NetWare Peripheral Architecture

Abbreviated NPA or NWPA. A feature of NetWare that allows developers to add and support new storage devices and their associated controllers. NPA consists of the following components:

Host Adapter Module (HAM) The adapter-specific driver that controls the interaction between the operating system and the hardware; provided by Novell or by the manufacturer of the adapter, with the filename extension .HAM. There will be one HAM for each adapter on the server.
Host Adapter Interface (HAI) An API within NPA for communication between the HAM and the NetWare database that tracks the storage devices and media available on the server.
Custom Device Module (CDM) The software that controls the devices attached to the adapter, usually provided by the manufacturer, with the filename extension .CDM. There may be multiple CDMs for a single adapter as each device connected to the adapter needs its own CDM.
Custom Device Interface (CDI) An API within NPA for communication between the CDM and the NetWare database that tracks the storage devices and media available on the server.

The NPA replaces many of the functions found in the NetWare Loadable Module drivers used to control hard disks; the .DSK drivers controlled the hard-disk controller and all the devices attached to that controller.