The built-in keyboard on PowerBook and iBook computers will not recognize more than two keys depressed simultaneously, with the exception of modifier keys. Some applications may require more than two keys be held down for certain functions.

PowerBook computers have always had keyboards that will not recognize more than two keys held down simultaneously; otherwise known as two-key lockout. Modifier keys, such as the option, command, or control, are not affected by two-key lockout.

The Apple Extended Keyboard, Extended Keyboard II, and Apple USB keyboards do not have the two-key lockout. If you are using an application that requires you to hold down multiple keys, you can use one of these keyboards.