The Macintosh computer (and the legacy-free iMac) paved the way for the USB devices of today. However, one of the little ironies is that the Macintosh keyboard was not fully USB compliant until around the middle of 2000.

If you plug in a Macintosh keyboard to a Windows machine, you will blue screen the computer, if you press the power button. This is because the USB implementation on a Macintosh involves dropping the fourth pin low to turn on the machine. This signal, which is out of spec for USB, is not handled by many drivers, including that of Windows 2000 RTM. The low fourth pin tells the Macintosh to come out of sleep mode, or to turn on or off.

I learned this because the keyboard drivers that I worked on were for a fully USB compliant board, as are the million other USB keyboards out there. In the old ADB system, Apple had two pins for this purpose, one for turning on the computer, and one for turning off the computer. We discovered this because someone's Mac turned off, but never back on again with the button on that keyboard (but it worked with other boards; We finally took it apark with a multitester to find out why.) They controlled the technology, and thus did not have any problems getting it to work with what their users expect. Apple's innovation, which they did not adhere to. Finally, the USB committee got the them to fix up their keyboards, and now they do something in software for that key, or so I am told.