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Windows 2000 Performance Guide by Odysseas Pentakalos, Mark Friedman

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Page Replacement

Before we delve into the available Windows 2000 memory and paging measurements, it is important to understand the page replacement policy Windows 2000 uses. Following a policy of allocating real memory page slots on demand as they are referenced inevitably fills up all available physical memory. A common problem virtual memory operating systems face is what to do when a page fault occurs, a valid page must be retrieved from the paging file, and there is little or no room left in physical memory for the referenced page. When real memory is fully allocated and a new page is referenced, something has to give. A page replacement policy decides what to do when this happens.

Available Bytes

You can watch real memory filling up in Windows 2000 by monitoring Available Bytes, which represents free, unallocated RAM. Available Bytes counts the number of free pages in RAM at any particular time; it is the all-important buffer of free pages the OS maintains in order to resolve page faults quickly. The Available Bytes counter, like all the real memory allocation counters in Windows 2000, reports the amount of RAM currently not allocated to any process in bytes. The use of bytes is a legacy from earlier versions of Windows NT, when both 4K Intel pages and 8K Digital Alpha pages were supported. Since you might not necessarily know whether the measurements came from an Intel or an Alpha processor, Microsoft decided to report the data in bytes rather than pages. If you monitor ...

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