OPERATING SYSTEM BASICS:10 VIRTUAL MEMORY

Virtual Memory

The term virtual memory is used to describe memory that isn’t what it appears to be. Virtual memory is actually the disk drive space that is manipulated to seem like RAM. Software creates virtual memory by swapping files between RAM and the disk drive, as shown in the following figure. This memory management technique effectively creates more total memory for the system’s applications. However, since there is a major transfer of information that involves the hard disk drive, an overall reduction in speed is encountered with virtual memory operations.

Virtual Memory Operations

Most operating systems since Windows 3.x, Windows 9x, Windows NT, Windows 2000, UNIX, and LINUX feature virtual memory operations. Within these systems, three types of swap files, temporary, permanent, and variable are used. Some operating systems will permit either a permanent or temporary swap file to be established on the system’s hard drive. A permanent swap file is always present and has a constant size. It is composed of contiguous clusters on the drive and cannot be established in the fragmented drive space. It also cannot be established on a compressed partition. The following list shows the types of swap files supported by various Microsoft operating systems:

·         Temporary swap files: Windows 3.x

·         Permanent swap files: Windows 3.x, NT, 2000

·         Variable swap files: Windows 9x

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