DEC Professional
| Industry | Computer hardware |
|---|---|
| Founded | May 16, 1957 |
| Headquarters | Maynard, Massachusetts , United States |
| Products | Professional 325, Professional 350, Professional 380 microcomputers |
The Professional 325 (PRO-325), Professional 350 (PRO-350), and Professional 380 (PRO-380) are PDP-11 compatible microcomputer models introduced by Digital Equipment Corporation (DEC) as premium alternatives to the IBM PC. The Pro-325 and Pro-350 debuted in 1982, with the Pro-380 following in 1985.
History
Resembling the Rainbow 100 and DECmate II in design, the PRO lineup incorporated the LK201 keyboard alongside 400KB single-sided quad-density floppy disk drives (RX50), offering users a choice between color or monochrome displays.
Although technically advanced—such as DEC’s 22-bit addressing capability that allowed access to up to 4MB of memory compared to the Intel 8088’s 1MB limit—the PRO series struggled to attract a substantial market share. The computing sector quickly converged on Intel 8088-based IBM PC compatible systems due to their wider software ecosystem. For example, BYTE magazine reported in 1984 that Venix performed more efficiently on IBM PCs than on either the DEC Professional or PDP-11/23 platforms.
A major obstacle was the scarcity of cost-effective small business software tailored for PDP-11 architectures. While numerous CP/M applications were straightforwardly adapted for 8086/8088 processors and MS-DOS, porting PDP-11 software to the PRO was complicated by partial incompatibilities with its predecessor line—a move likely intended by DEC to shield its lucrative minicomputer segment from competition posed by lower-priced PCs.
The PRO series failed to establish a significant presence within office environments or scientific workstation markets, both of which predominantly favored systems powered by Intel 8086 or Motorola 68000 CPUs. DEC’s inability to break into the mainstream PC market signaled a downturn for New England’s computer hardware industry, historically led by minicomputer pioneers such as DEC, Data General, Wang, Prime, Computervision, Honeywell, and Symbolics.
Technical specifications
The PRO-325 and PRO-350 models utilize the F-11 chipset—the same found in LSI-11/23 systems—to implement a single-board PDP-11 architecture featuring up to six expansion slots connected via a proprietary CTI (Computing Terminal Interconnect) bus with 90-pin ZIF connectors. Both models come equipped with dual RX50 floppy drives; while the PRO-325 depends exclusively on floppy storage, the PRO-350 and PRO-380 include an internal hard disk. Unlike typical PDP-11 machines that connect separate serial terminals, the PRO line integrates built-in bit-mapped graphics, combining console and display functions into one unit.
Input/output components within the PRO series differ markedly from those found in standard PDP-11 hardware. Although the internal bus supports direct memory access (DMA), none of the offered I/O devices take advantage of this feature. The interrupt handling system is based on Intel PC chips rather than adhering to traditional PDP-11 architecture. This divergence necessitates significant operating system modifications to support the PRO family, rendering unmodified PDP-11 software incompatible without adaptation.
The standard operating system for the PRO-3xx series is DEC's Professional Operating System (P/OS), a variant of RSX-11M enhanced with a menu-driven user interface. Industry reviewers criticized this interface as cumbersome and slower compared to the command-line MS-DOS interfaces gaining traction during that period.
Additional operating systems supported include DEC’s RT-11, VenturCom’s Venix, and 2.9BSD Unix.
The Professional 380 (PRO-380) introduced the more advanced J-11 chipset, also utilized in 11/73 systems. However, due to motherboard clock constraints, the J-11 operated at only 10 MHz instead of its typical 16–18 MHz range, resulting in performance inferior to a standard 11/73.
A specialized variant, the DEC Professional Series PC-38N, is based on the PRO-380 and includes a real-time interface (RTI) functioning as the system console for the VAX 8500 and 8550. This RTI incorporates two serial line units—one dedicated to connecting with the VAX environmental monitoring module (EMM), while the other facilitates data communication. It also features a programmable peripheral interface (PPI) comprising three 8-bit ports designed for exchanging data, address signals, and control information between the console and VAX console interface.
Graphics
At the time, the Pro series offered cutting-edge graphics capabilities. The graphics card in the Pro 325/350 was equipped with 32 KB of RAM, enabling two-color output at resolutions of 1024x240 pixels at 60 Hz or 1024x256 pixels at 50 Hz. It supported rendering either 512 pixels per line with four intensity levels or 256 pixels per line with sixteen intensity levels; however, typical applications primarily utilized the 1024x240 resolution and addressed only 960 of the available 1024 horizontal pixels.
To achieve color display, an additional graphics card containing 64 KB of RAM was necessary. This expansion allowed for eight colors per pixel selected from a palette of 256 colors in mapped mode, which was the standard for most software. An alternative unmapped mode permitted up to 4096 simultaneous colors at a resolution of 256 pixels per line or 64 colors at 512 pixels per line by varying intensity levels applied to base colors.
The Pro 380 model enhanced these features by integrating a graphics card with 128 KB of memory, supporting interlaced display modes that effectively doubled vertical resolution. There was also an optional color supplement card with 256 KB of RAM, enabling the use of a 4096-color palette in mapped mode. The video memory of the Pro 380 was capable of storing four uninterlaced frames or two interlaced frames simultaneously.
Clones
Continuing the tradition established by PDP-8 and PDP-11 systems, the Professional 350 was replicated by Elektronika within the Soviet Union.
Additional significant clones of the PDP-11 include:
- Elektronika 60
- (also referred to as Elektronika MS-0585)
External links
- Pro 325, 350, 380
- The Observation Deck: UNIX, circa 1984
- The Xhomer, a DEC Pro emulator based on SIMH/PDP-11
- DEC's PC Challenge 1982, a corporate documentary detailing DEC's development of the Professional 325, Professional 350, and Rainbow 100 following IBM's PC introduction