A number of devices connect to the N64. This tutorial explains how to use those devices that connect via the SI (Serial Interface) and via the PI (Parallel Interface).

Devices that connect via the SI include the Standard Controller and the Controller Pak. Devices that connect via the PI include SRAM and the 64DD.

The explanations in this tutorial concern use of the device functions of the NuSystem system library. If you use NuSystem, there is virtually no need to make direct use of the N64OS device functions.