• A 32 bit OS can only use 4GB of memory total, that means if you have 4GB of ram and your graphic card has 1GB of ram, you have a total of 5GB of memory.

• Out of that 5GB of memory, you can only use 4GB total. 1GB the graphic card will take up, so now the 32bit OS can only use 3GB. 

• Enabling PAE, will limit to the OS to 2GB total. What PAE does is dedicate 2GB to OS and the other 2GB to anything other then the OS. Apparently some people don't understand how PAE works and think that some how it can magically make a 32bit XP use more then 4GB, which is impossible, so after noticing my explanation is not getting through, I thought a visual from MS itself might help sink it in, you can see it here: http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx     
  • The 'fact' above is the perfect example of this misunderstanding. PAE has nothing to do with the user and kernel pool being seperated.
  • Many confuse virtual memory with physical memory. All requests for memory by applications; that is running processes, such as explorer.exe, wmplayer.exe, dwm.exe, iexplore.exe, etc; are furfilled using virtual memory. Virtual memory is just an abstraction which includes physical memory and your pagefile(s). Yes, virtual memory includes physical memory!

• Vista 32bit can see only 3.5GB of ram total. The new sp1 only reports how much memory you have intalled, not how much memory you can use.

"Apparently some people don't understand how PAE works and think that some how it can magically make a 32bit XP use more then 4GB, which is impossible, so after noticing my explanation is not getting through, I thought a visual from MS itself might help sink it in, you can see it here: http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx"


I also mistakenly thought a 32bit operating system could only use 4GB, having only 32 address bits to work with. But as you can see from the tables above, 32bit Windows Server 2008 can use up to 64GB of physical memory. Turning on the PAE feature modifies the virtual address mapping used by the processor hardware. There is a good explanation on Wikipedia:
http://en.wikipedia.org/wiki/Physical_Address_Extension

Very basically, each process is still limited to 4GB because of the 32bit addresses, but the OS can use a processor control register to map that 4GB space above the 4GB. So process "A" might have it's 4GB virtual address space start in physical ram at 8GB, process "B" at 12GB, etc.

Many people will doubt this because of their personal experience with Microsoft 32bit desktop operating systems. Microsoft has specifically limited the desktops to 4GB for driver compatibility reasons.

Correction, read my facts again and you will see I specifically said "XP 32 bit", second I point to ms's own site and you take us to wiki which anybody can edit? since when is wiki's info more reliable then ms's own site when we discussing ms's OS? lol

In short XP 32-bit can't see more then 4GB of ram total no matter what you do, and its clearly stated here by MS:http://www.microsoft.com/whdc/system/platform/server/PAE/PAEdrv.mspx

yes other 32-bit OS-es can use more then 4GB of ram but not XP 32-bit

"I running windwos Vista 64-bit with 8-GB of ram. Most of my applications are 32-bit applications. How much RAM can VISTA dedicates to 32-bit application?"

64 bit editions of Windows can only attribute a total of 4 GiB of RAM to any single 32 bit virtual memory instance (or application), regardless of your total RAM. The reason is simple, 64 bit editions of Desktop Windows run on the x86-64 architecture, which is a processor architecture capable of running both 64 and 32 bit instructions, limiting 32 bit instructions (or applications) to what 32 bit limits them to, thus, 4 GiB of RAM.

Intel and AMD's specification of PAE does support the x86-64 architecture but the software layer of Microsoft's PAE (the API), called AWE, is not supported on 64 bit editions of Windows, so Windows Vista 64 bit cannot attribute more than 4 GiB of RAM for a 32 bit application.

In fact, true 64 bit architectures like the Intel Itanium processor do not support 32 bit applications. The only reason 32 bit applications work on 64 bit editions of desktop Windows is because the very architecture at its core, called x86-64 (often erroneously shortened to x64), is a hybrid architecture capable of running both 32 bit and 64 bit instructions.

It's also the reason why drivers may not work in 32 bit, but applications will, on Windows Vista 64 bit. The Windows Vista 64 bit kernel is written in 64 bit, and thus, drivers must also be written in 64 bit. If Microsoft would have made the kernel in 32 bit, expanded support would have had to rely on PAE, but drivers wouldn't have had to be re-written. In fact, Apple used that strategy with Mac OS X's transition to 64 bit processors and only its future Snow Leopard will have its kernel in 64 bit.



"I also mistakenly thought a 32bit operating system could only use 4GB, having only 32 address bits to work with. But as you can see from the tables above, 32bit Windows Server 2008 can use up to 64GB of physical memory."

Note however that Windows Server 2008 32 bit uses PAE to achieve this.



"The limit for 64-bit XP is given as 128 GB, while on the support site, http://support.microsoft.com/kb/283247/en-us, it is given as 16 GB!
What is correct, 16 GB or 128 GB?"

Short answer is 128 GiB of RAM.
While Windows XP Pro 64 bit can theoretically support 128 GiB of RAM, driver issues, lack of motherboard support and PAE's Intel technical spec limit to 64 GiB can limit this. Very few 32 bit systems will be built to handle 128 GiB of RAM as the use of a 64 bit operating system becomes much more advantageous in this situation.


I have an article on my blog, Pacoup.com, but you'll have to find it yourself as I cannot link to my own articles on MSDN.

WROTE:

XP and Vista can only truly manage ~3GB of Physical RAM. 4GB is misleading.

Quote:

Xp and Vista can truly manage ~4GB of physical RAM, but shows only the "available" ram. If you have a onboard vídeo with 512mb and something else on-board to complete 1gb, your manager will show only 3GB "available".

QUOTE: PP

Xp and Vista can truly manage ~4GB of physical RAM

The limit for 64-bit XP is given as 128 GB, while on the support site, http://support.microsoft.com/kb/283247/en-us, it is given as 16 GB!

What is correct, 16 GB or 128 GB?

Some customers have been reported problems with running 64-bit XP on 32 GB RAM. Can you clarify if 32 Gb RAM is supported and if so, what was the purpose of information in KB 283247

There was a Windows 2003 x64 verison i.e. NON R2 so why does it list this as Not applicable ? Should be 32gb for x64 same as R2 version?