PDP-11 Binary that can execute on Unix and RT-11 ================================================ A binary executable image on PDP-11 Unix and RT-11 have headers that almost don't overlap. With care, a binary image can be created that can execute on either Unix or RT-11. The Unix header is the first 16 bytes, and immediately followed by the entry point. The RT-11 header is from &o40 to &o57 and specifies the entry point. With care, the first 256 bytes of a binary image can be written to allow the code to be loaded and executed on Unix or RT-11. With different entry points the code can then set things up internally so that the mainline code calls the appropriate system calls, TRAPs for Unix and EMTs for RT-11. UnixRT11 shows how the Unix and RT-11 headers compare and how to arrange them in a single binary to run on either Unix or RT-11. UnixRT.mac is a demo program that does this. This screenshot shows the same binary running on RT-11 and Unix. This is based on Paramucho's adaptation of the Hello Word demo program for the AsmPDP assembler.