While archiving a bunch of old 8 inch disks I found disks that apparently contain an old RSX11S system. I think it has been used in some kind of railroad CTC system. https://dl.dropboxusercontent.com/u/96935524/Datormusuem/PDP11RX01DISKS/DIS… It is possible to boot this image in SimH (when setting CPU type to 11/03, 11/23 (F11), 11/34 or 11/73 (J11) ) I get this: sim> b rx0 XDT: 18 XDT>g RSX-11S V02 BL18 DEVICE TT01: NOT IN CONFIGURATION DEVICE FT00: NOT IN CONFIGURATION MCR -- 1 MCR -- 1 MCR -- 1 So first there is a XDT> prompt. By pressing g or p it starts RSX11S. But it seems to be possible to do other things. Commands like "s" and "l" do stuff "x" causes: XDT>x SYSTEM CRASH AT LOCATION 025276 REGISTERS R0=000000 R1=177170 R2=003403 R3=157000 R4=012422 R5=000002 SP=157004 PS=000340 SYSTEM STACK DUMP LOCATION CONTENTS 157004 157150 HALT instruction, PC: 000572 (MOVB #15,R2) sim I understand that RSX11S is a scaled down version of RSX11M. An embedded RTOS of that day. But what kind of commands are possible at the XDT and MCR(?) prompts. I am a little bit curious to understand more about the system that it has been running. /Mattis