Legacy Macintosh devices are connected via the Apple Desktop Bus (ADB). This is a simple serial bus that can connect multiple devices. Protocols for devices (such as keyboard, mouse) are specified, too.

The ADB controller in the Macs is called CUDA. It is implemented by a Motorola MC6800 micro-controller, which probably is not important from a device-driver point of view. The chip which connects the Mac's I/O space to the CUDA is a ​MOS Technology 6522, also called VIA (Versatille Interface Adapter).