Apple - 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 "6-key rollover with USB, N-key rollover with USB to PS/2 adapter". When using it with USB on my Mac, I've confirmed that is in fact 20-key rollover.

My Apple Wireless Keyboard and the keyboard on my MacBook Air seem to allow pressing all combinations of two keys at the same time, but not some combinations of three keys. So I guess they are 2-key rollover.

Another way to test it is to open the keyboard viewer from the input menu or with open -a KeyboardViewer.

Apple Macbook Pro's are 6 Key Rollover, looks like limitation of USB

Hold keys 1 2 3 4 5 6 and then 7, 7 does not register