<Can you restrict an architecture like this? I've never heard of an <Interlectual Property case being based on the fact that the 2 products <(CPUs) run the same instruction set. DEC and oh I forget on PDP-8, NEC and intel on 8086/V20 and plenty more. <Also, be warned that if you're going to use FPGAs you have to use the <manufacturer's tools which are not going to be Open-Source, and which are <not going to run under Open-Source OSes. Several of us have moaned about Not all are restricted to one vendor. Just why bother. Now, if you really want to build a PDP-11 of any kind yank the t11 chip PDP-11 and it does run RT11 (assuming standard devices) as the falcon card does. If 64kb of addressing is not enough try building a mapper like most of the 11s have, a couple of 74189s should do. This is a nice 40 pin dip and not much hard to design with than z80 though the z80 never offered things like selectable 8/16bit bus or selectable start/restart addresses not to mention cycle and clock options. Performance is better than LSI-11 if memory runs without wait states. Creating the chip is half the task, putting it to work is the real fun. Allison