Multiprogramming with Fixed Partitions (see the Fig. 4.4)

• Except on simple embedded systems, monoprogramming is hardly used any more
• A simple method to accommodate several programs in memory at the same time (to support multiprogramming) is partitioning
• The easiest way to achieve multiprogramming is simply to divide memory up into n (possibly unequal) partitions during system generation or startup
• When a job arrives, it can be put into the input queue for the smallest partition large enough to hold it
• The aim of multiprogramming is to increase the CPU utilization
• $CPU utilization=1-p^n$, where n is the number of processes in the memory, p is waiting-time fraction that a process spends for I/O.
• say $p=0.8$, means process spend 80 percent of their time waiting for I/O and n=10; then $CPU utilization=89\%$, in other words CPU wasted 11 percent.

Figure 4.4: (a) Fixed memory partitions with separate input queues for each partition. (b) Fixed memory partitions with a single input queues.