What IS the maximum amount of RAM Win XP can address?

Torn · 18th May 2007, 10:41 PM

I see on some builds where people are planning to put 4 Gb of RAM on machines running Win XP.

I thought 3 Gb was the maximum practical for Win XP.

Am I wrong?

nux · 18th May 2007, 10:48 PM

It will work, just wont use it effectively. Using the /3GB switch helps.

maxy0987 · 18th May 2007, 10:52 PM

People building with 4gb are probably thinking about what happens when they move to vista.

I know Vista was the reason i got 4gb, im still running XP atm but that's only short term

oli · 18th May 2007, 11:19 PM

Apparently it depends on a number of things, including the amount of memory your video card has.

I've done a bit of reading into it and it seems Windows XP can address more than 3GB, but never the total 4GB. No single application can be allocated more than 2GB either.

Chemware · 19th May 2007, 10:52 AM

This is complex.

WinXP can address 4G RAM, but the upper 400-700M is occupied by devices such as video cards, network cards, etc. So Windows (and sometimes motherboards) will report a value like 3,375 MB when 4G is installed.

Standard WinXP allocates 2G of virtual memory to each process, but when PAE is enabled with the /3G boot option, each process that is marked as PAE compatible is allocated 3G. Note that the process binary must be compiled with a PAE-aware memory manager, otherwise Bad Things (TM) happen. PAE /3G mode can therefore be less stable if a there is a driver that does not use a PAE-aware memory manager.

Win64 (Vista64) always boots in PAE mode.

Torn · 19th May 2007, 1:30 PM

Quote:

Originally Posted by Chemware

This is complex.

...when PAE is enabled with the /3G boot option....

Just 3 quick questions...

What is PAE?

What is a /3G boot option?

How are they enabled?

nux · 19th May 2007, 1:32 PM

Quote:

Originally Posted by Torn

Just 3 quick questions...

What is PAE?

What is a /3G boot option?

How are they enabled?

http://www.google.com.au/search?clie...utf-8&oe=utf-8

http://www.google.com.au/search?hl=e...G=Search&meta=

Torn · 21st May 2007, 9:48 AM

Quote:

Originally Posted by nuxie1

http://www.google.com.au/search?clie...utf-8&oe=utf-8

http://www.google.com.au/search?hl=e...G=Search&meta=

Thanks for that.

18th May 2007, 10:41 PM	#1
Torn Member Join Date: May 2007 Posts: 8	What IS the maximum amount of RAM Win XP can address? I see on some builds where people are planning to put 4 Gb of RAM on machines running Win XP. I thought 3 Gb was the maximum practical for Win XP. Am I wrong?

18th May 2007, 10:52 PM	#3
maxy0987 Member Join Date: Jul 2002 Location: Melbourne Posts: 2,337	People building with 4gb are probably thinking about what happens when they move to vista. I know Vista was the reason i got 4gb, im still running XP atm but that's only short term __________________ 8800GTX @ 621/1008 - E6600 @ 3Ghz - 4GB Kingston DDR2 all on a P5W-DH-Deluxe 27/06/2006 - The socceroos were eliminated from the world cup due to a poor ref decision. Never forget, support the 'roos in their quest for the next world cup.

19th May 2007, 10:52 AM	#5
Chemware Member Join Date: Nov 2005 Location: Melbourne Posts: 250	This is complex. WinXP can address 4G RAM, but the upper 400-700M is occupied by devices such as video cards, network cards, etc. So Windows (and sometimes motherboards) will report a value like 3,375 MB when 4G is installed. Standard WinXP allocates 2G of *virtual memory* to each process, but when PAE is enabled with the /3G boot option, each process that is marked as PAE compatible is allocated 3G. Note that the process binary must be compiled with a PAE-aware memory manager, otherwise Bad Things (TM) happen. PAE /3G mode can therefore be less stable if a there is a driver that does not use a PAE-aware memory manager. Win64 (Vista64) always boots in PAE mode. __________________ Successful trades with bevros, Burnzy, jET_M@X, Ken_H, v81, Tasty_Vito, shaneric, cittris, Riquez83, mobius.ro, joe_lam65, /\/\usE+, mute, crag_v Precision M4700, i7-3720QM, Firepro 4000M, Momentus XT 500G + 500G, 8GB ram; AMD X4 955 @3.8, 2T WD, 2x2G G.Skill 1600, Radeon 6870

18th May 2007, 10:48 PM	#2
nux Member Join Date: Jan 2002 Location: Melbourne Posts: 16,790	It will work, just wont use it effectively. Using the /3GB switch helps.

18th May 2007, 11:19 PM	#4
oli Member Join Date: Jun 2002 Location: The Internet Posts: 7,178	Apparently it depends on a number of things, including the amount of memory your video card has. I've done a bit of reading into it and it seems Windows XP can address more than 3GB, but never the total 4GB. No single application can be allocated more than 2GB either.