That means that the behavior of the operating system is predictable, and can be calculated given a certain load. This has implications for allelements of the operating system. In the RTOS, the relative priorities of tasks are strictly enforced. When a higher priority task is ready to run, it is guaranteed to be run within a deterministic amount of time. Under SVR3, priorities of processes fluctuate depending on their activities.
Memory is allocated from several pools of fixed-sized memory blocks.
The size of blocks varies along pools. This allows applications to allocate and release memory blocks in random order, and be guaranteed that memory remains available in consistent amounts as time progreses. Under SVR3, memory is allocated from heaps. Interrupt entry and exit code is also minimized and deterministic. Under SVR3, process scheduling is suspended during system calls until call completes.