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SVR5, like SCO SVR5 2.0 and SCO OpenServer 5 is a multiprocessing operating system that uses multiple CPUs to execute more than one process simultaneously, thereby increasing overall system performance.
The multiprocessor extension for the SCO OpenServer 5 Release 5 system is called SCO Symmetrical Multiprocessing Support, which is activated by the SCO SMP License. The multiprocessor extension for earlier releases of SCO systems was called the SCO® MPX® system.
For optimal performance, drivers should be multithreaded when running on multiprocessing configurations; this means using synchronization variables rather than sleep(D3) and wakeup(D3) to synchronize the driver with the hardware and using the various locks rather than spl(D3) to protect critical code sections. Single-threaded drivers can be run on multiprocessor configurations without being modified; they will always run on the default CPU and may not perform as well as multithreaded drivers.