I was wondering about this! In all honesty I don't see any reason to go this low level, by doing this you're making it less portable. Ideally you want something like a stripped Linux or QNX system sitting on top of the hardware, with the system emulator sitting on top of that. If you want to avoid UNIX altogether, just take simh, and set it up so that it's started when the system boots, and you boot all the way up to the OS of your choice. Go one step further and hack simh so that if you shutdown the OS running on top of simh, that it shuts down the host OS. If you want to do hardware, go with FPGA's and reimplement the CPU and controllers like Neil Franklin is trying to do with the PDP-10. The tricky part here of course being the disk and tape controllers (unless you want to write your own device drivers). Zane