My first computer was a circa late-1970s RCA Cosmac VIP, that I programmed in machine language. With a CDP1802 microprocessor and sixteen 16-bit registers it would do about 100,000 instructions per second.
I filled one of the Cosmac's expansion I/O slots with a circuit board that I interfaced to a Paia Electronics "drum board kit" that I assembled. After writing a program on the Cosmac, I had a programmable "drum machine". I could key the sequence I needed the drum machine to play back from the Cosmac keyboard and then record the resulting drum track on a 4-track Teac reel to reel tape machine either as drum tracks or simple click tracks.
This was back in the Dark Ages before MIDI came out (in 1983). In those days, if you wanted to do much of anything in electronic music without spending several thousand for a Moog, you ended rolled your own devices.

I filled one of the Cosmac's expansion I/O slots with a circuit board that I interfaced to a Paia Electronics "drum board kit" that I assembled. After writing a program on the Cosmac, I had a programmable "drum machine". I could key the sequence I needed the drum machine to play back from the Cosmac keyboard and then record the resulting drum track on a 4-track Teac reel to reel tape machine either as drum tracks or simple click tracks.
This was back in the Dark Ages before MIDI came out (in 1983). In those days, if you wanted to do much of anything in electronic music without spending several thousand for a Moog, you ended rolled your own devices.