Mentec
| Company type | Private |
|---|---|
| Industry | Computer hardware, Computer software |
| Founded | 1978 |
| Headquarters | Ireland |
| Products | PDP-11 processors, single-board computers (M70, M71, M80, M90, M100, M11, M1), PDP-11 operating systems (RSX-11 variants) |
Mentec International Ltd, established in 1978, originally concentrated on software and systems for monitoring and control. It emerged as a prominent reseller and original equipment manufacturer (OEM) for Digital Equipment Corporation (DEC) in Ireland. Its branch, Mentec Computer Systems Limited, was responsible for repackaging PDP-11 processors, while the American division, Mentec Inc., targeted comparable markets. In the early 1980s, Mentec introduced remote terminal units based on the SBC/11-21 (Falcon).
After the introduction of the DEC J-11 PDP-11 processor chipset in 1982, Mentec developed its inaugural PDP-11 single-board computer, named the M70.
In 1994, DEC handed over PDP-11 operating systems to Mentec Inc., broadening its range of software offerings.
M70
Produced between 1982 and 1984, the M70 was a quad Q-bus module utilizing the J-11 chipset. It incorporated onboard ECC DRAM, bootstrap EPROMs, and featured four serial ports employing DEC DC319 DLART chips.
M71
Designed primarily for process control applications, the M71 provided options of 256 KB or 1 MB ECC DRAM, up to 512 KB of EPROM, four serial interfaces (DC-319 DLARTs), and two parallel ports via 8255 chips. This model was initially created to support Mentec's proprietary Remote Terminal Units.
M80
As an advancement of the M70, the M80 employed parity memory and operated at a higher clock frequency. It introduced software-based configuration through bootstrap mechanisms, which simplified hardware setup requirements.
M90
The M90 represented a clock-speed optimized variant of the M80 with incremental performance enhancements.
M100
The M100 was a redesign of the 11/93 board and marked Mentec’s final J-11 chipset-based processor board. Operating the J-11 chipset at 19.66 MHz, it included four integrated serial ports, memory capacities ranging from 1 to 4 MB, and an optional floating-point unit (FPU). The M100 offered a more efficient and faster version compared to its predecessor, the M90.
Subsequent iterations incorporated daughter cards featuring a Xilinx component replacing DLARTs and implementing FIFO buffers to prevent data overruns in OEM environments. Some versions also replaced onboard DRAM with SRAM daughter cards.
M11
The M11 was a microcoded PDP-11 instruction set implementation crafted entirely by Mentec as a processor upgrade board supplanting the M100. It utilized two Texas Instruments TI8832 ALUs—one dedicated to processing tasks and another managing memory—and a TI 8818 microsequencer. An Intel i960 processor managed microcode loading, IEEE floating-point calculations, and provided on-line debugging through ODT. The four DLARTs present on the earlier M100 were emulated within a single Xilinx chip; all memory was realized using SRAM. The design’s extensive use of microcode-controlled drivers on tri-state buses introduced complexity into microcode development.
Developed in VHDL and fully simulated using Mentor Graphics QuickSim II, the M11 successfully ran patched DEC PDP-11/23 CPU diagnostics on its simulator before hardware fabrication.
M1
The M1 was an ASIC-based processor upgrade card that reimplemented the M11’s microcoded PDP-11 instruction set. It featured an Atmel 0.85 μm ASIC operating at 5 V, delivering a more integrated design while preserving complete microcode programmability.
RSX-11
In March 1994, the rights to RSX-11S, RSX-11M, RSX-11M Plus, and Micro/RSX were transferred from DEC to Mentec Inc. Following Mentec Inc.’s bankruptcy in 2006 and the subsequent acquisition of Mentec Ltd. by the Irish company Calyx, the PDP-11 software rights were acquired by XX2247 LLC, which currently holds ownership. While the status of commercial licensing remains uncertain, enthusiasts are permitted to operate RSX-11M (version 4.3 or earlier) and RSX-11M Plus (version 3.0 or earlier) on the SIMH emulator under a complimentary license granted by Mentec Inc. in 1998.
The legal rights to RSX-11A, RSX-11B, RSX-11C, RSX-11D, and IAS stayed with DEC, which was acquired by Compaq in 1998 and then became part of Hewlett-Packard in 2002. After Hewlett-Packard's division into HP Inc. and Hewlett Packard Enterprise in 2015, the current ownership remains unclear. No new commercial licenses have been issued for these systems since at least October 1979 for RSX-11A/B/C or since 1990 for IAS, and these particular versions have never been authorized for hobbyist use.
RSTS
In 1997, DEC together with Mentec provided a free license allowing non-commercial hobbyist use of RSTS version 9.6 or earlier exclusively on the SIMH PDP-11 emulator. This permission also extends to certain other DEC operating systems and is included within officially sanctioned software packages available for download from the SIMH project website.