hello world = H = hexadecimal

hex n.

1. Short for hexadecimal, base 16. 2. A 6-pack of anything (compare quad, sense 2). Neither usage has anything to do with magic or black art, though the pun is appreciated and occasionally used by hackers. True story: As a joke, some hackers once offered some surplus ICs for sale to be worn as protective amulets against hostile magic. The chips were, of course, hex inverters.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.