4.2. Memory and Address Protection
The most obvious problem of multiprogramming is preventing one program from affecting the memory of other programs. Fortunately, protection can be built into the hardware mechanisms that control efficient use of memory, so that solid protection can be provided at essentially no additional cost.
Fence
The simplest form of memory protection was introduced in single-user operating systems, to prevent a faulty user program from destroying part of the resident portion of the operating system. As its name implies, a fence is a method to confine users to one side of a boundary.
In one implementation, the fence was a predefined memory address, enabling the operating system to reside on one side and the user to stay ...
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