The Apple Desktop Bus (ADB) chip controls interactions between the processor and input devices. Up to 16 input devices, such as keyboards, a mouse, digitizing pads, trackballs and bar-code readers, can be connected to the computer and used at one time.
The actual number of devices that can connect to the ADB depend on the power needs of the individual devices. For example, keyboards draw a comparatively large amount of power; only four or five keyboards or similar devices could be connected at once. However, if some devices include their own power supply, the device limit could be higher.