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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 ...
minicomputers 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 (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 system allowed external devices to be easily interfaced to the system using direct memory access, 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 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
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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 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. This was a 12-bit design adapted from the 1962 LINC 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-5 was a success, ultimately selling about 1,000 machines. This led to the PDP-8, 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. The next year they introduced the 16-bit Data General Nova. 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 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 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 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 called the Unibus, 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 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
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, 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. 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 interrupts 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; 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). 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. 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 includes a debugger: 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 ...
or current loop) 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
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, 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 (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 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 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. For a decade, the PDP-11 was the smallest system that could run
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, ...
, 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 microprocessor could outperform the PDP-11/23 when running Unix. Newer microprocessors such as 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 ...
(1979) and Intel 80386 (1985) also included 32-bit logical addressing. The 68000 in particular facilitated the emergence of a market of increasingly powerful scientific and technical
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
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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 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, which was proprietary but offered a degree of Unix compatibility; and the
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IRIS range, which developed into Unix-based workstations by 1985 (IRIS 2000). Personal computers based on the 68000 like the
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and
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or the Commodore Amiga 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 ...
's
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
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 ...
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-11/45 (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-11/35 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 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
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 ...
, 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 large-scale integration ICs, this system uses a four-package MCP-1600 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 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. * 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 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 and 80286 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-11M+ 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 operating system was eventually ported to the PRO series. A port of RSTS/E 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 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. * H11Heathkit 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 – 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. * The
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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, SM-1420, 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, and some models of the SM EVM 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 ...
). * SM-4, SM-1420, 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 ...
). * SM-4, 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 ...
in
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) 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 state-owned companies and 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. * 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 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 ...
.


Operating systems

Several operating systems were available for the PDP-11


From Digital

* Commercial Operating System * DEC BATCH-11/DOS-11, BATCH-11/DOS-11 * CAPS-11 (Cassette Programming System) * CHRONIC Hierarchical Storage Controller executive * GAMMA-11 * MUMPS, DSM-11 * RSX-11, IAS * RSX-11, P/OS * RSTS/E * RSX-11 * RT-11 * TRAX (Transaction Processing system), TRAX (Transaction Processing system) * Ultrix-11


From third parties

* ANDOS * CSI-DOS * DEIMOS (University of Edinburgh) * DEMOS (Soviet Union) * Duress (operating system), Duress (University of Illinois at Urbana–Champaign/
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 ...
) * LOS/C, a small unitasking system written by BRL for the BRL routers and the I/O controller for the Denelcor HEP * Multi-Environment Real-Time, MERT * Micropower Pascal * MK-DOS * MONECS * Multi-Tasking System, MTS (Multi-Tasking System written in RTL/2 by SPL) * MUMPS * MUSS-11 * PC11 (Decus 11-501/Pilkington) * polyForth, Forth Inc.'s Forth (programming language), Forth for the PDP-11 * ROSTTP (Realtime Operating System for Terminal Teletype Processing/Simpact) * SHAREeleven, SHAREplus * Solo by Per Brinch Hansen * Sphere (operating system), Sphere (Infosphere – Portland Oregon 1981–87) * Softech Microsystems UCSD System with UCSD Pascal * TRIPOS * TSX-Plus *
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, ...
(many versions, including Version 6 Unix, Version 7 Unix, UNIX System III, and Berkeley Software Distribution#PDP-11 beginnings, 2BSD) * Xinu OS for instructional purposes * Venix (implementation/port of Unix developed by VenturCom)


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, Systems Network Architecture, SNA gateways, router (computing), routers, and terminal servers. Ethernet adaptors, such as the DEQNA Q-Bus card, were also available. Many of the earliest systems on the ARPANET were PDP-11's


Peripherals

A wide range of peripherals were available; some of them were also used in other DEC systems like the PDP-8 or
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 ...
. The following are some of the more common PDP-11 peripherals. * CR11 – punched card reader * DL11 – single serial line for either
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 ...
or current loop * LA30/LA36 – DECwriter Dot matrix printer, dot-matrix printing keyboard terminal * LP11 – high speed line printer * PC11 – high speed papertape reader/punch * RA, RD series – fixed platter hard disk * RK05, RK series – hard disk with exchangeable platter * RL02, RL01/RL02 – hard disk with exchangeable platter * RM, RP series – exchangeable multi-platter hard disk * RX01/RX02 – 8-inch floppy disk * RX50/RX33 – 5.25 floppy disk * TU10 – 9 track tape drive * TU56 – DECtape Block (data storage), block-addressed tape system * VT05/VT50/VT52/ VT100 – 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, scientific, educational, medical, or business computing. Another common application was Real-time computing, real-time process control and factory automation. 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. An example of such use of PDP-11s was the management of the packet switched network Datanet 1. 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. The software for the Therac-25 medical linear particle accelerator 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 Automatic test equipment, 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 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. In 1976, Samuel C. C. Ting received the Nobel Prize 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
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 ...
) 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


See also

* Heathkit H11, a 1977 Heathkit personal computer based on the PDP-11 * MACRO-11, the PDP-11's native assembly language * PL-11, a high-level assembler for the PDP-11 written at CERN


Notes


Explanatory citations


Citations


References

* *


Further reading

* *


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