When you start Windows 2000 Datacenter Server, you may not
observe any memory greater than 16 GB in size even though you have more memory
in the server.
This behavior can occur if Windows 2000 Datacenter Server
has more than 16 GB of physical memory and is restarted with both the /3gb
switches which are set in the Boot.ini file.
This behavior is by design.
When a computer is started with the /3gb
switch, the kernel space is limited to 1 GB of memory and
properly compiled programs are able to allocate up to 3 GB of memory rather
than the 2 GB of memory that can normally be allocated by a program.
When a computer is started with the /pae
switch, the size of the Page Table Entry (PTE) increases from 4
KB to 8 KB. The number of PTEs that are required when you translate memory is
increased as the amount of memory in a computer increases.
When the /3gb
switch is used, the kernel mode space is limited to 1 GB rather
than the usual 2 GB amount. When a computer contains large amounts of memory,
the combination of reduced kernel space, increased PTE size, and increased PTE
utilization can cause a server to be unable to index any additional memory and
can cause the server to stop responding.
When a computer is started and the presence of the /pae
switches are detected, the operating system does not recognize any memory above 16 GB. If you start the computer without the /3gb
switch, the computer is enabled to locate all available memory up to 32 GB. This behavior protects the stability of the operating system from known conditions and the limitations of providing support for large memory configurations on a 32-bit platform.
For additional information, click the article number
below to view the article in the Microsoft Knowledge Base:
Large Memory Support Is Available in Windows 2000
Information About BackOffice Program Support on Windows 2000 Datacenter Server-Based Computers
HOWTO: Map Adapter RAM into Process Address Space
More information is available at the following
Microsoft Web sites:Managing
Windowing Extensions and Microsoft Windows 2000 Datacenter