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The UnixWare operating system uses virtual address space for all user processes and for the kernel. Because two or more processes can share memory by mapping a portion of their virtual address space to the same physical memory, the memory management subsystem controls the contents of physical memory and maintains the data tables used by the hardware to translate from virtual to physical addresses.
By keeping control of memory, the memory management subsystem keeps processes separate in address space. By keeping track of the location of processes in memory, keeping processes separate in memory, keeping memory and the data tables that point to memory updated, maintaining the integrity of memory and data tables, and zeroing out or properly reinitializing memory before reuse (see ``How object reuse relates to security''), the memory management subsystem enforces security.