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The ability of Mac OS to support generic native drivers does not mean that Mac OS contains a fully native I/O subsystem; at present the Device Manager still runs in 68K code. In addition, the 68K emulator can service interrupts only on 68K instruction boundaries. As a result, the performance of a native device driver may be greater or less than the performance of its 68K equivalent. At this time, Apple has made no commitment to furnish either a native version of the Device Manager or a combined native-68K version (fat version).
The discussions of generic native drivers in the previous sections apply only to drivers managed by the Device Manager. Other driver-like things, such as Apple Desktop Bus drivers, which are not managed by the Device Manager, realize no benefit from the Device Manager's concurrency features. These features are discussed in the next section.