Increase memory with 'Physical Address Extension'

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Have you ever examined your Windows 2000 Advanced Server machine and wondered why it only reports 3.4 GB of RAM as being installed? Curious, especially since Advanced Server is capable of utilizing up to 8 GB of memory! Check your 'boot.ini' file for the /PAE switch in the ARC path as defined in the 'operating systems' section.

If the entry is not present, follow this procedure to add the switch:

  1. Locate the 'boot.ini' file, typically in the root folder (for example, C:) and remove its read-only attribute.


  2. Open the 'boot.ini' file, and then add the /PAE parameter to the ARC path, as shown here: multi(0)disk(0)rdisk(0)partition(2)WINNT="Windows 2000 Advanced Server" /PAE


  3. On the File menu, click Save.
  4. Restore the read-only attribute to the 'boot.ini' file.
  5. Recycle the server to allow PAE to take effect.

Windows 2000 Physical Address Extension (PAE) enables the operating system to utilize memory beyond normal 32-bit virtual addressing. It also allows the use of greater than 4 GB installed memory by the OS, and any applications written to use the Address Windowing Extensions API set. Even applications not using the AWE API benefit from using now-available

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lower memory space while the Windows operating system utilizes virtual address space mapped to the greater physical memory. Windows normally limits applications up to 2 GB of memory space. With PAE enabled, 3 GB of memory can be allocated to applications, while the last 1 GB of 32-bit memory space is used by the OS.

Virtual memory mapped above 4 GB is available for data caching or paging and reduces the need for disk access by keeping the data in memory. Microsoft recommends enabling PAE for applications that move large amounts of data into memory such as SQL Server. Use of PAE is available on Intel Pentium Pro or greater systems running Windows operating systems capable of using greater than 4 GB of RAM such as Windows 2000 Advanced Server and Datacenter Server.

This was first published in February 2003

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