· The Windows file cache directly competes with SAP programs and pushes these programs out of the physical memory. Unlike UNIX, the file cache is only influenced indirectly by a switch in the network setting.
· Writing and reading SAP roll and paging blocks in the relevant storage files extends the Windows file cache and pushes out the SAP programs from the physical memory.
· Copying roll and paging blocks when changing contexts is more time-consuming than including memory blocks when using Extended Memory. Extended Memory also has the advantage that it is subject to the performance-oriented Windows paging mechanism.
· Pages in the extended memory that are not in the working set of an active process are transferred automatically in the page file by the operating system. The pages remain in the physical memory until the space is required by another process. They are marked as transferred. The transfer has a low priority and is described as a lazy page out. If a work process now accesses a transferred page, it is used again without access to the page file. If there is enough physical memory, the result is a large [page out] and a small [page in] value. When a lazy page out action occurs, Windows creates permanently free available physical memory. Therefore, even a page-in with a page file access is faster than on UNIX systems, since it is not necessary to transfer another page beforehand (no direct page-out before a page-in).
See also: SAP Extended Memory