All, I've got the original PDP-7 cat working in my PDP-7 user-mode simulator called "a7out". The cat.s source code and the a7out program are in the Github repository in src/cmds and tools, respectively. The repository is at https://github.com/DoctorWkt/pdp7-unix The mailing list is at http://minnie.tuhs.org/pipermail/pdp7-unix/ I'm attaching the a.out assembly output as the as7 assembler in the repository currently is not quite ready for cat.s. To run the original cat, create a text file, e.g. echo hello > file1 $ ./a7out a.out file1 hello <- the output of the PDP-7 machine code Cheers, Warren P.S Thanks again to Norman for getting us the scans.