Information Technology Reference
In-Depth Information
the computer. Because the processing of programs may access this
material frequently, virtual memory usually is placed on a disk with
relatively fast access times, such as a hard disk, rather than a rela
tively slow floppy disk or removable disk.
With this virtual memory, pieces in actual use (called
pages
) are
loaded into main memory, just as the most recently used program
instructions and data from main memory are loaded into cache and
retrieved. During execution, moderatesized pieces of the applica
tion first move from virtual memory (on a disk) to main memory,
and then smaller pieces move to cache and the CPU as needed.
When program execution moves from one part of the program or
one part of data to another, the pieces in main memory and cache
can be updated appropriately. Schematically, this organization of
memory is shown in Figure 3.3.
Virtual Memory
on disk divided
into pages
Main Memory
with pages and
lines
Cache Memory
with lines
Figure 3.3
Levels of computer memory.
