For people who type with many fingers, are Macintosh keyboards are multi-key rollover?
Bonus points for explaining how to test this on any Mac or listing which models are 3 key rollover or higher.
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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
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.
As someone who has built a Hackintosh (a computer that is made of standard, off the shelf PC components, but runs Mac OS), I can confirm that Apple's laptops use a PS2 interface. Among the many .kext files that the custom boot loader can install are PS2 drivers. These allow the use of PS2 keyboards and mice with Mac OS, but are derived from .kexts that are used by Apple's laptops.
I just wanted to add on some information as to why certain combinations of keys don't register on Apple keyboards. I don't remember in which technical paper I read it in, it would have been at least 10 years ago now, but when Apple unveiled their keyboard (I think the one in 2003?) they said it contained certain protections in case a pet walked over it.
This is what's happening. There is a special rule built-in that ignores input in the name of pet-detection. If you press at least two keys in the same column, additional keypresses in the whole row of those keys are ignored. And if you press keys that would activate this blocking mechanism while you have keys already pressed, they are ignored too. This means you can press "1QAZ" and not be able to input anything else while holding those keys down.
In conclusion Apple keyboards have a 4-key rollover on columns (not counting spacebar and function keys), and 6-key on rows, if a row is not locked by another key, which technically makes it 2-key rollover. Thank the Apple engineers. Oh and since the keyboards use a PS/2 interface this limitation is completely arbitrary and the modifier keys do not affect this keyboard locking at all, so you can press 10 keys at once just fine (shift, ctrl, alt, cmd, and any six keys on the same row).
Hope this helps someone in the future.
I was surprised to see that the keyboard on the Macbook Pro can pass my quick keyboard test. However, Apple's external USB keyboards miss keypresses doing my simple test below.
I typed out "The quick brown fox jumps over the lazy dog" while holding down both SHIFT keys. Perhaps the internal keyboard has a fancy hook up that isn't USB.
Sometimes it is not enough to simply ask yes-or-no about a complex feature like NKRO. Often the answer is, "It depends..." Several above commenters suggested holding down
d, to see if the
d key registers. On the built-in keyboard of my MacBookPro 2015, that "fails." But what succeeds is a more common 3-key sequence:
E (arguably a more commonly-typed sequence, e.g. in the word
DEBUG :) ) BUT, my "cheapo" (MacAlly) external USB keyboard fails to register the
E if I already have
D held down. My "expensive/gaming" (CoolerMaster) can register all characters in "DEBUG" held down simultaneously.