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Native drivers are no longer part of the Toolbox environment. The implication of this change is that while 68K drivers can make PBOpen, PBClose, and PBControl calls, these services are not available to drivers in the native device driver environment. Drivers can make calls to other drivers through the Device Manager. Subsystems designed to communicate in this way must be reimplemented.
In the AppleTalk implementation prior to the introduction of Open Transport, the AppleTalk protocol modules are layered on top of networking device drivers using the Device Manager as the interface mechanism between these cooperating pieces of software. The native AppleTalk implementation uses UNIX ® -standard STREAMs communication mechanisms to stack protocol modules on top of drivers. Network drivers are written to conform with the native device driver model and operate within the Open Transport family of devices. For further information, see Network Drivers