Digital Equipment Corporation

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Digital Equipment Corporation was a pioneering company in the American computer industry. They are generally referred to within the computing industry as DEC. (This acronym was once officially used by DEC itself[1], but discarded in favor of "Digital" in order to avoid a trademark dispute with the Dairy Equipment Company of Madison, Wisconsin). They were later acquired by Compaq, which subsequently merged with Hewlett-Packard. As of 2004 their product lines are still produced under the HP name.

Digital Equipment should not be confused with Digital Research; the two were unrelated, separate entities (despite some similarities between the operating systems they produced).



The company was founded in 1957 by Ken Olsen, a Massachusetts engineer who had been working at MIT Lincoln Laboratory on the TX-2 project. The TX-2 was a transistor-based computer using the then-huge amount of 64K 36-bit words of core memory. When that project ran into difficulties, Olsen left to form DEC with Harlan Anderson, a colleague from his MIT days. At the time the market was hostile to computer companies, and investors shied from their plans. Instead they started building small digital "modules" (each effectively a single component from the TX-2 design) that could be combined together to be used in a lab setting. In 1961 the company was making a profit, and started construction of their first computer, the PDP-1 (PDP being an initialism for Programmable Data Processor).

18-bit Computers

Through the 1960s DEC produced a series of machines aimed at a price/performance point below IBM's mainframe machines, typically based on an 18-bit word, using core memory: the PDP-1, the PDP-2, the PDP-4 (1963), PDP-9 (1965), and finally the PDP-15 series (starting in 1970). The PDP-15 was an early user of integrated circuits. These computers were moderately powerful computers for their time, mainly used in industrial and medical laboratories.

12-bit Computers

To serve laboratories at a lower cost, DEC provided the PDP-5, an early minicomputer in 1963. True success followed with the introduction of the famous PDP-8 in 1964. It was a smaller, 12-bit word machine that sold for about $16,000. The PDP-8 was small enough to fit on a cart. It was simple enough to be used for many roles, and they soon started being sold in huge numbers to new market niches, labs, railways, and all sorts of industrial applications.

The PDP-8 was important historically because it was the first computer that was regularly purchased by a handful of end users as an alternative to using a larger system in a data center. Because of their low cost and portability, these machines could be purchased to fill a specific need, unlike the mainframe systems of the day that were nearly always shared among diverse users. Today the PDP-8 is generally regarded as the first minicomputer. The PDP-8 spawned a cousin, the PDP-12, which merged data acquistion and display capabilities developed with the NIH-sponsored LINC computers into the PDP-8 architecture.

36-bit computers

For larger scientific problems DEC produced first the PDP-6 in 1964, using a 36-bit architecture. Using the same word length of the IBM 701-7094 series, which was being replaced by the 32-bit IBM 360 series, provided an alternative growth path for scientific customers. The successor was the PDP-10 series, eventually being sold as the DECsystem-10 and DECSYSTEM-20.

8-bit computers

The VT180 (codenamed "Robin") was a VT100 terminal with a Z80-based microcomputer running CP/M. This evolved into the Rainbow-100, which had both Z80 and 8088 CPUs and was capable of running CP/M, CP/M-86, and PC-DOS.

16-bit computers

Another of the famous machines in the PDP series was the PDP-11, which, following an industry trend for 8-bit bytes, used a 16-bit word. PDP-11 machines started in the market essentially as upscale PDP-8s, but as improvements to integrated circuits continued, they eventually were packaged in cases no larger than a modern PC.

The PDP-11 systems supported several operating systems of the day, including Bell Labs' new UNIX operating system as well as DEC's RSX and RSTS. Both RSTS and UNIX were available to educational institutions at little or no cost, and these PDP-11 systems were destined to be the sandbox for a generation of engineers and computer scientists.

The PDP-11's 16-bit, byte-oriented architecture provided a 64KB virtual address space. Most models had a paged physical memory architecture and memory protection features to allow timesharing, and some could support split Instruction & Data spaces for an effective virtual address size of 128KB and a physical address size of up to 4MB.

VAX Computer series

In 1976 DEC decided to move to an entirely new 32-bit platform, which they referred to as the super-mini. They released this as the VAX (Virtual Address eXtension) 11/780 in 1978, and immediately took over the vast majority of the minicomputer market. Desperate attempts by competitors such as Data General (which had been formed in 1968 by a former DEC engineer who had worked on a 16-bit design that DEC had rejected) to win back market share failed, due not only to DEC's successes, but the emergence of the microcomputer and workstation into the lower-end of the minicomputer market. In 1983, DEC cancelled their "Jupiter" project, which had been intended to build a successor to the PDP-10, and instead focused on promoting the VAX as their flagship model.

The VAX series had an instruction set that is rich even by today's standards (as well as an abundance of addressing modes). In addition to the paging and memory protection features of the PDP series, the VAX supported virtual memory. The VAX could use both Unix and DEC's own VMS operating system.

At its peak in the late 1980s, Digital was the second-largest computer company in the world, with over 100,000 employees. It was during this time that they appeared to gain a feeling of invincibility, and branched out into software, producing products for almost every then "hot" niche. This included their own networking system, DECnet, file and print sharing, relational database, and even transaction processing. Although many of these products were well designed, most of them were DEC-only or DEC-centric, and customers frequently ignored them and used 3rd party products instead. This problem was further magnified by Olsen's aversion to advertising and his belief that well-engineered products would sell themselves. Hundreds of millions of dollars were spent on these projects, at the same time that workstations based on RISC architecture were starting to approach the VAX in performance. Blinded by their own success of the VAX/VMS products which followed the proprietary model, the company executives would later be blind-sided by commodity hardware in the form of Intel-based personal computers and standards-based software such as unix and Internet protocols such as TCP/IP. In the early 1990s DEC "suddenly" found its sales faltering, and DEC's first layoffs followed.

In 1990 DEC was about to launch a new generation of computer disk drives into the marketplace. Code named the RA-90, it was the second largest development project ever undertaken by the company. Several major technological innovations were to be simultaneously integrated into this state of the art (at the time) product. Unfortunately, because of product design glitches, the RA-90 was very late in coming to market. By the time enough glitches had been resolved to allow limited shipments, competitors had released enhanced technology drives at much lower prices. What could have been a huge win for this organization became a great failure.

Their response was to design a single microprocessor with 64-bit RISC architecture (as opposed to the 32-bit CISC architecture used in the VAX) that could be used both in the servers, as well as a workstation line of their own. The result was the Alpha processor, which held the performance crown into the 2000s. The Alpha-based computers (AlphaServer) were able to run VMS, Unix and Microsoft's new server operating system Windows NT. DEC also tried to compete in the Unix market by marketing the VMS operating system as "OpenVMS" and by selling their own Unix (OSF/1, later renamed to Digital Unix and then renamed again to Tru64), and it began to advertise more aggressively. DEC was simply not prepared to sell into a crowded Unix market however, and furthermore the low end PC-servers running NT (based on Intel processors) took marketshare from Alpha-based computers. DEC's workstation and server line never gained much popularity beyond former DEC customers.

Closing DEC's Business

Ken Olsen was replaced by Robert Palmer as the company's CEO, but Palmer was unable to stave the tide of red ink and more rounds of layoffs ensued. DEC's database product was sold to Oracle, and its high-end Storageworks disk unit sold to Quantum. In May 1997 DEC sued Intel for allegedly infringing on its Alpha patents in designing the Pentium chips. A settlement reached in DEC's favour included sale of DEC's chip business to Intel. About the same time its networking business was sold to Cabletron, and eventually the company itself was sold to Compaq on January 26, 1998. Compaq itself was taken over by Hewlett-Packard in 2002.

The Digital logo survived for a while after the company ceased to exist, as the logo of Digital GlobalSoft, an IT services company in India (which was a 51% subsidiary of DEC). Digital GlobalSoft was later renamed "HP GlobalSoft", and no longer uses the Digital logo.


Digital supported the ANSI standards, especially the ASCII character set, which survives in Unicode and the ISO character set. Digital's own Multinational Character Set also had a large influence on the Latin-1 characters in ISO 8859-1 and Unicode.

The first versions of the C programming language and the UNIX system ran on Digital's PDP series of computers (first on a PDP-7, then the PDP-11's), which were the first commercially viable minicomputers.

Digital also produced the popular VAX computer family, the Alpha (AXP) microprocessor, the first commercially successful workstation (the VT-78), and some commercially unsuccessful personal computers.

Digital produced top-line operating systems, like OS-8, TOPS-10, TOPS-20, RSTS/E, RSX-11, RT-11, and VMS. PDP computers, in particular the PDP-11 model, inspired a generation of programmers and software developers. Some PDP-11 systems more than 25 years old (software and hardware) are still being used (as of 2004) to control and monitor factories, transportations systems and nuclear plants. Digital was an early champion of time-sharing systems, as anybody who has used other operating systems like MVS or VM/CMS from IBM can attest.

Digital was to the command-line interface (CLI) what Apple was to the GUI: there was history before and innovation after, but it was Digital's OSes that put it together in a complete and definitive form. The command-line interfaces found in the Digital's OSes, eventually to be codified as DCL, would look familiar to any user of modern microcomputer CLI's; those used in earlier systems, such as CTSS, IBM's JCL, Univac's time-sharing systems, would look utterly alien. Many features of the CP/M and MS-DOS CLI show a recognizable family resemblance to Digital's OSes, including command names such as DIR and HELP and the "name-dot-extension" file syntax.

VAX and Micro-VAX computers (very widespread in the 1980s) running VMS formed one of the most important pre-Internet networks, DECnet, which mixed business and research facilities. The DECnet protocols formed one of the first peer-to-peer networking standards.

Digital was one of the major champions of ethernet. For multiple generations of computers, ethernet controllers from Digital were de facto standard components on many computer boards.

Clustering, an operating system technology which treated multiple machines as one logical entity was invented by Digital. This technology was the fore-runner to systems like Network of Workstations which are used for massively cooperative tasks such as web-searches and drug research.

The VT-100 computer terminal became the industry standard and even today terminal emulators such as hyperterminal and Xterminals follow that standard.

The X Window System, the first remote-windowing system, was developed by Project Athena at MIT. Digital was the primary sponsor for this project.

Dave Cutler, the operating system guru who led the development of RSX-11M, RSX-11M+, VMS and then VAXELN left Digital in 1988 to lead the development of Windows NT. There have been much rumors/jokes that WNT=VMS+1 (increment each letter by one).

Notes-11 and its follow-on product, VAXnotes were two of the first examples of online collaboration software, a category that has become to be known as groupware. Len Kawell, one of the original Notes-11 developers later joined Lotus Development Corporation and contributed to their Lotus Notes product.

Digital was one of the first commercial businesses connected to the Internet, ( being one of the first of the now ubiquitous .com domains.

The popular AltaVista, created by Digital, was one of the first comprehensive Internet search engines (although Lycos was earlier, it was much more limited).


  • "DEC used by Digital itself:" PDP11 Processor Handbook (1973): page 8, "DEC, PDP, UNIBUS are registered trademarks of Digital Equipment Corporation;" page 1-4, "Digital Equipment Corporation (DEC) designs and manufacturers many of the peripheral devices offered with PDP-11's. As a designer and manufacturer of peripherals, DEC can offer extremely reliable equipment... The LA30 DECwriter, a totally DEC-designed and built teleprinter, can serve as an alternative to the Teletype."
  • Edgar H. Schein, Peter S. DeLisi, Paul J. Kampas, and Michael M. Sonduck, DEC Is Dead, Long Live DEC: The Lasting Legacy of Digital Equipment Corporation (San Francisco: Barrett-Koehler, 2003), ISBN 1-57675-225-9.

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