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currently active user process.
In this scheme, the operating system loads a program to be executed from disk into
the user area of the memory and executes it. When the process finishes, the
operating system cleans up the user area of the memory and then loads the next
program to be executed.
Although this memory management scheme is simple and easy to implement, it
does not lead to proper utilization of the available main memory resource. This is
because whatever memory space is not occupied by the currently active user
process remains unusued for the entire duration of the process's execution. Hence
this memory management scheme is now used only on very small or dedicated
Multiprogramming Memory Models
We saw that in a multiprogramming system multiple user processes need to
simultaneously reside in the main memory. The two memory management
schemes used to facilitate this are multiprogramming with fixed number of
memory partitions and multiprogramming with variable number of memory
partitions. They are described below.
Multiprogramming with Fixed Number of Memory Partitions
In this scheme, the user area of the memory is divided into a number of fixed-sized
partitions. The partitions may be of equal or unequal size, but the size, of each
partition is fixed. Figure 14.12 shows a multiprogramming memory model with n
equal-sized partitions. Each partition may contain exactly one process. Thus, the degree of multiprogramming is bounded by the number of partitions. That is, at a
time only n processes can be loaded in the system.
All new jobs are put into an input queue. When a partition is free, the next job
from the input queue is picked up and loaded into the free partition. When a
process terminates, the partition occupied by it becomes free for use by another
process waiting in the input queue. Note that if the system uses unequal-sized
partitions, when a partition becomes free, the process closest to the front of the
input queue that fits in it could b...
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This document was uploaded on 04/07/2014.
- Spring '14