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The Professional 325 (PRO-325), Professional 350 (PRO-350) 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), they used the LK201 keyboard and used 400kB single-sided quad-density floppy disk drives (known as RX50), and offered a choice of color or monochrome monitors.

Unfortunately for DEC, none of the three would be favorably received[citation needed], when the industry instead standardized on Intel 8088-based IBM PC compatibles which were all binary program compatible. In some ways the PDP-11 microprocessors were technically superior to the Intel device. While the 8088 was restricted to 1MB of memory because of its 20-bit address bus, DEC microprocessors were capable of addressing 4MB with their 22-bit addressing. 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 Digital's corporate culture and business model, which were ill suited to the rapidly expanding consumer market.

Further, although the PDP-11 was a very successful minicomputer, it lacked a base of affordable small business software. By comparison, many CP/M applications (see the Rainbow 100) were easily ported to the similar 8088 chip and MS-DOS operating system. Porting existing PDP-11 software to the Professional was complicated by design decisions that rendered it somewhat incompatible with its parent product line. It was never accepted as an office personal computer, or as a scientific workstation, where the market was also headed to Intel 8086 or Motorola 68000-based computers. The failure of DEC to gain a significant foothold in the volume PC market would be the beginning of the end of the computer industry in New England as nearly all computer manufacturers located there were focused on minicomputers, from DEC to Data General, Wang, Prime, Computervision and Honeywell[citation needed].

Technical specifications

The PRO-325 and -350 used the F-11 chipset (as used in LSI-11/23 systems) to create a relatively compact single-board PDP-11 with a limited number of proprietary expansion slots. The PRO family used RX50 floppies for storage; the PRO-325 only had floppies, the 350 and 380 also included internal hard drive. PDP11s generally used serial terminals as console and display devices; the Pro family used in-built bit-mapped graphics as their console. All other I/O devices on the PRO family were also different (in most cases, radically different) from their counterparts on other PDP-11 models. For example, while the bus supported direct memory access (DMA) none of the I/O devices used this feature. The interrupt system was done using Intel PC chips of the time, which again made it very different from the PDP-11 standard. For all these reasons, support of the PRO family required extensive modifications to the previous operating system software.

The default PRO-3xx operating system was DEC's Professional Operating System or P/OS, a modified version of RSX-11M with a menu-driven core user interface. Other available operating systems included DEC RT-11, VenturCom Venix, and 2.9BSD Unix.

Later, the Professional 380 (PRO-380) was introduced using the much faster J11 chip set (as used in 11/73 systems). A PRO-380 with the Real-Time Interface option was used as the console on high-end VAX-8800 family systems.

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