Putting a PDP11 on a S100 card using T11 is easy. Its a T11 32KW (32kx16) of ram,small rom 1k for monitor), and minimally two serial ports that are DL compatable and demuxing the bus for the IO page to put on the s100 bus. There is no need to memory access on s100 as 32KW is the max memory for that cpu without creating a copy of the KT11 MMU. The only reason to put IO on the bus is for peripherals but interrupts on S100 are not handled in a way that is compatible with T11 (T11 when an interrupt request comes in expects a 8bit vector on the low data bus as a pointer to interrupt handlers similar to Z80 mode 2 but very different timing). The problem is the mass storage driver has to be created for at least RT11OS. Porting CUBIX (6809 source) may be possible as the PDP11 and 6809 are similar. To do any OS work a PDP11 (real or SIM) is needed. Of course the easy way to do that is get a DEC falcon card (SBC11) and a Memory card and you have that and more. Same for the F11 capu or J11. Board for Qbus exist, Qbus systems are small and interesting in their own right and S100 IO is very foreign compared to DEC standard hardware. They only "build it" that would make any sense if any is putting a T11 on a single board with max ram, some rom (monitor), DL compatable IO (basically UARTs) and a CF. That would run RT11 if someone could create the disk driver and loading it for the first time is covered by using a serial line and TU58(block addressable tape) simulator or the real thing is on hand. without the disk driver if the serial is truely DL compatable then the board could run RT11 out of the box with the DD driver (tu58 tape or an emulator of that). IT is possible to do a MT11 MMU with T11, it's a bit of hardware and has to be interconnected to the interrupt system as the MMU also implements memory protection via exceptions(interrupts). With that larger software is "possible" but it's a lot of hardware and the T11(a minimum PDP11) is not a expanded/full PDP11 with I&D spaces or floating point. if you do not understand the difference then find and read the DEC Microcomputer Processor Handbook" as it answers most if not all the questions. The only DEC OS most know is RT11 which is like CP/M. The fancier OSs like RSTS and RSX (timesheare and multitasking) are out of reach of the T11 due to memory/MMU. IF you want those OSs get a SIM, Qbus box you will get to working but with more effort is you have never worked with DEC systems/hardware. Also RT11 is the only one available (wink/nod) for strict hobbiest use. If one wanted to go the fully home brewed OS route I'd suggest CP/M as a pattern (CPM 68K is in C and can be compiled for PDP11), maybe a uClinux port but it will have to add virtualization via swapping (remember 32KW memory). Summary is I'm both DEC and S100 and putting PDP11 on S100 is a poor idea. S100 works for CPUs based off 8080 but with increasing overhead for bending their control signals to meet IEEE696. For a lot of micros it is a hard mismatch and the conventions of 8080/8085/z80 world makes S100 generally odd to most other CPUs. For example 6502, 6800, 6809, T-11 and others ALL depending on memory mapped IO, something generally uncommon on s100. I've built up a T11 SBC and with out a disk driver (on my long round toit list) its fairly useless save for an SBC. Compared to my small Qbus system with 11/23+ CPU, 1MB ram 4 serial ports, RQDX3 floppy/hard disk and a Ethernet NIC, the T11 SBC is a toy on the scale of the 8085 or 6100 sampler SBCs. The difference is the real PDP11 runs serious OSs (RT11, RSTS, RSX and unixV6) and can do even by current standards real work(spreadsheets, languages, editors, compilers and assemblers). So the PDP11 on S100.. don't. Allison