PC speaker
The IBM PC's tiny built-in beeper, a 1-bit source that clever programmers still coaxed into playing digital audio.
When the IBM PC arrived in 1981 it carried a plain speaker driven by the 8253/8254 timer chip — meant for square-wave beeps and nothing more. With pulse-width modulation you could nonetheless force out voices and sampled sound by flicking the single bit thousands of times a second on careful timing; Access Software's "RealSound" (1988) made it commercial. Music in early games and demos was born the same way. Quality was gritty and ate nearly all the CPU, and the trick became moot once AdLib and then the Sound Blaster brought real audio cards.