Page 158 - DCAP103_Principle of operating system

Unit 5: Memory Management

Notes
Figure 5.2: Dynamic Relocation using a Relocation Register

Relocation
registor
14000
Logical Physical
address address
CPU Memory
346 14346

MMU

5.3 Swapping

A process needs to be in memory to be executed. A process, however, can be swapped
temporarily out of memory to a backing store, and then brought back into memory for
continued execution. For example, assume a multiprogramming environment with a round-
robin CPU-scheduling algorithm. When a quantum expires, the memory manager will start
to swap out the process that just finished, and to swap in another process to the memory
space that has been freed (Figure 5.3). In the meantime, the CPU scheduler will allocate a
time slice to some other process in memory. When each process finishes its quantum, it will
be swapped with another process. Ideally, the memory manager can swap processes fast
enough that some processes will be in memory, ready to execute, when the CPU scheduler
wants to reschedule the CPU. The quantum must also be sufficiently large that reasonable
amounts of computing are done between swaps.

Figure 5.3: Swapping of Two Processes using a Disk as a Backing Store

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