Allocation of frames


In this topic, you will learn about, Allocation of frames.

Allocation of frames: there is a question that how do we allocate the fixed amount of free memory among the various processes. The processes may have a requirement of either fixed or variable size frames. In both equal and proportional allocation, of course, the allocation may vary according to the multiprogramming level.

Global Vs Local Allocation: it is an important factor that a frame is allocated to the various process in page replacement, with multiple processes competing for frames, we can classify page replacement algorithm into two broad categories:

  1. Global Replacement: it allows a process to select a replacement frame from the set of all frames even if that frame is currently allocated to some other processes i.e., one process can take a frame from another.
  2. Local replacement: it requires that each process selects from only its own set of allocated frames.

One problem with the global replacement algorithm is that a process cannot control its own page fault rate. The set of pages in memory for a process depends not only on the paging behavior of the process but also on the paging behavior of the other process. Therefore, the same process may perform quite differently.

Under local replacement, the set of pages in memory for a process is affected by the paging behavior of only that process.

Thus, the global replacement algorithm generally results in greater system throughput and is therefore the more commonly used method.

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