Special Features on Windows 
The Windows NT file cache directly competes with SAP R/3 programs and pushes these programs out of the working memory. Unlike UNIX, the file cache is only influenced indirectly by a switch in the network setting.
Writing and reading SAP R/3 roll and paging blocks in the relevant storage files extends the Windows file cache and pushes out the SAP R/3 programs from the working 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 address area of an active process are transferred automatically in the page file by the operating system. The pages remain duplicated in the physical memory until the memory area 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 lazy page out, the memory area is included again without the page file access. If there is enough working 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 working 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