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Does AWE help on a 64-bit server? The option is still available. Does it do anything?

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4 Answers 4

AWE is similar to the old banked switched EMS that we used to have in the 286 and 386 days. It allows access to a large (> 4Gb) address space, by bank switching it through a small (256mb ?) window at the top of the 32bit process address space.

Certain applications, like SQLServer, can take advantage of this memory for storing semi structured data, like the database page cache. AWE memory cannot be used to allow your 32bit program to address more than the standard 3Gb address space.

In short, if you have a 64bit OS, don't use AWE, you don't need it.

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AWE is irrelevent on a 64 bit O/S as it can support a large contiguous in core image. The facility is a hack based on a facility in the Xeon and other 32-bit CPUs called PAE (Physical address extensions) that allows the MMU to support a 36 bit wide physical address bus. The wider address bus allows a machine with this facility to address 64GB of physical RAM, although a single process can still only see 4GB at a time.

AWE is a trick that uses an API provided by windows that allows a process to manage the MMU. Using this API the process can reserve a pool of physical memory and swap chunks of it in and out of areas in its virtual address space. This Stackoverflow posting discusses the mechanics of it in more detail with some links to external resources.

The virtual address space of a process on a 64 bit server is much wider so you do not have to use this type of facility to address more than 4GB of physical RAM. A process can natively work with 2**64 (roughly 1.8E19) distinct addresses (i.e. pointers are 64 bits wide).

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Not that I've ever seen. SQL can use all available memory on a 64-bit system. AWE's purpose is to do the same for 32-bit.

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The other answer explain in detail why - but to summarize - The AWE option on 64 bit servers does not do anything and is not required

Quote

AWE is not required and cannot be configured on 64-bit operating systems.

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