You can enable the lock pages in memory permissions to prevent SQL Server 2005 64-bit buffer pool memory from being paged out of physical memory

Under certain circumstances, the working set of the Microsoft SQL Server 2005 64-bit process may be paged out by Microsoft Windows. This behavior may cause a decrease in SQL Server 64-bit performance. Microsoft has found an issue that may cause the SQL Server 2005 64-bit working set to be trimmed.

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