|If your XP Pro is not the 64bit version, you can't actually use all of the 4gb, or all of any amount greater, in Windows. |
32 bit Microsoft operating systems (2000 and up) have a 4gb virtual memory address limit - for both the ram and the requirements of Windows.
When you install 4gb, or more, depending on the system and whether you're using onboard video or not, Windows can only actually use anywhere from a little under 3gb to a little over 3gb when you install 4gb of ram. Windows itself uses up some of the virtual memory address space the ram needs when you have a 32 bit operating system in that situation.
If you want to be able to get Windows to use all of 4gb or 6gb or more in Windows 7, get a 64 bit version!
Buying OEM Windows 7 64 bit or 32 bit is the cheapest way of getting a single licence copy. It's not a retail version. You can get it on the web, or some local places that repair and build custom computer systems and have lots of parts and software sell it. OEM in this case = you get no free Microsoft phone or other technical support - you provide your own support. You can buy it from TigerDirect without having to buy hardware along with it, but otherwise you need to buy it along with something essential for a computer - e.g. a case power cord will do.
By the way, not all software that runs in 32 bit Windows will run in 64 bit Windows, and lots of program versions are STILL not compatible with Windows 7, even when they are compatible with Vista !
Most people DO NOT need more than 3 or 4 gb, and DO NOT need to run a 64 bit operating system !
Ultimate Memory Guide
How Much Memory Do You Need? etc.
Windows98 and up, to Vista, Linux, Mac
No mention of Windows 7.
How much memory do you really need?
NT Workstation and up
Windows 7 is there.
E.g. A real life example.
I tried both 3gb and 4gb of PC6400 ram on a friend's system that's running XP Home.
I bought the ram in two matched pairs at two different times for him - same maker, same non JEDEC voltage ( 2.0 ? ) , slightly different timing specs.
The bios was set right for the combo by default - I checked.
He's using a Radeon 4850 video card (wow !) , and an Athlon 64 X2 6400+ cpu (the top of the original ones) , on an Asus AM2+ mboard model that was new two years ago or less. It has onboard video but that was auto disabled when he ( I did it for him ) installed the video card.
I looked at System Information under the same conditions.
- When I installed 3gb of ram, in System information I saw there was a bit more Available Physical Memory, than there was when I installed 4gb of ram !
- The system NOTICABLY ran better with 3gb rather than 4gb !
It told the computer owner his system ran better with 3gb rather than 4, and I left only 3gb installed, but he's computer STUPID and installed the 4th module later anyway.
If you don't believe your computer could run better with 3gb than it does with 4gb with a 32 bit operating system, run some third party performance tests with 3gb and 4gb to compare the two situations.
E.g. Sisoft Sandra.
3 modules of DDR2 ram can't run in dual channel mode on most computers, but that's a very minor concern. In the real world having all the ram running in dual channel mode results in at best a few percent performance increase - it's marketing hype.
You get much more of a performance increase, if you actually have programs that run better with more ram (most people do not, after a certain amount of ram is installed), by installing more ram, or, probably, according to my experience, by installing 3gb rather than 4gb of ram (or > 3gb but less than 4gb), in a 32 bit operating system.