... allow Are ... Ouch, you're straining dead neurons.... As the KMC-11 Development Tools developer for RSX-11M and VMS, I know it's possible. I just don't remember the all the hoops we jumped through to do it. (this was circa 1978/79) The basic approach required us to map the IO registers and peek and poke values in the registers to control execution. Of course this was all written in MACRO-11, not un-manly FORTRAN. ;^) You probably had to be an RSX admin user ( UID below [10,*] ) to run the tools (loader and debugger). On VMS I had to learn the very new facility (I don't think it was in V1.0) of Page Frame Mapping and allocate a page map to get to UNIBUS IO space. This required a specific privilege too. I ported the tools code from Macro-11 to VAX Macro by doing semi- mechanical find/replace on the opcodes, and other tweaks. I even created a few macros to mimic the missing PDP-11 instructions, like SWAB. It needed very little needed rewriting to get working. Dave.