I've never really understood the purpose of the turbo button.

If it makes your computer faster, why not have it on all the time?
If it doesn't make it faster, then what's the point?

However, after exhaustive research, I have discovered its true meaning.
Back in the old days when processor speeds would double at insane rates, software wouldn't pay any attention to the speed of the processor. If you had that fancy new Pentium 133 and you tried to run a game written a few years ago for a 286 it would run much too fast.

So, you turn the turbo off. Voila, instant slowdown.

These days, software is smarter (or claims to be), and if you even have a turbo button on your computer casing, it probably isn't hooked up to anything.

Not only did turbo buttons serve a very minor purpose (slowing the machine down so you could play "dumb" games at a sensible speed), on most of them, the numbers they displayed wasn't even measured.

The "turbo" function was provided on the motherboard. There was a 3 pin connector, and the turbo button connected (usually) the centre pin to one of the two outside pins when pressed, and to the outside pin when released.

So how did we get the nice cool numbers to display? Jumpers. A whole load of them in the case. And you had to set for every segment in the seven segment display whether it should be off (no jumper), on when in turbo mode, on when in slow more, or on when in both. This was often done with 4 pins arranged in a small "T" shape. The common pin was the top-middle, and you connected the jumped left, right or down for the three options.

Towards the end of the craze of turbo buttons, some motherboards progressed to where you could configure the display in the BIOS setup screens.

Either way, it was up to the person who built the machine to decide what numbers to display. Most common was the clock speed that the machine ran at when in each mode (from the motherboard documentation), or the Landmark speed rating (measured by a piece of software once the machine had been fully built).

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