The memory of a system is almost constantly filled to capacity. Even if currently running programs do not consume all available memory, the operating system retains in memory the text pages of programs that ran earlier and the files that they used. There is no cost associated with this retention, because the memory would have been unused anyway. In many cases, the programs or files will be used again, which reduces disk I/O.
This chapter describes how memory use can be measured and modified. It contains the following major sections:
Readers who are not familiar with the operating system's virtual-memory management may want to look at Performance Overview of the Virtual Memory Manager (VMM) before continuing.