The story
Founded by Harlan Anderson and Ken Olsen in 1957.1
Origins (1944–1958)
Ken Olsen and Harlan Anderson were two engineers who had been working at MIT Lincoln Laboratory on the lab's various computer projects. The Lab is best known for their work on what would today be known as "interactivity", and their machines were among the first where operators had direct control over programs running in real-time. These had started in 1944 with the famed Whirlwind, which was originally developed to make a flight simulator for the US Navy, although this was never completed. Instead, this effort evolved into the SAGE system for the US Air Force, which used large screens and light guns to allow operators to interact with radar data stored in the computer.
When the Air Force project wound down, the Lab turned their attention to an effort to build a version of the Whirlwind using transistors in place of vacuum tubes. In order to test their new circuitry, they first built a small 18-bit machine known as TX-0, which first ran in 1956. When the TX-0 successfully proved the basic concepts, attention turned to a much larger system, the 36-bit TX-2 with a then-enormous 64 kWords of core memory. Core was so expensive that parts of TX-0's memory were stripped for the TX-2, and what remained of the TX-0 was then given to MIT on permanent loan.
At MIT, Ken Olsen and Harlan Anderson noticed something odd: students would line up for hours to get a turn to use the stripped-down TX-0, while largely ignoring a faster IBM machine that was also available. The two decided that the draw of interactive computing was so strong that they felt there was a market for a small machine dedicated to this role, essentially a commercialized TX-0. They could sell this to users where the graphical output or real-time operation would be more important than outright performance. Additionally, as the machine would cost much less than the larger systems then available, it would also be able to serve users that needed a lower-cost solution dedicated to a specific task, where a larger 36-bit machine would not be needed.
In 1957, when the pair and Ken's brother Stan sought capital, they found that the American business community was hostile to investing in computer companies. Many smaller computer companies had come and gone in the 1950s, wiped out when new technical developments rendered their platforms obsolete, and even large companies like RCA and General Electric were failing to make a profit in the market. The only serious expression of interest came from Georges Doriot and his American Research and Development Corporation (AR&D). Worried that a new computer company would find it difficult to arrange further financing, Doriot suggested the fledgling company change its business plan to focus less on computers, and even change their name from "Digital Computer Corporation".
The pair returned with an updated business plan that outlined two phases for the company's development. They would start by selling computer modules as stand-alone devices that could be purchased separately and wired together to produce a number of different digital systems for lab use. Then, if these "digital modules" were able to build a self-sustaining business, the company would be free to use them to develop a complete computer in its Phase II. The newly christened "Digital Equipment Corporation" received $70,000 from AR&D for a 70% share of the company, AR&D's SVP Dorothy Rowe joined as a Director and also served as Treasurer, and the company began operations in a Civil War-era textile mill in Maynard, Massachusetts, where plenty of inexpensive manufacturing space was available.
Digital modules (1958)
In early 1958, DEC shipped its first products, the "Digital Laboratory Module" line. The Modules consisted of a number of individual electronic components and germanium transistors mounted to a circuit board, the actual circuits being based on those from the TX-2.
The Laboratory Modules were packaged in an extruded aluminum housing, intended to sit on an engineer's workbench, although a rack-mount bay was sold that held nine laboratory modules. They were then connected together using banana plug patch cords inserted at the front of the modules. Three versions were offered, running at 5 MHz (1957), 500 kHz (1959), or 10 MHz (1960). The Modules proved to be in high demand by other computer companies, who used them to build equipment to test their own systems. Despite the recession of the late 1950s, the company sold $94,000 worth of these modules during 1958 alone (equivalent to $1,049,000 in 2025), turning a profit at the end of its first year.
The original Laboratory Modules were soon supplemented with the "Digital System Module" line, which were identical internally but packaged differently. The Systems Modules were designed with all of the connections at the back of the module using 22-pin Amphenol connectors, and were attached to each other by plugging them into a backplane that could be mounted in a 19-inch rack. The backplanes allowed 25 modules in a single 5-1/4 inch section of rack, and allowed the high densities needed to build a computer.
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The original laboratory and system module lines were offered in 500 kilocycle, 5 megacycle and 10 megacycle versions. In all cases, the supply voltages were -15 and +10 volts, with logic levels of -3 volts (passive pull-down) and 0 volts (active pull-up).
DEC used the System Modules to build their "Memory Test" machine for testing core memory systems, selling about 50 of these pre-packaged units over the next eight years. The PDP-1 and LINC computers were also built using System Modules (see below).
Modules were part of DEC's product line into the 1970s, although they went through several evolutions during this time as technology changed. The same circuits were then packaged as the first "R" (red) series "Flip-Chip" modules. Later, other Flip-Chip module series provided additional speed, much higher logic density, and industrial I/O capabilities. DEC published extensive data about the modules in free catalogs that became very popular.
PDP-1 family (1960)
With the company established and a successful product on the market, DEC turned its attention to the computer market once again as part of its planned "Phase II". In August 1959, Ben Gurley started design of the company's first computer, the PDP-1. In keeping with Doriot's instructions, the name was an initialism for "Programmable Data Processor", leaving off the term "computer". As Gurley put it, "We aren't building computers, we're building 'Programmable Data Processors'." The prototype was first shown publicly at the Joint Computer Conference in Boston in December 1959. The first PDP-1 was delivered to Bolt, Beranek and Newman in November 1960, and formally accepted the next April. The PDP-1 sold in basic form for $120,000 (equivalent to $1,292,873 in 2025). By the time production ended in 1969, 53 PDP-1s had been delivered.
The PDP-1 was supplied standard with 4096 words of core memory, 18-bits per word, and ran at a basic speed of 100,000 operations per second. It was constructed using many System Building Blocks that were packaged into several 19-inch racks. The racks were themselves packaged into a single large mainframe case, with a hexagonal control panel containing switches and lights mounted to lie at table-top height at one end of the mainframe. Above the control panel was the system's standard input/output solution, a punched tape reader and writer. Most systems were purchased with two peripherals, the Type 30 vector graphics display, and a Soroban Engineering modified IBM Model B Electric typewriter that was used as a printer. The Soroban system was notoriously unreliable, and often replaced with a modified Friden Flexowriter, which also contained its own punched tape system. A variety of more-expensive add-ons followed, including magnetic tape systems, punched card readers and punches, and faster punched tape and printer systems.
When DEC introduced the PDP-1, they also mentioned larger machines at 24, 30 and 36 bits, based on the same design. During construction of the prototype PDP-1, some design work was carried out on a 24-bit PDP-2, and the 36-bit PDP-3. Although the PDP-2 never proceeded beyond the initial design, the PDP-3 found some interest and was designed in full. Only one PDP-3 appears to have been built, in 1960, by the CIA's Scientific Engineering Institute (SEI) in Waltham, Massachusetts. According to the limited information available, they used it to process radar cross section data for the Lockheed A-12 reconnaissance aircraft. Gordon Bell remembered that it was being used in Oregon some time later, but could not recall who was using it.
In November 1962, DEC introduced the $65,000 PDP-4. The PDP-4 was similar to the PDP-1 and used a similar instruction set, but used slower memory and different packaging to lower the price. Like the PDP-1, about 54 PDP-4s were eventually sold, most to a customer base similar to the original PDP-1.
In 1964, DEC introduced its new Flip-Chip module design, and used it to re-implement the PDP-4 as the PDP-7. The PDP-7 was introduced in December 1964, and about 120 were eventually produced. An upgrade to the Flip Chip led to the R series, which in turn led to the PDP-7A in 1965. The PDP-7 is most famous as the machine for which the Unix operating system was originally written. Unix ran only on DEC systems until the Interdata 8/32.
A more dramatic upgrade to the PDP-1 series was introduced in August 1966, the PDP-9. The PDP-9 was instruction-compatible with the PDP-4 and −7, but ran about twice as fast as the −7 and was intended to be used in larger deployments. At only $19,900 in 1968, the PDP-9 was a big seller, eventually selling 445 machines, more than all of the earlier models combined.
Even while the PDP-9 was being introduced, its replacement was being designed, and was introduced as 1969's PDP-15, which re-implemented the PDP-9 using integrated circuits in place of modules. Much faster than the PDP-9 even in basic form, the PDP-15 also included a floating-point unit and a separate input/output processor for further performance gains. Over 400 PDP-15's were ordered in the first eight months of production, and production eventually amounted to 790 examples in 12 basic models. However, by this time other machines in DEC's lineup could fill the same niche at even lower prices, and the PDP-15 would be the last of the 18-bit series.
PDP-8 family (1962)
In 1962, Lincoln Laboratory used a selection of System Building Blocks to implement a small 12-bit machine, and attached it to a variety of analog-to-digital (A to D) input/output (I/O) devices that made it easy to interface with various analog lab equipment. The LINC proved to attract intense interest in the scientific community, and has since been referred to as the first real minicomputer, a machine that was small and inexpensive enough to be dedicated to a single task even in a small lab.
Seeing the success of the LINC, in 1963 DEC took the basic logic design but stripped away the extensive A to D systems to produce the PDP-5. The new machine, the first outside the PDP-1 mould, was introduced at WESCON on August 11, 1963. A 1964 ad expressed the main advantage of the PDP-5, "Now you can own the PDP-5 computer for what a core memory alone used to cost: $27,000". 116 PDP-5s were produced until the lines were shut down in early 1967. Like the PDP-1 before it, the PDP-5 inspired a series of newer models based on the same basic design that would go on to be more famous than its parent.
On March 22, 1965, DEC introduced the PDP-8, which replaced the PDP-5's modules with the new R-series modules using Flip Chips. The machine was re-packaged into a small tabletop case, which remains distinctive for its use of smoked plastic over the CPU which allowed one to easily see the logic modules plugged into the wire-wrapped backplane of the CPU. Sold standard with 4 kWords of 12-bit core memory and a Teletype Model 33 ASR for basic input/output, the machine listed for only $18,000. The PDP-8 is referred to as the first real minicomputer because of its sub-$25,000 price. Sales were, unsurprisingly, very strong, and helped by the fact that several competitors had just entered the market with machines aimed directly at the PDP-5's market space, which the PDP-8 trounced. This gave the company two years of unrestricted leadership, and eventually 1450 "straight eight" machines were produced before it was replaced by newer implementations of the same basic design.
DEC hit an even lower price with the PDP-8/S, the S for "serial". As the name implies the /S used a serial arithmetic unit, which was much slower but reduced costs so much that the system sold for under $10,000. DEC then used the new PDP-8 design as the basis for a new LINC, the two-processor LINC-8. The LINC-8 used one PDP-8 CPU and a separate LINC CPU, and included instructions to switch from one to the other. This allowed customers to run their existing LINC programs, or "upgrade" to the PDP-8, all in software. Although not a huge seller, 142 LINC-8s were sold starting at $38,500. Like the original LINC to PDP-5 evolution, the LINC-8 was then modified into the single-processor PDP-12, adding another 1000 machines to the 12-bit family. Newer circuitry designs led to the PDP-8/I and PDP-8/L in 1968. In 1975, one year after an agreement between DEC and Intersil, the Intersil 6100 chip was launched, effectively a PDP-8 on a chip. This was a way to allow PDP-8 software to be run even after the official end-of-life announcement for the DEC PDP-8 product line.
PDP-6 and PDP-10 families (1963 and 1968)
While the PDP-5 introduced a lower-cost line, 1963's PDP-6 was intended to take DEC into the mainframe market with a 36-bit machine. However, the PDP-6 proved to be a "hard sell" with customers, as it offered few obvious advantages over similar machines from the better-established vendors like IBM or Honeywell, in spite of its low cost around $300,000. Only 23 were sold, or 26 depending on the source, and unlike other models the low sales meant the PDP-6 was not improved with successor versions. However, the PDP-6 is historically important as the platform that introduced "Monitor", an early time-sharing operating system that would evolve into the widely used TOPS-10.
When newer Flip Chip packaging allowed the PDP-6 to be re-implemented at a much lower cost, DEC took the opportunity to refine their 36-bit design, introducing the PDP-10 in 1968. The PDP-10 was as much a success as the PDP-6 was a commercial failure; about 700 mainframe PDP-10s were sold before production ended in 1984. The PDP-10 was widely used in university settings, and thus was the basis of many advances in computing and operating system design during the 1970s. DEC later re-branded all of the models in the 36-bit series as the "DECsystem-10", and PDP-10s are generally referred to by the model of their CPU, starting with the "KA10", soon upgraded to the "KI10" (I:Integrated circuit); then to "KL10" (L:Large-scale integration ECL logic); also the "KS10" (S: Small form factor). Unified product line upgrades produced the compatible DECSYSTEM-20, along with a TOPS-20 operating system that included virtual memory support.
The Jupiter Project was supposed to continue the mainframe product line into the future by using gate arrays with an innovative Air Mover Cooling System, coupled with a built-in floating point processing engine called "FBOX". The design was intended for a top tier scientific computing niche, yet the critical performance measurement was based upon COBOL compilation which did not fully utilize the primary design features of Jupiter technology. When the Jupiter Project was cancelled in 1983, some of the engineers adapted aspects of the 36-bit design into a forthcoming 32-bit design, releasing the high-end VAX8600 in 1985.
PDP-11 (1970)
DEC's successful entry into the computer market took place during a fundamental shift in the underlying organization of the machines from word lengths based on 6-bit characters to those based on 8-bit words needed to support ASCII. DEC began studies of such a machine, the PDP-X, but Ken Olsen did not support it as he could not see how it offered anything their existing 12-bit or 18-bit machines didn't. This led the leaders of the PDP-X project to leave DEC and start Data General, whose 16-bit Data General Nova was released in 1969 and was a huge success.
The success of the Nova finally prompted DEC to take the switch seriously, and they began a crash program to introduce a 16-bit machine of their own. The new system was designed primarily by Harold McFarland, Gordon Bell, Roger Cady, and others. The project was able to leap forward in design with the arrival of Harold McFarland, who had been researching 16-bit designs at Carnegie Mellon University. One of his simpler designs became the basis for the new design, although when they first viewed the proposal, management was not impressed and almost cancelled it.
The result was the PDP-11, released in 1970. It differed from earlier designs considerably. In particular, the new design did not include many of the addressing modes that were intended to make programs smaller in memory, a technique that was widely used on other DEC machines and CISC designs in general. This would mean the machine would spend more time accessing memory, which would slow it down. However, the machine also extended the idea of multiple "General Purpose Registers" (GPRs), which gave the programmer flexibility to use these high-speed memory caches as they needed, potentially addressing the performance issues.
A major advance in the PDP-11 design was DEC's Unibus, which supported all peripherals through memory mapping. This allowed a new device to be added easily, generally only requiring plugging a hardware interface board into the backplane and possibly adding a jumper to the wire wrapped backplane, and then installing software that read and wrote to the mapped memory to control it. The relative ease of interfacing spawned a huge market of third party add-ons for the PDP-11, which made the machine even more useful.
The combination of architectural innovations proved superior to competitors and the "11" architecture was soon the industry leader, propelling DEC back to a strong market position. The design was later expanded to allow paged physical memory and memory protection features, useful for multitasking and time-sharing. Some models supported separate instruction and data spaces for an effective virtual address size of 128 KB within a physical address size of up to 4 MB. Smaller PDP-11s, implemented as single-chip CPUs, continued to be produced until 1996, by which time over 600,000 had been sold.
The PDP-11 supported several operating systems, including Bell Labs' new Unix operating system as well as DEC's DOS-11, RSX-11, IAS, RT-11, DSM-11, and RSTS/E. Many early PDP-11 applications were developed using standalone paper-tape utilities. DOS-11 was the PDP-11's first disk operating system, but was soon supplanted by more capable systems. RSX provided a general-purpose multitasking environment and supported a wide variety of programming languages. IAS was a time-sharing version of RSX-11D. Both RSTS and Unix were time-sharing systems available to educational institutions at little or no cost, and these PDP-11 systems were destined to be the "sandbox" for a rising generation of engineers and computer scientists. Large numbers of PDP-11/70s were deployed in telecommunications and industrial control applications. AT&T Corporation became DEC's largest customer.
From Wikipedia’s article on Digital Equipment Corporation, shared under CC BY-SA 4.0.3