[avmich]

> make viruses in one word of memory

OT, but with PDP-11 you could write 103737 (in octal), which propagated across memory (backwards).

10 means "move", first 37 means "from what R7 is pointing to, autodecrementing R7 before copying", second 37 is "to what R7 is poiting to, autodecrementing R7 before copying". R7 is the program counter, so this operation was copied one word (16 bits) before the executing instruction and then control was passed to that new word.

Of course, with GA144 you can have up to 4 commands in a single 18-bit long instruction, so opportunities are better...