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SCO OpenServer offers a thread-based implementation of Asynchronous I/O that supports all file types, as well as a high performance, kernel-based implementation of Asynchronous I/O that supports only raw slices of hard disks.
POSIX interfaces are implemented and included in a single library, libthread, that provides applications with access to this feature. The Asynchronous I/O routines are included in this library and, therefore, you must link with libthread to use these routines.
Figure 12-1 shows the relationship between the Asynchronous I/O interface functions and the common threads library, the two versions of the UNIX Operating System, the interfaces for all the file types, and the Kernel Implementation used for raw slices of hard disks.
Asynchronous I/O interface functions
The following sections detail the various interfaces.