/PAE for use of 4GB of RAM with Windows XP x32

Started Sep 28, 2007 | Discussions thread
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Yyrkoon Senior Member • Posts: 1,076
/PAE for use of 4GB of RAM with Windows XP x32

I would like to start off in saying that there seeems to be a lot of confusion on these forums concerning 32bit Windows, and 4GB of ram. Some seem to think the only way to do this is by using the 3GB boot.ini option, but this is not nessisarily the case.

Also, there seems to be confusion as to whether Windows XP will actually use all 4GB if installed or not. The simple answer to this question is yes, windows will use all of your 4GB of RAM, but depending on your system configuration, and boot.ini options, the actual memory availible for running programs may vary from 2.5GB-3.5GB, possibly slightly more with what is reffered to as 'memory hoisting'.

1). Having 3.5GB of memory availible does not mean that a single application can address, or use that amount of RAM. The default settings in Windows allows for a single process, or application to adress up to 2GB at a time. However, some applications that are multithreaded, or run multiple processes at once for different aspect of the main program, may be able to work arround this issue by allocating up to 2GB of RAM for each dedicated process.

2). If you have 4GB installed, or are considering using 4GB on a x32 version of Windows, you will gain an advantage if not a noticable performance gain while running single, or multiple programs at once. For instance, a machine with 2GB of RAM installed, all you are running is Photoshop, and if you allow Photoshop to use 100% of the installed RAM availible, Windows may be starved for memory, only having 300MB-500MB for its own personal use, and other applications you may be running. Depending on your Video sub system, this can also slow your graphics performance slightly, as some of this memory set aside for the Opterating system is used for your Video cards memory aperature. As an example, I have 4GB of memory installed in my current system, 3.5GB is availible for applications, when using some tools such as the smudge tool, with the rough round bristle brush , I can use this tool at a much larger size now without experiencing screen 'lag' comparred to when I had only 2GB installed. Hence, I notice a real world performance gain right from the start.

3) the PAE boot option while not letting you allocate all memory up to 3GB for a single application(virtual memory), it can reclaim some of that last 1.5GB of RAM you may/may not be able to use for applications without it. This has largely to do with your system configuration, and how many devices require memory set aside for them, such as your Video card. If your Video card only has a reasonable amount of RAM on it(say 256MB), the chances of you having the ability of using 3.5GB of the 4GB installed is highly likely(so long as you do not have tons of other descrete cards, or hardware reserving memory space).

So far, I have personally experienced a very stable system using the PAE boot.ini option. While I cannot use all of the availible RAM for a single application, I have found my computing experience to be much smoother so far. Applications start quicker, applications close quicker, and in general running multiple applications at once no longer seems to drag my system down like it once did when using only 2GB of RAM. Does it make a huge difference ? In general no, it does not, but the difference is noticable, especially when using Photoshop on large images with a 16BIT color depth, and performing various operations.

Everything I have mentioned here applies to Windows XP, and may be different dpending on the different versoin of Windows(Windows 2003 for example).

For the technicalities PAE, you can visit: http://en.wikipedia.org/wiki/Physical_Address_Extension

And do not forget to visit the MSDN/Microsoft links at the bottom for futher information on PAE, 3GB, 4GT, DEP, AWE, and NUMA technologies/Boot options.

For thsoe of your interrested in my system specifications, I use:

An AMD AM2 1210 Opteron overclocked to 2.25Ghz(1.8 Ghz stock), 4x 1GB of Corsair 6400 XMS2 memory(V5.1 ProMos), a 256MB eVGA 7600GT, an Intel Pro PT 1000 GbE PCIe NIC, on an ABIT NF-M2 nView motherboard. 7x various Seagate HDDs for 2.1 TB of total storage(probably not related . . .).

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