[acdha]

More accurately, it was real on earlier hardware when people had things like games which were unusable on processors faster than IBM’s original 4.77MHz 8086 processor. As a kid I had a hand-me-down system where that was definitely necessary for a handful of older games.

That meant almost every case had that button and people got used to it. That didn’t mean it was always connected - we’re talking a simple cable connecting to a couple of pins on the motherboard so this was trivial - and I knew a couple of people who disconnected it to keep kids or certain hopeless adults from clicking it, forgetting, and then complaining that the computer was slow.

By the late 386/486 era that’d become pretty common and you stopped seeing it as much.