Does anyone knows for certain, can XP 32 bit recognise 4GB of DDR2 RAM??

Yes.

But you won't "see" 4GB of RAM. You'll likely see 2.5 - 3GB. Despite this amount being shown in Windows, it really does recognize all 4GB.

FWIW.. Mine shows 3327mb..

No, XP can only see 3.12MB of memory and you need 64 bit memory hogging vista in order to see the full 4 gig. BTW this is a trick from microsoft..

Or you could search.

(Thanks to Scotteq for saving this answer on a file so others can post it when this qustion is asked at least once a week. To the mods: can we have a sticky about this using Scotteq's file as the main post?)

In 32 bit Windows operating systems, the total addressable space available is 4GB. If you installed total 4GB memory, the system will detect less than 4GB of total memory because of address space allocation for other critical functions, such as:

- System BIOS (including motherboard, add-on cards, etc..)
- Motherboards resources
- Memory mapped I/O
- Configuration for AGP/PCI-Ex/PCI
- Other memory allocations for PCI devices

Different onboard devices and different add-on cards (devices) will result of different total memory size. e.g. more PCI cards installed will require more memory resources, resulting of less memory free for other uses.

This limitation applies to most chipsets & Windows XP/Vista 32-bit version operating systems.

If you install a Windows operating system, if more than 3GB memory is required for your system, then the below conditions should be met:

1. The memory controller which supports memory swap functionality is used. The latest chipsets like Intel 975X, 955X, Nvidia NF4 SLI Intel Edition, Nvidia NF4 SLI X16, AMD K8 and newer architectures can support the memory swap function.

2. Windows XP Pro X64 Ed. (64-bit), Windows Vista 64, or other OS which can address more than 4GB memory.

Funny, I have 64-bit XP and see 4GB. It isn't a trick from M$, 32-bit OS's cannot use all 4GB of memory, its the way they're written. 64-bit OS's can.

You're 3.12MB is an unproven number. First, you mean 3.12GB, second, just because your system might show 3.12GB doesn't mean all systems only show 3.12. There have been reports of seeing as much as 3.5GB or as little as 2.5GB.

As said above, it will vary from machine to machine based on memory reservations for other system peripherals. There is no 'trick' a 32bit OS is only allowed to address 4GB of memory, which includes your regular RAM, video RAM, BIOS, etc. A 64bit OS can address something on the order of several TB of memory (Although I think Vista is capped at 64GB or something like that) If you search around the fourms a bit, i know there are threads that break this down with math and everything, lol.

Just got to thinking, the 'trick' you might be refering to is the fact that 4GB ina 64bit OS isnt really more than the 3.5 to a 32bit. Since the 64bit code takes up more memory, there are no gains in going to 64 w/4GB.

To try and make this very simple, as a lot of folks seem to not understand how this works.
XP 32 can use up to 4 gig of memory, that is total memory in your system, counting everything else that has memory on it, in, or attached to it, not just the RAM you are looking at.

For instance, if you have a video card with 512meg of memory, it's address space be allocated first, leaving only ~3.5 gig of main memory available for Windows to use.

Add a HDD with an 8 meg buffer, there goes another 8 meg, add a sound card with on board memory like 525k, there goes another half a meg.

These systems will have their memory allocated first, what ever is left over up to the 4 gig is what you will have available for XP to use from your main memory, or RAM.

On most commonly configured systems, with a couple of hard drives, a 512 meg video card, sound card card, controller cards, etc. Most people wind up with around 3-3.4 gig of main memory available for XP to use.

The exact same rules apply to Vista 32 bit.
Now MS has issued a patch that will cause Vista, (And I think maybe XP as well) to actually show the total amount of main memory or RAM you have in your system, instead of what is left over after allocating space to all the other components first, that it can actually use. A lot of folks think that after this patch is installed, *Pretso* Windows is now using all 4 gig of the main RAM memory installed.
It is not.
It is a display change only, since a lot of people were thinking that something was wrong when they were installing 4 gig and Windows used to only display 3.2 or whatever.

Heh - My posts being reposted...

As pointed out - 32 bit OS's have a 4GB 'bucket' of addresses. System stuff goes in the bucket first. RAM last. When the bucket's full, whatever didn't make it in is effectually ignored. the exact amount will vary depending on system configuration.

32 bit XP shows what's available. 32 bit Vista *used* to show what's available. But as of SP1, it displays all 4GB. This is a display change only. Checking the system tray will tell you what's actually being used and is available for use. MSFT is rumored to have made the change because of millions and millions and millions of n00bz who don't understand address space limitations were flooding websites and support lines all over the world with questions about why their OS doesn't see..... Or maybe it's a grand conspiracy on Microsoft's part to deceive people into thinking their new OS has some value. Or possibly Microsoft saw the need to further disguise what a horriblly bloated pig their complete and total abortion of an operating system *might* someday rise to become, if it were just given a little further refinement. Or possibly the Memory makers are conspiring with Redmond to force people into buying more RAM, instead of staying with 2GB as God Clearly Intended. Or maybe some of the folks here have even more asinine and/or imaginative explanations about how Bill Gates is screwing the world and taking their beloved XP away from them. It might even be possible I'm taking the piss...

Anyways...

32 bit OS = 4GB of address space. The exception is if you have server versions Windows (NT/2003) and manage to get PAE to work with your collection of Large Address Aware drivers. If you don't already know this, then it is likely that you would be best served by not playing with it.

Regarding Vista x64's limits - IIRC, 32GB for basic, 64 GB for Premium. Business/Ultimate can address 128GB. I believe XPx64 does 128GB, but I have no personal experience with that particular OS. So perhaps someone who does may care to confirm/deny.

Beating a dead Horse to death

First, While BOONALITY should read up before posting hogwash, the 3.12 Available may have been correct BUT for Vista Not XP.

Quote (From Ask Dan and may not be valid after vista patches.)
If you've got 4Gb of RAM, by the way, the Vista installer may not work anyway. You can work around that problem, if you have it, by pulling some of the RAM while you install Vista, then putting it back. Apparently Microsoft limit the maximum available memory in 32-bit Vista to 3120Mb
END QUOTE

There is one question I Have been addressed to my Limited knowlege -
Is there any performance benifits from remapping the MIMO's to RAM!
This memory map has to be available somewhere, ie in Bios, or Extended memory. In the OLD days of dos the added the HiMem (640 K to 1 Meg) to remap video and some I/O's. (I used a program call QEMM to manage this area vs MS Himem. And it did provide a performance boost.

Here are two links that explain this. Where Scotteq and I have based our response on.
http://support.microsoft.com/kb/929605
http://www.dansdata.com/askdan00015.htm

Did nobody find my post to be sarcastic? The OP could have done what he/she should do when looking into something and researched.

A couple of notes.

Not everything in the computer that has a ram chip, takes up space in the cpu's address space. For example, the cache on the harddrive is not part of it.

The "trick" is not a "trick". It has been a part of x86 for many years. Some drivers just don't like addresses larger than 2^32, and because of that, Microsoft doesn't break that barrier in xp and vista.

The 3.12GB limitation which a certain KB mentions, uses that number as an example. Nowhere does it say that this is the actual limit. The address space is still 4GB, so 4GB minus MMIO = available to ram

Yeah, I saved your post about this topic and saved it in a text file. Hey, at least I give you credit for it.