Operating System Memory Virtual Memory - Swap Files

Virtual memory provides applications with more RAM space than allocated in the computer. A technique which operating systems use to load more data into RAM than it can hold. Part of the data is kept on disk and is constantly swapped back and forth into system memory. For instance, when your run a CD application.      Whenever the operating system needs a part of memory that is currently not in physical memory, a VIRTUAL MEMORY MANAGER picks a part of physical RAM that hasn´t been used recently, writes it to a SWAP FILE on the hard disk and then reads the part of RAM that is needed from the swap file and stores it into real RAM in place of the old block. This is called SWAPPING. The blocks of RAM that are swapped around are called PAGES.      Virtual memory allows for the multitasking (opening more than one program) that we do.      When the amount of virtual memory in use greatly exceeds the amount of real memory, the operating system spends a lot of time swapping pages of RAM around, which greatly hampers performance. This called THRASHING and you can see it in your LED hard disk drive light. The hard disk is thousands of times slower than the system RAM, if not more. A system that is thrashing can be perceived as either a very slow system or one that has come to a halt. Hard disk access time is measured in thousandths of a second; RAM access time is measured in billionths of a second.

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Last Update: 10:36 PM 6/29/01