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FYIs about using more than 2GB of RAM

From time to time I am reading that more people using Windows Servers with more than 2GB of RAM. Here are some FYIs if you are running or thinking of running more than 2GB of RAM in a Windows 2000 or 2003 Server.

1) A 32 bit architecture means 2^32 which mean an address space of 4GB of RAM. Remember in the long, long ago when we hit the 1MB barrier of the 8088 and the 16MB barrier of the 386. We are about to hit the next barrier.

2) By default, Windows partitions the bottom 2GB of virtual address space for programs and the upper 2GB for the OS. Unless you use the /3GB boot switches in the boot.ini, your applications will be limited to 2GB of RAM. The /3GB switch moves partition from 2GB to 3GB giving more memory to applications.

3) If you use the /3GB switch, some applications and drivers may not work. At times programmers do very bad things like leave the first two digits off the year or use the high bit of an address pointer for a flag. If you need this switch to get more memory for SQL, then you should have SQL on its on dedicated server and lab test before you leap.

4) If you have more than 4GB of RAM, you can switch the memory mode with the /PAE boot switch. Physical Address Extensions turn on a special paging mode in the memory registers. Windows can then page the 2GB area across 64GBs of physical memory bank. Applications like SQL 2000 can take advantage of PAE via AWE (Address Windowing Extensions) memory allocations.

5) To use more than 4GB of RAM, you need /PAE in the boot.ini and you must enable AWE in SQL for SQL 2000 to take advantage of all that money you spent.

6) Windows 2000/2003 Server supports 4GB of RAM. If you want to use more than 4GB, you have to move up to Windows 2000 Advance Server which supports 8GBs of RAM or Windows Server 2003 Enterprise Edition which supports 32 GB of RAM, and if you have really deep pockets Windows 2000 Data Center which supports 64GB of RAM

7) SQL Standard Edition only supports to 2GB of RAM, to use more than 2GB of RAM you need SQL Enterprise Edition which supports up 64GB of RAM (via AWE)

8) If you are pushing the boundries of SQL this hard, it may be cheaper to move up to Itanium or Opteron with a true 64bit Windows 2003 OS and 64bit version of SQL.


Inside SQL Server 2000's Memory Management Facilities
msdn.microsoft.com/.../default.asp

HOW TO: Configure memory for more than 2 GB in SQL Server
support.microsoft.com/default.aspx




BK
Nobody Special