PDP-11
Encyclopedia
The PDP-11 was a series of 16-bit
minicomputer
s sold by Digital Equipment Corporation
(DEC) from 1970 into the 1990s, one of a succession of products in the PDP
series. The PDP-11 replaced the PDP-8 in many real-time applications
, although both product lines lived in parallel for more than 10 years. The PDP-11 had several uniquely innovative features, and was easier to program than its predecessors with its use of general registers. Its successor in the mid-range minicomputer niche was the 32-bit
VAX-11
.
Design features of the PDP-11 influenced the design of microprocessors such as the Motorola
68000
; design features of its operating systems, as well as other operating systems from Digital Equipment, influenced the design of other operating systems such as CP/M
and hence also MS-DOS
. The first officially named version of Unix
ran on the PDP-11/20 in 1970. It is commonly stated that the C programming language
took advantage of several low-level PDP-11–dependent programming features, albeit not originally by design.
, which had a 16-bit word length; DEC's previous PDP-8
had only 12 bit words. 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. Initially manufactured of small-scale Transistor-transistor logic
, a single-board large scale integration version of the processor was developed in 1975. A single-chip processor, the J-11 was developed in 1979. The last models of the PDP-11 line were the PDP-11/94 and -11/93 introduced in 1990.
. For example, instead of instructions such as load and store, the PDP-11 had a move instruction for which either operand (source and destination) could be memory or register. There were no specific input or output instructions; the PDP-11 used memory-mapped I/O
and so the same move instruction was used; orthogonality would even let you move data directly from an input device to an output device. More complex instructions such as add likewise could have memory, register, input, or output as source or destination.
Generally, any operand could apply any of eight addressing modes to eight registers. The addressing modes provided register, immediate, absolute, relative, deferred (indirect), and indexed addressing, and could specify autoincrementation and autodecrementation of a register by one (byte instructions) or two (word instructions). Use of relative addressing let a machine-language program be position-independent
.
For these reasons, PDP-11 programmers viewed the assembly language as easy to learn and uniquely elegant.
for input/output
; it had only a memory bus called the Unibus
. All input and output devices were mapped to memory addresses, so no special I/O instructions were needed.
An input/output device determined the memory addresses to which it would respond, the interrupt priority it would request, and specified its own interrupt vector
. 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.
This Unibus was one reason why the PDP-11 became so appreciated for specific usages. One of the predecessors of Alcatel-Lucent
, the Bell Telephone Manufacturing Company, developed the BTMC DPS-1500 packet-switching (X.25
) network and used PDP-11s in the regional and national network management system, with the Unibus directly connected to the DPS-1500 hardware.
Higher-performance members of the PDP-11 family, starting with the PDP-11/45 Unibus and 11/83 Q-bus systems, departed from the single bus approach. Instead, memory was interfaced by dedicated circuitry and space in the CPU
cabinet, while the Unibus continued to be used for I/O only. 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, a small amount of additional programming was necessary to set up the added bus interfaces.
). The event that caused the interrupt was indicated by the device itself, as it informed the processor of the address of its own interrupt vector.
Interrupt vectors were 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 contained 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.
backplane
. That is, the printed circuit board
s plugged into a backplane connector. The backplane connectors had square pins that could be connected to by wrapping wires around them. The corners of the pins would bite into the wire to form a gas-tight (i.e. corrosion-proof, therefore reliable) connection.
The LSI-11 (PDP-11/03), introduced in February, 1975 was the first PDP-11 model produced using large-scale integration; the entire CPU was contained on four LSI chips made by Western Digital
(the MCP-1600
chip set; a fifth chip could be added to extend the instruction set, as pictured on the right). It used a bus which was a close variant of the Unibus called the LSI Bus or Q-Bus
; it differed from the Unibus primarily in that addresses and data were multiplexed onto a shared set of wires, as opposed to having separate sets of wires, as in the Unibus. It also differed slightly in how it addressed I/O devices and it eventually allowed a 22-bit physical address (whereas the Unibus only allowed an 18-bit physical address) and block-mode operations for significantly improved bandwidth (which the Unibus did not support).
The CPU's microcode
includes a debugger
: firmware with a direct serial interface (RS-232
or current loop
) to a terminal
. This let the operator do debugging
by typing commands and reading octal
numbers, rather than operating switches and reading lights, the typical debugging method at the time. The operator could 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 disabled the microcode itself). The operator could also specify which disk to boot
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 were 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 peripherals, 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).
of the Unibus and Q-bus started to become a system-performance bottleneck
, 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 VAXes provided a PDP-11 compatibility mode under which much existing software could be immediately used, in parallel with newer 32-bit software.
In the 1980s, the IBM PC and its clones largely took over the small computer market, and DEC was unable to counter this competition.
Newer microprocessor
chips such as the Motorola 68000
(1979) and Intel 80386
(1985) also included 32-bit logical addressing. 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.
DEC discontinued PDP-11 production in 1997, and in 1994 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. For several years, Mentec produced new PDP-11 processors. Other companies found a niche market
for replacements for legacy PDP-11 processors, disk subsystems, etc.
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.
and one intended for end-users. Although all models shared 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.
The following models used the Unibus as their principal bus:
The following models used the Q-Bus as their principal bus:
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 was an option which combined two of the microms into one dual carrier, freeing one socket for an EIS/FIS chip. The /150 in combination with a VT-105 terminal was also sold as MiniMINC, a budget version of the MINC-11.
The DEC Professional
series were desktop PCs intended to compete with IBM's earlier 8088 and 80286 based personal computers. The models were equipped with 5¼ inch floppy disk drives and hard disks, except the 325 which had 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, their ill fate in the market was no surprise for anyone except DEC. The RT-11
was eventually ported to the PRO series. A port to the PRO for RSTS/E
was also done internal to DEC, but was not released. The PRO-325 and -350 units were based on the DCF-11 ("Fonz") chipset, the same as found in the 11/23, 11/23+ and 11/24. The PRO-380 was 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.
However conspiracy or not, DEC was never able to successfully migrate its entire PDP-11 customer base to the VAX. The primary reason was not performance, but the PDP-11's superior real-time responsiveness.
countries. At least some of these were pin-compatible with DEC's PDP-11s and could share peripherals and system software. These include:
or PDP-10
.
The following are some of the more common PDP-11 peripherals.
process control
and factory automation.
Some OEM
models also were frequently used as embedded systems to control complex systems like traffic-light systems, medical systems, numerical control
led 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 accelerator also ran on a 32K PDP 11/23.
Another use was for storage of test programs for Teradyne
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
.
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
minicomputer
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
s sold by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
(DEC) from 1970 into the 1990s, one of a succession of products in the PDP
Programmed Data Processor
Programmed Data Processor was the name of a series of minicomputers made by Digital Equipment Corporation. The name 'PDP' intentionally avoided the use of the term 'computer' because, at the time of the first PDPs, computers had a reputation of being large, complicated, and expensive machines, and...
series. The PDP-11 replaced the PDP-8 in many real-time applications
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
, although both product lines lived in parallel for more than 10 years. The PDP-11 had several uniquely innovative features, and was easier to program than its predecessors with its use of general registers. Its successor in the mid-range minicomputer niche was the 32-bit
32-bit
The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory....
VAX-11
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
.
Design features of the PDP-11 influenced the design of microprocessors such as the Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...
; design features of its operating systems, as well as other operating systems from Digital Equipment, influenced the design of other operating systems such as CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
and hence also MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
. The first officially named version of Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
ran on the PDP-11/20 in 1970. It is commonly stated that the C programming language
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
took advantage of several low-level PDP-11–dependent programming features, albeit not originally by design.
History
DEC developed the 16-bit PDP 11 as a response to the introduction of the Data General NOVAData General Nova
The Data General Nova was a popular 16-bit minicomputer built by the American company Data General starting in 1969. The Nova was packaged into a single rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world, and...
, which had a 16-bit word length; DEC's previous PDP-8
PDP-8
The 12-bit PDP-8 was the first successful commercial minicomputer, produced by Digital Equipment Corporation in the 1960s. DEC introduced it on 22 March 1965, and sold more than 50,000 systems, the most of any computer up to that date. It was the first widely sold computer in the DEC PDP series of...
had only 12 bit words. 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. Initially manufactured of small-scale Transistor-transistor logic
Transistor-transistor logic
Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...
, a single-board large scale integration version of the processor was developed in 1975. A single-chip processor, the J-11 was developed in 1979. The last models of the PDP-11 line were the PDP-11/94 and -11/93 introduced in 1990.
Instruction set orthogonality
The PDP-11 processor architecture had a mostly orthogonal instruction setOrthogonal instruction set
Orthogonal instruction set is a term used in computer engineering. A computer's instruction set is said to be orthogonal if any instruction can use data of any type via any addressing mode...
. For example, instead of instructions such as load and store, the PDP-11 had a move instruction for which either operand (source and destination) could be memory or register. There were no specific input or output instructions; the PDP-11 used memory-mapped I/O
Memory-mapped I/O
Memory-mapped I/O and port I/O are two complementary methods of performing input/output between the CPU and peripheral devices in a computer...
and so the same move instruction was used; orthogonality would even let you move data directly from an input device to an output device. More complex instructions such as add likewise could have memory, register, input, or output as source or destination.
Generally, any operand could apply any of eight addressing modes to eight registers. The addressing modes provided register, immediate, absolute, relative, deferred (indirect), and indexed addressing, and could specify autoincrementation and autodecrementation of a register by one (byte instructions) or two (word instructions). Use of relative addressing let a machine-language program be position-independent
Position-independent code
In computing, position-independent code or position-independent executable is machine instruction code that executes properly regardless of where in memory it resides...
.
For these reasons, PDP-11 programmers viewed the assembly language as easy to learn and uniquely elegant.
No dedicated I/O instructions
In the most radical departure from earlier computers, the initial models of the PDP-11 had no dedicated busComputer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
for input/output
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
; it had only a memory bus called the Unibus
Unibus
The Unibus was the earliest of several computer bus technologies used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.-History:...
. All input and output devices were mapped to memory addresses, so no special I/O instructions were needed.
An input/output device determined the memory addresses to which it would respond, the interrupt priority it would request, and specified its own interrupt vector
Interrupt vector
An interrupt vector is the memory address of an interrupt handler, or an index into an array called an interrupt vector table that contains the memory addresses of interrupt handlers...
. 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.
This Unibus was one reason why the PDP-11 became so appreciated for specific usages. One of the predecessors of Alcatel-Lucent
Alcatel-Lucent
Alcatel-Lucent is a global telecommunications corporation, headquartered in the 7th arrondissement of Paris, France. It provides telecommunications solutions to service providers, enterprises, and governments around the world, enabling these customers to deliver voice, data, and video services...
, the Bell Telephone Manufacturing Company, developed the BTMC DPS-1500 packet-switching (X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
) 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, starting with the PDP-11/45 Unibus and 11/83 Q-bus systems, departed from the single bus approach. Instead, memory was interfaced by dedicated circuitry and space in the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
cabinet, while the Unibus continued to be used for I/O only. 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
Massbus
The Massbus was a high-performance computer input/output bus designed in the 1970s by the Digital Equipment Corporation of Maynard, Massachusetts....
. Although input/output devices continued to be mapped into memory addresses, a small amount of additional programming was necessary to set up the added bus interfaces.
Interrupts
The PDP-11 supported hardware interrupts at four priority levels. Interrupts were serviced by software service routines, which could specify whether they themselves could be interrupted (achieving interrupt nestingNesting (computing)
In computing science and informatics, the word nesting may denote several different constructions and activities where information is organized in layers or objects contain other similar objects. The rather general term is thus used in quite specific ways for various situations and concepts...
). The event that caused the interrupt was indicated by the device itself, as it informed the processor of the address of its own interrupt vector.
Interrupt vectors were 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 contained 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
Finally, the PDP-11 was designed to be produced in a factory by semiskilled labor. All of the dimensions of its pieces were relatively non-critical. It used a wire-wrappedWire wrap
Wire wrap is a technology used to assemble electronics. It is a method to construct circuit boards without having to make a printed circuit board. Wires can be wrapped by hand or by machine, and can be hand-modified afterwards. It was popular for large-scale manufacturing in the 60s and early 70s,...
backplane
Backplane
A backplane is a group of connectors connected 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 backbone to connect several printed circuit boards together to make up a complete...
. That is, the printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s plugged into a backplane connector. The backplane connectors had square pins that could be connected to by wrapping wires around them. The corners of the pins would bite into the wire to form a gas-tight (i.e. corrosion-proof, therefore reliable) connection.
LSI-11
Western Digital
Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...
(the MCP-1600
MCP-1600
The MCP-1600 was a multi-chip microprocessor made by Western Digital in the late 1970s through the early 1980s. Used in the Pascal MicroEngine, the original AlphaMicro system, and the DEC LSI-11 microcomputer, a cost-reduced and compact implementation of the DEC PDP-11.There were three types of...
chip set; a fifth chip could be added to extend the instruction set, as pictured on the right). It used a bus which was a close variant of the Unibus called the LSI Bus or Q-Bus
Q-Bus
The Q-bus was one of several bus technologies used with PDP and MicroVAX computer systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts....
; it differed from the Unibus primarily in that addresses and data were multiplexed onto a shared set of wires, as opposed to having separate sets of wires, as in the Unibus. It also differed slightly in how it addressed I/O devices and it eventually allowed a 22-bit physical address (whereas the Unibus only allowed an 18-bit physical address) and block-mode operations for significantly improved bandwidth (which the Unibus did not support).
The CPU's microcode
Microcode
Microcode is a layer of hardware-level instructions and/or data structures involved in the implementation of higher level machine code instructions in many computers and other processors; it resides in special high-speed memory and translates machine instructions into sequences of detailed...
includes a debugger
Debugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
: firmware with a direct serial interface (RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
or current loop
Current loop
A current loop describes two different electrical signalling schemes.- Digital :For digital serial communications, a current loop is a communication interface that uses current instead of voltage for signaling...
) to a terminal
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
. This let the operator do debugging
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
by typing commands and reading octal
Octal
The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. Numerals can be made from binary numerals by grouping consecutive binary digits into groups of three...
numbers, rather than operating switches and reading lights, the typical debugging method at the time. The operator could 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 disabled the microcode itself). The operator could also specify which disk to boot
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
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 were 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 peripherals, 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
Power-on self-test
Power-On Self-Test refers to routines run immediately after power is applied, by nearly all electronic devices. Perhaps the most widely-known usage pertains to computing devices...
(POST).
Decline
The basic design of the PDP-11 was flexible, and was continually updated to use newer technologies. However, the limited throughputThroughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...
of the Unibus and Q-bus started to become a system-performance bottleneck
Bottleneck
A bottleneck is a phenomenon where the performance or capacity of an entire system is limited by a single or limited number of components or resources. The term bottleneck is taken from the 'assets are water' metaphor. As water is poured out of a bottle, the rate of outflow is limited by the width...
, 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
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
(for "Virtual Address eXtension") overcame the 16-bit limitation, but was initially a superminicomputer aimed at the high-end time-sharing
Time-sharing
Time-sharing is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major technological shift in the history of computing.By allowing a large...
market. The early VAXes provided a PDP-11 compatibility mode under which much existing software could be immediately used, in parallel with newer 32-bit software.
In the 1980s, the IBM PC and its clones largely took over the small computer market, and DEC was unable to counter this competition.
Newer microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
chips such as the Motorola 68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...
(1979) and Intel 80386
Intel 80386
The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...
(1985) also included 32-bit logical addressing. 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
DEC Professional (computer)
The Professional 325 and Professional 350 were PDP-11 compatible microcomputers introduced in 1982 by Digital Equipment Corporation as high-end competitors to the IBM PC...
series, failed commercially, along with other non-PDP-11 PC offerings from DEC.
DEC discontinued PDP-11 production in 1997, and in 1994 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. For several years, Mentec produced new PDP-11 processors. Other companies found a niche market
Niche market
A niche market is the subset of the market on which a specific product is focusing; therefore the market niche defines the specific product features aimed at satisfying specific market needs, as well as the price range, production quality and the demographics that is intended to impact...
for replacements for legacy PDP-11 processors, disk subsystems, etc.
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 tended to fall into several natural groups depending on the original design upon which they are based and which I/O bus they used. Within each group, most models were offered in two versions, one intended for OEMsOriginal Equipment Manufacturer
An original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...
and one intended for end-users. Although all models shared 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
- PDP-11/20 and PDP-11/15 — The original, non-microprogrammed processor; designed by Jim O'Loughlin. Floating pointFloating pointIn computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
was supported by peripheralPeripheralA peripheral is a device attached to a host computer, but not part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture....
options using various data formats. - PDP-11/35 and PDP-11/40 — A microprogrammed successor to the PDP-11/20; the design team was led by Jim O'Loughlin.
- PDP-11/45, PDP-11/50, and PDP-11/55 — A much faster microprogrammed processor that could use up to 256 kBKilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
of semiconductor memory instead of or in addition to core memory. First model to support an optional FP11 floating-point coprocessorCoprocessorA coprocessor is a computer processor used to supplement the functions of the primary processor . Operations performed by the coprocessor may be floating point arithmetic, graphics, signal processing, string processing, or encryption. By offloading processor-intensive tasks from the main processor,...
, which established the format used in later models. - PDP-11/70 — The 11/45 architecture expanded to allow 4 MBMegabyteThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
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-11/05 and PDP-11/10 — A cost-reduced successor to the PDP-11/20.
- PDP-11/34 and PDP-11/04 — 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 supported up to 256 kB of Unibus memory. The PDP-11/34a supported a fast floating-point option, and the 11/34c supported a cache memory option.
- PDP-11/60 — A PDP-11 with user-writable microcontrol store; this was designed by another team led by Jim O'Loughlin.
- PDP-11/44 — Replacement for the 11/45 and 11/70 that supported optional cache memory and floating-point processor, and included 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 gateLogic gateA logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
s; later models were all microprogrammed. - PDP-11/24 — First VLSI PDP-11 for Unibus, using the "Fonz-11" (F11) chip set with a Unibus adapter.
- PDP-11/84 — Using the VLSI "Jaws-11"DEC J-11The J-11 is a microprocessor chip set that implements the PDP-11 instruction set architecture jointly developed by Digital Equipment Corporation and Harris Semiconductor. It was a high-end chip set designed to integrate the performance and features of the PDP-11/70 onto a handful of chips...
(J11) chip set with a Unibus adapter. - PDP-11/94 — J11-based, faster than 11/84.
Q-bus models
- PDP-11/03 (also known as the LSI-11/03) — The first LSI PDP-11, this system used a chipset from Western Digital and supported 60 kB of memory.
- PDP-11/23 — 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.
- MicroPDP-11/73PDP-11/73The PDP-11/73 was the third generation of the PDP-11 series of 16-bit minicomputers produced by Digital Equipment Corporation to use LSI processors...
— The third generation LSI-11, this system used the faster "Jaws-11" (J-11DEC J-11The J-11 is a microprocessor chip set that implements the PDP-11 instruction set architecture jointly developed by Digital Equipment Corporation and Harris Semiconductor. It was a high-end chip set designed to integrate the performance and features of the PDP-11/70 onto a handful of chips...
) chip set and supported 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 - QBUS card (M7616) with PDP-11 based peripheral processor and DMA controller. Based on a J11 CPU equipped with 512 kB of RAM, 64 kB of ROM, and parallel and serial interfaces.
- Mentec M100Mentec PDP-11Mentec Limited was founded in 1978 and initially focused on the development of monitoring and control software and systems. It was a significant Digital reseller and OEM in Ireland....
— 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 M11Mentec PDP-11Mentec Limited was founded in 1978 and initially focused on the development of monitoring and control software and systems. It was a significant Digital reseller and OEM in Ireland....
— Processor upgrade board; microcode implementation of PDP-11 instruction set by Mentec, using the TI 8832 ALU and TI 8818 microsequencer from Texas InstrumentsTexas InstrumentsTexas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
. - Mentec M1 — Processor upgrade board; microcode implementation of PDP-11 instruction set by Mentec, using AtmelAtmelAtmel Corporation is a manufacturer of semiconductors, founded in 1984. Its focus is on system-level solutions built around flash microcontrollers...
0.35 μmMicrometreA micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
ASICASICASIC may refer to:* Application-specific integrated circuit, an integrated circuit developed for a particular use, as opposed to a customised general-purpose device.* ASIC programming language, a dialect of BASIC...
. - 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
VT100
The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...
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 was an option which combined two of the microms into one dual carrier, freeing one socket for an EIS/FIS chip. The /150 in combination with a VT-105 terminal was also sold as MiniMINC, a budget version of the MINC-11.
- PRO-325
- PRO-350
- PRO-380
The DEC Professional
DEC Professional (computer)
The Professional 325 and Professional 350 were PDP-11 compatible microcomputers introduced in 1982 by Digital Equipment Corporation as high-end competitors to the IBM PC...
series were desktop PCs intended to compete with IBM's earlier 8088 and 80286 based personal computers. The models were equipped with 5¼ inch floppy disk drives and hard disks, except the 325 which had no hard disk. The original operating system was P/OS, which was essentially RSX-11M+
RSX-11
RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
with a menu system on top. As the design was intended to avoid software exchange with existing PDP-11 models, their ill fate in the market was no surprise for anyone except DEC. The RT-11
RT-11
RT-11 was a small, single-user real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit computers...
was eventually ported to the PRO series. A port to the PRO for RSTS/E
RSTS/E
RSTS is a multi-user time-sharing operating system, developed by Digital Equipment Corporation , for the PDP-11 series of 16-bit minicomputers. The first version of RSTS was implemented in 1970 by DEC software engineers that developed the TSS-8 time-sharing operating system for the PDP-8...
was also done internal to DEC, but was not released. The PRO-325 and -350 units were based on the DCF-11 ("Fonz") chipset, the same as found in the 11/23, 11/23+ and 11/24. The PRO-380 was 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 BusVAXBI BusThe VAXBI bus was a computer bus designed and sold by the Digital Equipment Corporation of Maynard, Massachusetts....
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 11/74's (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 uniprocessorUniprocessorA uniprocessor system is a computer system with a single central processing unit. As more and more computers employ multiprocessing architectures, such as SMP and MPP, the term is used to refer to systems that still have only one CPU. Most desktop computers are now shipped with multiprocessing...
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. Rumor held that the reason the 11/74 was cancelled was due to its higher performance compared to the 11/780 (see, for example http://www.classiccmp.org/pipermail/cctech/2006-February/057197.html). Marketing was therefore concerned that the availability of a higher performing PDP-11 would slow migration to the new VAX. Rather, the ability to maintain the product in the field was the issue.
However conspiracy or not, DEC was never able to successfully migrate its entire 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
- GT40DEC GT40DEC GT40 is an VT11 vector graphic terminal produced by the Digital Equipment Corporation, first introduced in October, 1972 .The DEC GT40 consists of:* CPU: KD11-B...
— VT11 vector graphicsVector graphicsVector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...
terminal using a PDP-11/05. - 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.
- H-11Heathkit H-11The Heathkit H11 Computer was an early kit-format personal computer introduced in 1977. It was essentially a Digital Equipment PDP-11 in a small form factor case, designed by Heathkit...
— HeathkitHeathkitHeathkits were products of the Heath Company, Benton Harbor, Michigan. Their products included electronic test equipment, high fidelity home audio equipment, television receivers, amateur radio equipment, electronic ignition conversion modules for early model cars with point style ignitions, and...
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 QBUS backplane with direct mapped character display for text editing and typesetting.
- VT103 — VT100 with backplane to host an LSI-11.
- VT173 — A high-end typseset terminal containing an 11/03. One use for it was as a terminal with DECset, a typesetting/publishing software running on VMS 3.x (later, DEC reused the name DECset). The terminal software was loaded at boot time from the VMS system. DECset was the DEC OEM version of the Datalogics PAGER application running on PDP-11 or VAX in compatibility mode.
- 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.mmpC.mmpThe C.mmp was an early MIMD multiprocessor system developed at Carnegie Mellon University by William Wulf . The notation C.mmp came from the PMS notation of Bell and Newell, where a CPU was designated as C and a variant was noted by the dot notation; mmp stood for Multi-Mini-ProcessorSixteen...
— Multiprocessor system from Carnegie Mellon UniversityCarnegie Mellon UniversityCarnegie Mellon University is a private research university in Pittsburgh, Pennsylvania, United States....
. - SBC 11/21 (boardname KXT11) Falcon and Falcon Plus — single board computer on a Qbus card implementing the basic PDP-11 instruction set, based on T11 chipset containing 32 KB static RAM, two ROM sockets, three serial lines, 20 bit parallel I/O, three interval timers and a two-channel DMA controller. Up to 14 Falcons could be placed into one Qbus system.
- KXJ11 — QBUS card (M7616) with PDP-11 based peripheral processor and DMA controller. Based on a J11 CPU equipped with 512 kB RAM, 64 kB ROM and parallel and serial interfaces.
- HSC high end CI disk controllers used backplane mounted J11 and F11 processor cards to run their CHRONIC operating system.
Unauthorized clones
The PDP-11 was sufficiently popular that many unauthorized PDP-11-compatible minicomputers and microcomputers were produced in Eastern BlocEastern bloc
The term Eastern Bloc or Communist Bloc refers to the former communist states of Eastern and Central Europe, generally the Soviet Union and the countries of the Warsaw Pact...
countries. At least some of these were pin-compatible with DEC's PDP-11s and could share peripherals and system software. These include:
- SM-4SM-4The SM-4 was a Polish PDP-11/40 computer clone, in the second half of 1980s. It was very popular in science and technology.The standard configuration included 128 or 256 KB core memory, tape puncher, two RK-05 removable 2.5 MB disks and two RK-05F fixed disks, two TU-10 drives and Videoton...
, SM-1420SM-1420The SM-1420 was a PDP-11/34+ clone, and the successor to SM-4 in Soviet Bloc countries. It was produced in the Soviet Union and Bulgaria....
, SM-1600, Elektronika BKElektronika BKThe Elektronika BK was a series of 16-bit PDP-11-compatible Soviet home computers developed by NPO Scientific Center, the leading Soviet microcomputer design team at the time. It was also responsible for the more powerful UKNC and DVK micros...
series, Elektronika 60, Elektronika 85, DVKDVKDVK is a Soviet PDP-11-compatible personal computer.The design is also known as Elektronika MS-0501 and Elektronika MS-0502.Earlier models of DVK series were based on K1801VM1 or K1801VM2 microprocessors with 16 bit address bus. In the later models, the KM1801VM3 microprocessor was used.-...
and UKNCUKNCUKNC was a Soviet PDP-11-compatible educational computer, aimed at teaching school informatics courses. It is also known as Elektronika MS-0511...
(in the Soviet UnionSoviet UnionThe Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
). - SM-4SM-4The SM-4 was a Polish PDP-11/40 computer clone, in the second half of 1980s. It was very popular in science and technology.The standard configuration included 128 or 256 KB core memory, tape puncher, two RK-05 removable 2.5 MB disks and two RK-05F fixed disks, two TU-10 drives and Videoton...
, SM-1420SM-1420The SM-1420 was a PDP-11/34+ clone, and the successor to SM-4 in Soviet Bloc countries. It was produced in the Soviet Union and Bulgaria....
, IZOT-1016 and peripherals (in BulgariaBulgariaBulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...
). - MERA-60 in PolandPolandPoland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
. - SM-1620, SM-1630 (in East Germany).
- SM-4SM-4The SM-4 was a Polish PDP-11/40 computer clone, in the second half of 1980s. It was very popular in science and technology.The standard configuration included 128 or 256 KB core memory, tape puncher, two RK-05 removable 2.5 MB disks and two RK-05F fixed disks, two TU-10 drives and Videoton...
, TPA-1140, TPA-1148, TPA-11/440 (in HungaryHungaryHungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
). - Independent and Coral (in RomaniaRomaniaRomania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...
). - CalData — Made in U.S., ran all DEC OS's
From Digital
- BATCH-11/DOS-11DEC BATCH-11/DOS-11BATCH-11/DOS-11, also known simply as DOS-11, was an operating system by Digital Equipment Corporation of Maynard, Massachusetts. The first version of DOS-11 was released in 1970 and was the first operating system to run on the Digital PDP-11 minicomputer.DOS-11 was not known to be easy to use...
- CAPS-11 (Cassette Based Programme development System)
- GAMMA-11
- DSM-11MUMPSMUMPS , or alternatively M, is a programming language created in the late 1960s, originally for use in the healthcare industry. It was designed for the production of multi-user database-driven applications...
- IASRSX-11RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
- P/OSRSX-11RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
- RSTS/ERSTS/ERSTS is a multi-user time-sharing operating system, developed by Digital Equipment Corporation , for the PDP-11 series of 16-bit minicomputers. The first version of RSTS was implemented in 1970 by DEC software engineers that developed the TSS-8 time-sharing operating system for the PDP-8...
- RSX-11RSX-11RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
- RT-11RT-11RT-11 was a small, single-user real-time operating system for the Digital Equipment Corporation PDP-11 family of 16-bit computers...
- UltrixUltrixUltrix was the brand name of Digital Equipment Corporation's native Unix systems. While ultrix is the Latin word for avenger, the name was chosen solely for its sound.-History:...
-11 - CHRONIC Hierarchical Storage Controller executive
From third parties
- ANDOSANDOSANDOS is a Russian operating system for Electronika BK-0010, Electronika BK-0011 and Electronika BK-0011M series computers. It was created in 1990 and first released in 1992. Initially it was developed by Alexey Nadezhin and later also by Sergey Kamnev, who joined the project...
- CSI-DOSCSI-DOSCSI-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 graphics video mode. The system supported both hard and...
- DEMOSDEMOSDEMOS was a Unix-like operating system developed in the Soviet Union...
(Soviet Union) - Duress (University of Illinois at Urbana-ChampaignUniversity of Illinois at Urbana-ChampaignThe University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
/Datalogics) - FuzzballFuzzball routerFuzzball routers were the first modern routers on the Internet. They were DEC LSI-11 computers loaded with the Fuzzball software written by David L. Mills . The name "Fuzzball" was the colloquialism for Mills' routing software. Six provided the routing backbone of the first 56 kbit/s NSFnet,...
- MERT
- Micropower Pascal
- MK-DOSMK-DOSMK-DOS was one of the most widespread operating systems for Elektronika BK Soviet personal computers, developed by Mikhail Korolev and Dmitriy Butyrskiy from 1993. Like ANDOS, the system provided full compatibility of operating environments for all models of BK, emulating environments of the...
- MONECSMONECSMONECS was a computer operating system with BASIC, COBOL, FORTRAN, Pascal compilers, plus machine language facility...
- MTS (Multi-Tasking System written in RTL/2RTL/2RTL/2 was a high-level programming language developed at Imperial Chemical Industries Ltd by J.G.P. Barnes. It was originally used internally within ICI but was distributed by SPL International in 1974...
by SPL) - MUMPSMUMPSMUMPS , or alternatively M, is a programming language created in the late 1960s, originally for use in the healthcare industry. It was designed for the production of multi-user database-driven applications...
- PC11 (Decus 11-501/PilkingtonPilkingtonPilkington Group Limited is a multinational glass manufacturing company headquartered in St Helens, United Kingdom. It is a subsidiary of the Japan-based NSG Group...
) - polyForth, Forth Inc.'s ForthForthForth is a structured, imperative, reflective, concatenative, extensible, stack-based computer programming language and programming environment...
for the PDP-11 - ROSTTP (Realtime Operating System for Terminal Teletype Processing/Simpact)
- Solo by Per Brinch HansenPer Brinch HansenPer Brinch Hansen was a Danish-American computer scientist known for concurrent programming theory.-Biography:He was born in Frederiksberg, in Copenhagen, Denmark....
- Sphere (Infosphere - Portland Oregon 1981-87)
- Softech Microsystems UCSD System with UCSD PascalUCSD PascalUCSD Pascal was a Pascal programming language system that ran on the UCSD p-System, a portable, highly machine-independent operating system. UCSD Pascal was first released in 1978...
- TRAX (Transaction Processing system)
- TRIPOSTRIPOSTRIPOS is a computer operating system. Development started in 1976 at the Computer Laboratory of Cambridge University and it was headed by Dr. Martin Richards. The first version appeared in January 1978 and it originally ran on a PDP-11. Later it was ported to the Computer Automation LSI4 and the...
- TSX-PlusTSX-PlusTSX-Plus is a multi-user operating system for the PDP-11/LSI-11 series of computers. It was developed by S&H Computer Systems, Inc. and is based on DEC's RT-11 single-user real-time operating system...
- UnixUnixUnix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
(many versions, including Version 6 UnixVersion 6 UnixSixth 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 minicomputers...
, Version 7 UnixVersion 7 UnixSeventh 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 commercialization of Unix by AT&T in the early 1980s...
, UNIX System IIIUNIX System IIIUNIX System III was a version of the Unix operating system released by AT&T's Unix Support Group . It was first released outside of Bell Labs in 1982. UNIX System III was a mix of various AT&T Unixes: PWB/UNIX 2.0, CB UNIX 3.0, UNIX/TS 3.0.1 and UNIX/32V...
, and 2BSD) - XinuXinuXinu is a Unix-like operating system originally developed by Douglas Comer for instructional purposes at Purdue University in the 1980s. The name is both recursive, and is "Unix" spelled backwards...
OS for instructional purposes - VenixVenixVenix was a version of the Unix operating system developed by VenturCom.Venix 2.0, based on System III, ran on the DEC PRO-350 microcomputer , the DEC Rainbow 100 as well as PCs . It was released in 1984...
(implementation/port of Unix developed by VenturCom)
Peripherals
A wide range of peripherals were available; some of them were also used in other DEC systems like the PDP-8PDP-8
The 12-bit PDP-8 was the first successful commercial minicomputer, produced by Digital Equipment Corporation in the 1960s. DEC introduced it on 22 March 1965, and sold more than 50,000 systems, the most of any computer up to that date. It was the first widely sold computer in the DEC PDP series of...
or PDP-10
PDP-10
The PDP-10 was a mainframe computer family manufactured by Digital Equipment Corporation from the late 1960s on; the name stands for "Programmed Data Processor model 10". The first model was delivered in 1966...
.
The following are some of the more common PDP-11 peripherals.
- CR11 — punched cardPunched cardA punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...
reader - LA30/LA36 — DECwriter dot-matrixDot matrix printerA dot matrix printer or impact matrix printer is a type of computer printer with a print head that runs back and forth, or in an up and down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a typewriter...
printing keyboard terminal - LP11 — high speed line printerLine printerThe line printer is a form of high speed impact printer in which one line of type is printed at a time. They are mostly associated with the early days of computing, but the technology is still in use...
- PC11 — high speed papertape reader/punch
- RA,RD series — fixed platter hard diskHard diskA hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
- 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 diskFloppy diskA floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
- TU11 — 9-track tape drive
- TU56 — DECtapeDECtapeDECtape, originally called "Microtape", was a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX/VMS support for it was implemented but did not become an...
block-addressed tape system - VT05VT05The VT05 was the first free-standing CRT computer terminal from Digital Equipment Corporation. Famous for its extremely futuristic styling, the VT05 presented the user with an upper-case only 5x7 dot-matrix display of 20 rows by 72 columns. The terminal only supported forward scrolling and direct...
/VT50/VT52VT52The VT52 was a CRT-based computer terminal produced by Digital Equipment Corporation introduced in September, 1975 . It provided a screen of 24 rows and 80 columns of text and supported all 95 ASCII characters as well as 32 graphics characters. It supported asynchronous communication at baud rates...
/VT100VT100The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...
— 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, or business computing. Another common application was real-timeReal-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
process control
Process control
Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range...
and factory automation.
Some OEM
OEM
OEM means the original manufacturer of a component for a product, which may be resold by another company.OEM may also refer to:-Computing:* OEM font, or OEM-US, the original character set of the IBM PC, circa 1981...
models also were frequently used as embedded systems to control complex systems like traffic-light systems, medical systems, numerical control
Numerical control
Numerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to controlled manually via handwheels or levers, or mechanically automated via cams alone...
led machining
Machining
Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...
, or for network-management. An example of such use of PDP-11s was the management of the packet switched network Datanet
Datanet
This article is about the U.S. National Science Foundation Office of Cyberinfrastructure . For the ISP, Datanet please visit Datanet .On September 28, 2007, the U.S. National Science Foundation Office of Cyberinfrastructure announced a request for proposals with the name Sustainable Digital Data...
1. In the 1980s, the UK's air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
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
Therac-25
The Therac-25 was a radiation therapy machine produced by Atomic Energy of Canada Limited after the Therac-6 and Therac-20 units ....
medical linear accelerator also ran on a 32K PDP 11/23.
Another use was for storage of test programs for Teradyne
Teradyne
Teradyne , a US company, is a supplier of automatic test equipment . The company's divisions Semiconductor Test and Systems Test Group, are organized by the products they develop and deliver.-History:...
ATE
Automatic test equipment
Automatic or Automated Test Equipment is any apparatus that performs tests on a device, known as the Device Under Test , using automation to quickly perform measurements and evaluate the test results...
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
Year 2000 problem
The Year 2000 problem was a problem for both digital and non-digital documentation and data storage situations which resulted from the practice of abbreviating a four-digit year to two digits.In computer programs, the practice of representing the year with two...
.
See also
- Heathkit H11, a 1977 Heathkit personal computer based on the PDP-11
- MACRO-11MACRO-11MACRO-11 is an assembly language with macro facilities for PDP-11 minicomputers from Digital Equipment Corporation . It is the successor to PAL-11 , an earlier version of the PDP-11 assembly language without macro facilities....
, the PDP-11's native assembly language - PL-11PL-11PL-11 is a high-level machine-oriented programming language for the PDP-11, developed by R.D. Russell of CERN in 1971. Written in Fortran IV, it is similar to PL360 and is cross-compiled on other machines....
, a high-level assembler for the PDP-11 written at CERN - SIMHSIMHSIMH is a highly portable, multi-system emulator which runs on Windows, Linux, Mac OS X, FreeBSD, OpenBSD, NetBSD, OpenVMS, and other operating systems...
, a multiple minicomputer architecture emulator written in portable C
Further reading
- Michael Singer, PDP-11. Assembler Language Programming and Machine Organization, John Wiley & Sons, NY: 1980.
External links
- The PDP-11 FAQ
- Preserving the PDP-11 Series of 16-bit minicomputers
- Gordon BellGordon BellC. Gordon Bell is an American computer engineer and manager. An early employee of Digital Equipment Corporation 1960–1966, Bell designed several of their PDP machines and later became Vice President of Engineering 1972-1983, overseeing the development of the VAX...
and Bill Strecker's 1975 paper, What We Learned From the PDP-11 - Further papers and links on Gordon Bell's site.
- The Fuzzball
- On LSI-11, RT-11, Megabytes of Memory and Modula-2/VRS by Günter Dotzel, ModulaWare.com - An article on Modula-2 compiler/linker synergy to overcome the PDP/LSI-11 address space limitations, published in DEC Professional: the magazine for DEC users, Professional Press, Spring House, PA. U.S.A., January 1986.
- Programming the PDP-11/10. A video from DePauw University demonstrating how to program a PDP-11/10.
- pdp11.co.uk Site focused the preservation and restoration of PDP-11 computers
- electronica-60.ucoz.com Site focussed on the Russian versions of PDP-11 computers
- PDP-11/70 CPU core and SoC, OpenCores page describing 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