A number guessing game on the PDP-7's teletype. It was written for this cabinet in 2026, not found in an archive: it is here to exercise the keyboard and teleprinter, which the period programs on the menu hardly touch. Hi-lo was one of my first programs.
Play. Click the teletype paper so it has the keyboard.
- Press Return. HILO answers I HAVE ONE.
- Type a guess and Return. It says HIGHER, LOWER or RIGHT, with the number of guesses.
A lucky game:
GUESS? 50
LOWER.
GUESS? 25
RIGHT. GUESSES: 2
The number is a counter that runs from 0 to 99 while HILO waits for your Return, so your timing picks it. Halving finds any number in seven guesses.
The teletype is half duplex, as a KSR-33 on a PDP-7 was: what you type is printed by the teletype itself, not echoed by the program. LOCAL COPY under the paper is that switch; turn it off and the paper shows only what HILO prints.
Demo reboots and lets a scripted operator play one game by halving. The readout is the guess count, read from the program's variable tries. Memory, source view, is hilo.s with 👉 on the line running; while it waits for a key, that is the loop polling the keyboard.