Using Memory Beyond 4GB in SQL Server

Physical Address Extension (PAE) allows you to use up to 64 GB of physical memory depending on operating system you use. All existing 32 bit processors supports this extension of memory. PAE mode requires an Intel Architecture processor and more than 4GB of RAM.

You can configure at two levels to use Memory Beyond 4GB in a 32 bit windows server operating system.

1. Operating System Level
2. Application Level

To enable operating system to access more than 4GB of physical memory , add a /PAE switch in boot.ini file as below

[boot loader]

timeout=30

default=multi(0)disk(0)partition(1) \WINNT

[operating systems]

multi(0)risk(0)rdisk(0)partition(1) \WINNT=”Microsoft Windows Server 2008 Advanced Server ” /fastdetect /PAE

once you modified the boot.ini file, use sp_configure to enable SQL Server 2008 to use more than 4GB of physical memory

   1: sp_cofigure 'show advanced options', 1

   2: RECONFIGURE

   3: GO

   4: sp_configure 'awe enabled', 1

   5: RECONFIGURE

   6: GO

   7: sp_configure 'max server memory', 5120

   8: RECONFIGURE

   9: GO

  10:  

In order to effect your changes restart your operating system and SQL Server.

max server memory parameter is mandatory while using AWE memory. The above example tells how to enable 5GB memory.

NOTE if you use the /3GB feature with AWE/PAE , then SQL Server is limited to a maximum of 16GB of extended memory. Therefore you should bot use /3GB switch to access memory beyond 16GB

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