What composers did once they knew the limits

Writing a theme people can hum after one hearing

Koji Kondo's Super Mario Bros. and Legend of Zelda scores are built for repetition at length without fatigue, which is a harder constraint than melody.

Atmosphere out of a chip that had none

Hirokazu Tanaka's Metroid score uses the noise channel and detuned pulses to build unease rather than tune, which was not what the hardware was expected to do.

A chord on a machine with no chords

With one voice per channel, a chord has to be played as a very fast arpeggio — the sound everybody now recognises as chiptune.

The score people cite when they argue about the best

Mega Man 2 (1988) is the usual reference for what the chip could do once composers had five years of practice on it.