Background

Preceding sections talked about how to avoid memory fragmentation by breaking process memory requirements down into smaller bites ( pages ), and storing the pages non-contiguously in memory. However the entire process still had to be stored in memory somewhere.

In practice, most real processes do not need all their pages, or at least not all at once, for several reasons:

1. Error handling code is not needed unless that specific error occurs, some of which are quite rare.
2. Arrays are often over-sized for worst-case scenarios, and only a small fraction of the arrays are actually used in practice.
3. Certain features of certain programs are rarely used, such as the routine to balance the federal budget.

The ability to load only the portions of processes that were actually needed ( and only when they were needed ) has several benefits:

• Programs could be written for a much larger address space ( virtual memory space ) than physically exists on the computer.
• Because each process is only using a fraction of their total address space, there is more memory left for other programs, improving CPU utilization and system throughput.
• Less I/O is needed for swapping processes in and out of RAM, speeding things up.