Windows 2GB Memory Allocation Limit

[Neo_Geo]

I have heard that a 32bit OS should theoretically be able to address 4GB or memory... But for reasons unknown to me WinNT (and thus Win2k and XP) can only address about 2GB.

Is this true???

The reason I am asking is that I know of someone who has 1.5GB of RAM installed and a 4GB pagefile. He is using some pretty high end CAD software and having problems with system stability. I suspect that his large amount of memory allocation could be part of his problem.

Thanks

 

[AndyHui]

No, it's not true.

Please read the FAQ: What is the maximum amount of RAM for Windows?

 

[Neo_Geo]

Thanks for the clarification,

One more question:
Is the sum of RAM and Virtual Memory (pagefile) limited to 4GB? Or does the 4GB limit only apply to RAM, with additional memory available through virtual memory?

 

[AndyHui]

The sum of the page file and physical memory should not exceed 4GB.

 

[GlassGhost]

Actually, to be "highly technical", LOL, Windows NT4 is able to use Intel's 36-bit extensions which allow for 2^36 or 64 GB of memory to be directly addressable. http://www.intel.com/support/processors/pentiumII/xeon/intro.htm

 

[Neo_Geo]

Hmmm that is interesting....
More questions:
Does this 64GB limit only apply to "Xeon" processors?
Is only NT4 able to take advantage of the 36bit extensions?
What about Win2kPro, WinXP Home, WinXP Pro???

Thanks a bunch, amazing what someone can learn at the Anandtech forums!
This subject could make a great FAQ... Hint Hint Hint

 

[GlassGhost]

Its 64GB, *not* 8GB. I know that NT4 has support, I'm guessing Win2k and XP do as well, but I'm not too sure. The 36-bit extensions are on the die of all processors after the P-Pro I think, but like hyperthreading, I think Intel didn't enable them except on PII & PIII Xeon processors. I don't think its on the P4 Xeon b/c of IA64, i.e. the Itanium.

To be honest, I don't feel like doing all the research to back up my guesses 🙂

 

[AndyHui]

The Page Size Extension 36 Flag on Intel processors present on the P6 core (although it was only activated from the Deschutes processor onwards) allows memory addressability up to 64GB.

Special OEM versions of Windows NT (such as WinNT Enterprise Server), Windows 2000 Advanced Server and Windows 2000 Data Center, can take advantage of PSE36.

PSE36 is NOT supported by Windows 2000 Professional, Windows 2000 Server, Windows XP Home and Windows XP Professional.

Using PSE36 does incur a hit to performance, and regular users are not expected to need anywhere near 4GB for most uses.

Using PSE36 is not a frequently asked question, nor is it really highly technical. That's up to the mods, I guess.