All storage devices require drivers. The NetWare Peripheral Storage Architecture (NWPA) divides device drivers into two kinds: a custom device module (CDM) that drives the device itself and a host adapter module (HAM) that drives the adapter to which the device is attached.
CDMs drive storage devices, including autochangers, that are attached to the host adapter bus.
CDMs are device-specific. For example, if there are three different types of storage devices attached to the host adapter (such as a CD-ROM drive, a SCSI hard drive, and an autochanger) then a specific CDM for each type of device must be installed.
A HAM is the driver component associated with the host adapter hardware. HAMs provide the functionality to route requests to the bus where a specified device is attached.
HAMs are adapter-specific. For example, if a third-party adapter is installed in the server, a HAM developed specifically for that adapter must be installed.
Loading HAMs and CDMs is much like loading other device drivers, but instead of loading one .dsk file for both the adapter and device, you load one .ham file for the adapter and one .cdm file for each type of device attached to the adapter.
When you want to connect a new hardware device to the host bus adapter, you need to load only the appropriate CDM for that hardware device (in addition to the HAMs and CDMs already loaded, and assuming a compatible adapter is installed).