Are Apple keyboards multi-key rollover?
Current Apple keyboards (this answer is from 2012, but I've re-tested in 2020) are not N-Key rollover and as far as I know no recent keyboard they have ever made is. I think some of the really old ones were N-key rollover, but can't confirm it.
You can use this website to test your keyboard.
Beware that every keyboard has a different electronic layout and will fail in different key combinations. On my Apple Aluminium keyboard if I hold down the W and E keys, then press the D key, the third key press does not register. But there are other key combinations where as many as six keys will register at once.
It is commonly said that true N-Key rollover can only be achieved using a PS/2 keyboard, and that USB keyboards can only achieve 6-key rollover. As far as I know, this limitation only applies to Microsoft Windows.
My mechanical keyboard's spec sheet claims &quot;6-key rollover with USB, N-key rollover with USB to PS/2 adapter&quot;. When using it with USB on my Mac, I've confirmed that is in fact 20-key rollover.