DEC Professional (computer)

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DEC Professional
Digital Equipment Corporation 1987 logo.svg
VAX Console.jpg
A DEC Professional used as a console for a VAX 8550
DeveloperDigital Equipment Corporation
Product familyProgrammed Data Processor
Release date1982; 40 years ago (1982)
Operating systemP/OS, RT-11, VenturCom, Venix, 2.9BSD Unix
InputLK201 keyboard
PlatformDEC 16-bit

The Professional 325 (PRO-325), Professional 350 (PRO-350), and Professional 380 (PRO-380) were PDP-11 compatible microcomputers introduced in 1982 by Digital Equipment Corporation (DEC) as high-end competitors to the IBM PC.


Like the cosmetically similar Rainbow 100 and DECmate II (also introduced at that time),[1] the PRO series used the LK201 keyboard and 400KB single-sided quad-density floppy disk drives (known as RX50[2]), and offered a choice of color or monochrome monitors.

For DEC, none of the three would be favorably received,[citation needed] and the industry instead standardized on Intel 8088-based IBM PC compatibles which were all binary program compatible with each other. In some ways, the PDP-11 microprocessors were technically superior to the Intel-based chips. While the 8088 was restricted to 1MB of memory because of its 20-bit address bus, DEC microprocessors were capable of accessing 4MB with their 22-bit addressing (although direct addressing of memory was limited in both approaches to 64KB segments, limiting the size of individual code and data objects). But other factors would weigh more heavily in the competition, including DEC's corporate culture and business model, which were ill-suited to the rapidly developing consumer market for computers.[citation needed] BYTE in 1984 reported that Venix on the PC outperformed the same operating system on the DEC Professional and PDP-11/23.[3]

Further, although the PDP-11 was a very successful minicomputer, it lacked a wide base of affordable small business software. By comparison, many existing CP/M applications (see the Rainbow 100) were easily ported to the similar 8086/8088 chips and MS-DOS operating system. Porting existing PDP-11 software to the PRO was complicated by design decisions that rendered it partially incompatible with its parent product line. Industry critics observed that this incompatibility appeared at least in part deliberate, as DEC belatedly sought to "protect" its more-profitable mainstream PDP-11s from price competition with lower-priced PCs.[citation needed]

The PRO was never widely accepted as an office personal computer, nor as a scientific workstation, where the market was also headed to Intel 8086, or alternately to Motorola 68000-based computers. The failure of DEC to gain a significant foothold in the high-volume PC market would be the beginning of the end of the computer hardware industry in New England, as nearly all computer companies located there were focused on minicomputers for large organizations, from DEC to Data General, Wang, Prime, Computervision, Honeywell, and Symbolics Inc.[citation needed]

Technical specifications[edit]

DEC "Fonz-11" (F11) Chipset

The PRO-325 and -350 used the F-11 chipset (as used in LSI-11/23 systems) to create a single-board PDP-11 with up to six expansion slots[4] of a proprietary CTI (Computing Terminal Interconnect) bus using 90-pin ZIF connectors. The PRO family used dual RX50 floppy drives for storage; the PRO-325 had only floppies, and the 350 and 380 also included an internal hard drive. Mainline PDP-11s generally used separate serial terminals as console and display devices; the PRO family used in-built bit-mapped graphics to drive a combined console and display.

All other I/O devices in the PRO family were also different (in most cases, radically different) from their counterparts on other PDP-11 models. For example, while the internal bus supported direct memory access (DMA), none of the available I/O devices actually used this feature. The interrupt system was implemented using Intel PC chips of the time, which again made it very different from the PDP-11 standard interrupt architecture. For all these reasons, support of the PRO family required extensive modifications to the previously-existing operating system software, and the PRO could not run standard PDP-11 software without modification.

The default PRO-3xx operating system was DEC's Professional Operating System (P/OS), a modified version of RSX-11M with a menu-driven core user interface.[4] Industry critics complained that this user interface was awkward, slow, and inflexible, offering few advantages over the command-line based MS-DOS user interface that was coming into widespread use.[citation needed]

Other available operating systems included DEC RT-11, VenturCom Venix, and 2.9BSD Unix.

DEC "Jaws-11" (J11) Chipset

Later, the Professional 380 (PRO-380) was introduced using the much faster J-11 chip set (as used in 11/73 systems). However, due to clocking issues on the motherboard, the J-11 chip ran at 10 MHz instead of 16-18 MHz, thus making the PRO-380 slower than a stock 11/73 system.

The DEC Professional Series PC-38N was a PRO-380 with a real-time interface (RTI) that was used as the console for the VAX 8500 and 8550. The RTI has two serial line units: one connects to the VAX environmental monitoring module (EMM) and the other is a spare that could be used for data transfer. The RTI also has a programmable peripheral interface (PPI) consisting of three 8-bit ports for transferring data, address, and control signals between the console and the VAX console interface.[5]


Like the PDP-8 and PDP-11 before it, the Professional 350 was cloned by Elektronika in the Soviet Union.

Other PDP-11 clones:


  1. ^ "PCs (1982)". Digital Computing Timeline. Digital Equipment Corporation. 30 April 1998. Retrieved 21 Jan 2016.
  2. ^ The RX50 FAQ
  3. ^ Hinnant, David F. (Aug 1984). "Benchmarking UNIX Systems". BYTE. pp. 132–135, 400–409. Retrieved 23 February 2016.
  4. ^ a b Melling, Wesley (June 1983). "Digital's Professional 300 Series / A Minicomputer Goes Micro". BYTE. pp. 96–106. Retrieved 5 February 2015.
  5. ^ VAX 8500/8550 System Hardware User's Guide. Digital Equipment Corporation. 1986. pp. 1–8.

External links[edit]