to implement the memory management unit. An Intel i960 processor was used to load the microcode, perform floating point (in IEEE format) and provide ODT. The 4 DLARTs of the earlier M100 were emulated on a single Xilinx part. All of the memory (both microcode and PDP-11 main memory) was implemented using SRAM. While not of any significant effect in the field it suffered from the fact that it used a large number of microcode controlled drivers onto tri-state buses, which made developing microcode somewhat hazardous. The M11 design was implemented in VHDL and fully simulated using Mentor Graphics QuickSim II with behavioural language models for both the Q-Bus and console UART. It ran patched versions of the Digital PDP-11/23 CPU diagnostics on the simulator before any hardware was constructed. M1 The M1 was a processor upgrade board, done as an ASIC re-implementation of the M11's implementation of the PDP-11 instruction set. Despite being an ASIC implementation it was also fully microcoded. The M1 used an Atmel 0.85 μm ASIC for 5V operation. PDP-11 operating systems RSX-11 Ownership of RSX-11S, RSX-11M, RSX-11M Plus and Micro/RSX was transferred from Digital to Mentec Inc. in March 1994 as part of a broader agreement. In 2006 Mentec Inc. was declared bankrupt while Mentec Ltd. was acquired by Irish firm Calyx in December 2006,. The PDP-11 software, which was owned by Mentec Inc. was then bought by XX2247 LLC, which is the owner of the software today. It is unclear if new commercial licenses are possible to buy at this time. Hobbyists can run RSX-11M (version 4.3 or earlier) and RSX-11M Plus (version 3.0 or earlier) on the SIMH emulator thanks to a free license granted in May 1998 by Mentec Inc. Legal ownership of RSX-11A, RSX-11B, RSX-11C, RSX-11D, and IAS never changed hands; therefore it passed to Compaq when it acquired Digital in 1998 and then to Hewlett-Packard in 2002. In late 2015 Hewlett-Packard split into two separate companies (HP Inc. and Hewlett Packard Enterprise), so the current owner cannot be firmly established. New commercial licenses have not been issued at least since October 1979 (RSX-11A, RSX-11B, RSX-11C) or 1990 (IAS), and no one of these operating systems was ever licensed for hobbyist use. RSTS In 1997 Digital and Mentec granted anyone wishing to use RSTS 9.6 or earlier for non-commercial, hobby purposes a no-cost license . The license is only valid on