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What is Address Windowing Extensions (AWE)

  • Nov 04 / 2008
  • 0
dbDigger, Performance Tunning and Optimization, System Administration

What is Address Windowing Extensions (AWE)

Address Windowing Extensions (AWE) is a set of extensions that allows an application to quickly manipulate physical memory greater than 4GB. The process of mapping an application’s virtual address space to physical memory under Address Windowing Extensions (AWE) is known as “windowing,” and is similar to the “overlay” concept of other environments. Certain data-intensive applications, such as database management systems and scientific and engineering software, need access to very large caches of data. Using the Address Windowing Extensions (AWE) API, the application can map the virtual window to any one of the physical regions. The application can reserve more than one virtual address space and map it to any of the allocated regions of physical memory, as long as the number of bytes reserved in the virtual address space matches that of the physical memory region. Address Windowing Extensions (AWE) usage is coded into the application itself. An application must have the Lock Pages in Memory privilege to use Address Windowing Extensions (AWE). To use AWE, you must enable the physical address extensions by adding the /PAE switch to your boot.ini file. Starting with Windows 2003 SP1, Windows automatically enables PAE on boot when more than 2 GB of RAM is installed. Some major benefits of AWE are:

  • A small group of new functions is defined to manipulate AWE memory.
  • AWE provides a very fast remapping capability. Remapping is done by manipulating virtual memory tables, not by moving data in physical memory.
  • AWE provides page size granularity appropriate to the processor (for example, 4K on x86), which is more useful to applications than large pages (for example, 2MB or 4MB on x86).
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