time operating system for the full line of Digital Equipment Corporation PDP-11 16-bit computers. RT-11 was first implemented in 1970. It was widely used for real-time computin ...

operating system was eventually ported to the PRO series. A port of

RSTS/E RSTS () is a multi-user time-sharing operating system developed by Digital Equipment Corporation (DEC, now part of Hewlett-Packard) for the PDP-11 series of 16-bit minicomputers. The first version of RSTS (RSTS-11, Version 1) was implemented in 1 ...

to the PRO series was also done internal to DEC, but it was not released. 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. 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.

Models that were planned but never introduced

* PDP-11/27 – A Jaws-11 implementation that would have used the VAXBI Bus as its principal I/O bus. * PDP-11/68 – A follow-on to the PDP-11/60 that would have supported 4 MB of physical memory. * 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 A uniprocessor system is defined as a computer system that has a single central processing unit that is used to execute computer tasks. As more and more modern software is able to make use of multiprocessing architectures, such as SMP and MPP, t ...

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.

Special-purpose versions

* GT40 – VT11

vector graphics Vector graphics is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector display ...

terminal using a PDP-11/10. * GT42 – VT11 vector graphics terminal using a PDP-11/10. * GT44 – VT11 vector graphics terminal using a PDP-11/40. * GT62 – VS60 vector graphics workstation using a PDP-11/34a and VT48 graphics processor. * H11 –

Heathkit Heathkit is the brand name of kits and other electronic products produced and marketed by the Heath Company. The products over the decades have included electronic test equipment, high fidelity home audio equipment, television receivers, amateu ...

OEM version of the LSI-11/03. * VT20 – Terminal with PDP-11/05 with direct mapped character display for text editing and typesetting (predecessor of the VT71) * VT71 – Terminal with LSI-11/03 and Q-Bus backplane with direct mapped character display for text editing and typesetting. *

VT103 The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special f ...

– VT100 with backplane to host an LSI-11. * 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 Datalogics is a computer software company formed in 1967 and based in Chicago, IL. The company licenses software development kits for working with PDF and other document file types. They have previously developed their own typesetting and datab ...

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.) * 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. *

C.mmp The C.mmp was an early ''multiple instruction, multiple data'' ( MIMD) multiprocessor system developed at Carnegie Mellon University (CMU) by William Wulf (1971). The notation ''C.mmp'' came from the PMS notation of Gordon Bell and Allen Newell ...

– Multiprocessor system from

Carnegie Mellon University Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...

* The

Unimation Unimation was the world's first robotics company. It was founded in 1962 by Joseph F. Engelberger and George Devol and was located in Danbury, Connecticut. Devol had already applied for a patent an industrial robotic arm in 1954; was issued in ...

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. * SBC 11/21 (boardname KXT11) Falcon and Falcon Plus – single board computer on a Q-Bus 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 Q-Bus system. * KXJ11 – Q-Bus 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. * HSC high end CI disk controllers used backplane mounted J11 and F11 processor cards to run their CHRONIC operating system. * 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.

Unlicensed clones

The PDP-11 was sufficiently popular that many unlicensed PDP-11-compatible minicomputers and microcomputers were produced in

Eastern Bloc The Eastern Bloc, also known as the Communist Bloc and the Soviet Bloc, was the group of socialist states of Central and Eastern Europe, East Asia, Southeast Asia, Africa, and Latin America under the influence of the Soviet Union that existed du ...

countries. Some were pin-compatible with the PDP-11 and could use its peripherals and system software. These include: *

SM-4 The SM-4 (CM-4) is a PDP-11/40 compatible system, manufactured in the Eastern Bloc in the 1980s. It was very popular in science and technology. They were manufactured in the Soviet Union, Bulgaria and Hungary, beginning in 1975. The standard con ...

SM-1420 The SM-1420 (CM-1420) is a 16 bit DEC PDP-11/45 minicomputer clone, and the successor to SM-4 in Soviet Bloc countries. Under the direction of Minpribor it was produced in the Soviet Union and Bulgaria from 1983 onwards, and is more than twice as f ...

, SM-1600, Electronika 100-25, Electronika BK series, Electronika 60, Electronika 85,

DVK DVK (russian: ДВК, Диалоговый вычислительный комплекс, ''Interactive Computing Complex'') is a Soviet PDP-11-compatible personal computer. Overview The design is also known as Elektronika MS-0501 and Elektronika ...

UKNC UKNC (russian: УКНЦ) is a Soviet PDP-11-compatible educational micro computer, aimed at teaching school informatics courses. It is also known as Elektronika MS-0511. UKNC stands for Educational Computer by Scientific Centre. Hardware *CPU: KM ...

, and some models of the

SM EVM SM EVM (СМ ЭВМ, abbreviation of Система Малых ЭВМ—literally System of Mini Computers) are several types of Soviet Union, Soviet and Comecon minicomputers produced from 1975 through the 1980s. Most types of SM EVM are clone (co ...

series (in the

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...

). *

, IZOT-1016 and peripherals (in

Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedo ...

). * MERA-60 in

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...

. * SM-1620, SM-1630 (in

East Germany East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a country that existed from its creation on 7 October 1949 until German reunification, its dissolution on 3 October 1990. In t ...

). *

, TPA-1140, TPA-1148, TPA-11/440 (in

Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Cr ...

). * SM-4/20, SM 52-11, JPR-12R (in Czechoslovakia) * CalData – Made in US, ran all DEC OSes * the CORAL series (made at

ICE Felix Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...

Bucharest Bucharest ( , ; ro, București ) is the capital and largest city of Romania, as well as its cultural, industrial, and financial centre. It is located in the southeast of the country, on the banks of the Dâmbovița River, less than north o ...

) and the

INDEPENDENT Independent or Independents may refer to: Arts, entertainment, and media Artist groups * Independents (artist group), a group of modernist painters based in the New Hope, Pennsylvania, area of the United States during the early 1930s * Independe ...

series (made at ITC

Timișoara ), City of Roses ( ro, Orașul florilor), City of Parks ( ro, Orașul parcurilor) , image_map = Timisoara jud Timis.svg , map_caption = Location in Timiș County , pushpin_map = Romania#Europe , pushpin_ ...

) running the RSX-11M operating system (in

Romania Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...

). 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 state-owned companies and in public universities, originally operated with

punched card A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...

s, later through video terminals like the Romanian DAF-2020, to teach FORTRAN and Pascal, until replaced by IBM PC compatibles, starting in 1991. *

Systime Computers Systime Computers Ltd was a British computer manufacturer and systems integrator of the 1970s and 1980s. During the late 1970s and early 1980s, Systime become the second largest British manufacturer of computers, specializing in the minicompu ...

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

Operating systems

Several

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s were available for the PDP-11

From Digital

* Commercial Operating System * BATCH-11/DOS-11 * CAPS-11 (Cassette Programming System) * CHRONIC Hierarchical Storage Controller executive * GAMMA-11 * DSM-11 * IAS * P/OS *

* TRAX (Transaction Processing system) *

Ultrix Ultrix (officially all-caps ULTRIX) is the brand name of Digital Equipment Corporation's (DEC) discontinued native Unix operating systems for the PDP-11, VAX, MicroVAX and DECstations. History The initial development of Unix occurred on DEC eq ...

-11

From third parties

* ANDOS *

CSI-DOS CSI-DOS is an operating system, created in Samara, for the Soviet Elektronika BK-0011M and Elektronika BK-0011 microcomputers. CSI-DOS did not support the earlier BK-0010. CSI-DOS used its own unique file system and only supported a color graph ...

DEIMOS Deimos, a Greek word for ''dread'', may refer to: * Deimos (deity), one of the sons of Ares and Aphrodite in Greek mythology * Deimos (moon), the smaller and outermost of Mars' two natural satellites * Elecnor Deimos, a Spanish aerospace company * ...

(University of Edinburgh) *

DEMOS Demos may refer to: Computing * DEMOS, a Soviet Unix-like operating system * DEMOS (ISP), the first internet service provider in the USSR * Demos Commander, an Orthodox File Manager for Unix-like systems * plural for Demo (computer programming) ...

(Soviet Union) *

Duress Coercion () is compelling a party to act in an involuntary manner by the use of threats, including threats to use force against a party. It involves a set of forceful actions which violate the free will of an individual in order to induce a desi ...

(

University of Illinois at Urbana–Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Un ...

) * LOS/C, a small unitasking system written by BRL for the BRL routers and the I/O controller for the Denelcor HEP * MERT * Micropower Pascal * MK-DOS *

MONECS MONECS ( Monash University Educational Computing System) was a computer operating system with BASIC, COBOL, FORTRAN, Pascal interpreters, plus machine language facility. Specifically designed for computer science education in Australian seconda ...

* MTS (Multi-Tasking System written in RTL/2 by SPL) *

MUMPS MUMPS ("Massachusetts General Hospital Utility Multi-Programming System"), or M, is an imperative, high-level programming language with an integrated transaction processing key–value database. It was originally developed at Massachusetts Gene ...

* MUSS-11 * PC11 (Decus 11-501/

Pilkington Pilkington is a Japanese-owned glass-manufacturing company which is based in Lathom, Lancashire, United Kingdom. In the UK it includes several legal entities and is a subsidiary of Japanese company NSG Group. Prior to its acquisition by NSG ...

) * polyForth, Forth Inc.'s

Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotla ...

for the PDP-11 * ROSTTP (Realtime Operating System for Terminal Teletype Processing/Simpact) * SHAREeleven, SHAREplus * Solo by Per Brinch Hansen *

Sphere A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the c ...

(Infosphere – Portland Oregon 1981–87) * Softech Microsystems UCSD System with

UCSD Pascal UCSD Pascal is a Pascal programming language system that runs on the UCSD p-System, a portable, highly machine-independent operating system. UCSD Pascal was first released in 1977. It was developed at the University of California, San Diego (U ...

TRIPOS At the University of Cambridge, a Tripos (, plural 'Triposes') is any of the examinations that qualify an undergraduate for a bachelor's degree or the courses taken by a student to prepare for these. For example, an undergraduate studying mat ...

* TSX-Plus *

(many versions, including

Version 6 Unix Sixth Edition Unix, also called Version 6 Unix or just V6, was the first version of the Unix operating system to see wide release outside Bell Labs. It was released in May 1975 and, like its direct predecessor, targeted the DEC PDP-11 family of ...

Version 7 Unix Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercial ...

, UNIX System III, and

2BSD The History of the Berkeley Software Distribution begins in the 1970s. 1BSD (PDP-11) The earliest distributions of Unix from Bell Labs in the 1970s included the source code to the operating system, allowing researchers at universities to modify an ...

) *

Xinu Xinu Is Not Unix (Xinu, a recursive acronym), is an operating system for embedded systems, originally developed by Douglas Comer for educational use at Purdue University in the 1980s. The name is both recursive, and is '' Unix'' spelled backwa ...

OS for instructional purposes *

Venix Venix is a discontinued version of the Unix operating system for low-end computers, developed by VenturCom, a "company that specialises in the skinniest implementations of Unix".VenturCom ships real-time Venix/386. Computer Business Review, 1 Feb ...

(implementation/port of Unix developed by

VenturCom Ardence was a software company headquartered in Waltham, Massachusetts with representatives in Washington, D.C.; Virginia Beach, VA; Chicago, IL; Denton, TX; and in Europe, the Middle East, Africa and India. It developed a software-streaming prod ...

)

Communications

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. 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 server A terminal server connects devices with a serial port to a local area network (LAN). Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication ...

s. Ethernet adaptors, such as the DEQNA

card, were also available. Many of the earliest systems on the

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...

were PDP-11's

Peripherals

A wide range of peripherals were available; some of them were also used in other DEC systems like the

. The following are some of the more common PDP-11 peripherals. * CR11 –

reader * DL11 – single serial line for either

* LA30/LA36 –

DECwriter The DECwriter series was a family of computer terminals from Digital Equipment Corporation (DEC). They were typically used in a fashion similar to a teletype, with a computer output being printed to paper and the user inputting information on the ...

dot-matrix printing keyboard terminal * LP11 – high speed

line printer A line printer prints one entire line of text before advancing to another line. Most early line printers were impact printers. Line printers are mostly associated with unit record equipment and the early days of digital computing, but the ...

* PC11 – high speed papertape reader/punch * RA, RD series – fixed platter

hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magn ...

* RK series – hard disk with exchangeable platter * RL01/RL02 – hard disk with exchangeable platter * RM, RP series – exchangeable multi-platter hard disk * RX01/RX02 – 8-inch

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined ...

* RX50/RX33 – 5.25 floppy disk * TU10 –

9 track tape 9 (nine) is the natural number following and preceding . Evolution of the Arabic digit In the beginning, various Indians wrote a digit 9 similar in shape to the modern closing question mark without the bottom dot. The Kshatrapa, Andhra and ...

drive * TU56 –

DECtape DECtape, originally called Microtape, is a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VA ...

block-addressed tape system * VT05/VT50/ VT52/

– video display terminal

Use

The PDP-11 family of computers was used for many purposes. It was used as a standard minicomputer for general-purpose computing, such as

timesharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence ...

, scientific, educational, medical, or business computing. Another common application was

real-time Real-time or real time describes various operations in computing or other processes that must guarantee response times within a specified time (deadline), usually a relatively short time. A real-time process is generally one that happens in defined ...

process control An industrial process control in continuous production processes is a discipline that uses industrial control systems to achieve a production level of consistency, economy and safety which could not be achieved purely by human manual control. ...

and

factory automation Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...

. Some OEM models were also frequently used as

embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded ...

s to control complex systems like traffic-light systems, medical systems,

numerical control Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes ...

led

machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

, or for network-management. An example of such use of PDP-11s was the management of the packet switched network

Datanet DataNet, or Sustainable Digital Data Preservation and Access Network Partner was a research program of the U.S. National Science Foundation Office of Cyberinfrastructure. The office announced a request for proposals with this title on September 28 ...

1. In the 1980s, the UK's

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airsp ...

radar processing was conducted on a PDP 11/34 system known as PRDS – Processed Radar Display System at RAF West Drayton. The software for the

Therac-25 The Therac-25 was a computer-controlled radiation therapy machine produced by Atomic Energy of Canada Limited (AECL) in 1982 after the Therac-6 and Therac-20 units (the earlier units had been produced in partnership with of France). It was invo ...

medical

linear particle accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear b ...

also ran on a 32K PDP 11/23. In 2013, it was reported that PDP-11 programmers would be needed to control nuclear power plants through 2050. Another use was for storage of test programs for

Teradyne Teradyne, Inc. is an American automatic test equipment (ATE) designer and manufacturer based in North Reading, Massachusetts. Teradyne's high-profile customers include Samsung, Qualcomm, Intel, Analog Devices, Texas Instruments and IBM. Histo ...

ATE equipment, in a system known as the TSD (Test System Director). As such, they were in use until their software was rendered inoperable by the

Year 2000 problem The year 2000 problem, also known as the Y2K problem, Y2K scare, millennium bug, Y2K bug, Y2K glitch, Y2K error, or simply Y2K refers to potential computer errors related to the formatting and storage of calendar data for dates in and after ...

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

Brookhaven National Laboratory Brookhaven National Laboratory (BNL) is a United States Department of Energy national laboratory located in Upton, Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base and Japanese internment c ...

. In 1976, Samuel C. C. Ting received the

Nobel Prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to humankind." Alfr ...

for this discovery.

Emulators

Ersatz-11

Ersatz-11, a product of D Bit, emulates the PDP-11 instruction set running under DOS, OS/2, Windows, Linux or bare metal (no OS). It can be used to run RSTS or other PDP-11 operating systems.

SimH

SimH is an emulator that compiles and runs on a number of platforms (including

) and supports hardware emulation for the DEC PDP-1, PDP-8, PDP-10, PDP-11, VAX, AltairZ80, several IBM mainframes, and other minicomputers. Hardware kits are available that emulate a PDP-11 front panel, using SimH as the PDP-11 implementation

Notes

Explanatory citations

Citations

References

* *

External links

* BitSaver
PDFsSoftware
directories. * http://archive.computerhistory.org/resources/text/DEC/pdp-11/

Preserving the PDP-11 Series of 16-bit minicomputers
*

Digital PDP11 1969
vintagecomputer.net *
"how to program a PDP-11/10" video

Russian versions of PDP-11 computers

PDP-11/70 CPU core and SoC
''a complete PDP-11 system: a 11/70 CPU with memory management unit, but without floating point unit, a basic set of UNIBUS peripherals (DL11, LP11, PC11, RK11/RK05), a cache and memory controllers for SRAM and PSRAM'' on FPGA *
Ersatz-11, a PDP-11 emulator for DOS, OS/2, Windows and Linux

PDP-11, VAX, Alpha Software archive

PiDP-11, a modern-day PDP-11/70 replica
* {{Authority control PDP-11, Computer-related introductions in 1970 16-bit computers