4GB RAM with XP and Vista - fully utilized or some gone to waste??

You simply can't use it all.  With a 32-bit OS, you can only access 4G total address space and some of that space is used for graphics card memory, and other devices.

 

The page file is for virtual memory and resides on the disk.  Maybe you are asking if the RAM can be accessed in some other clever way to make RAM disks (like the in the old EMM and XMS memory days).  The answer is no, it is just plain not used.

 

That said, I wouldn't waste money buying anything smaller than 1G modules, so 4x1G is not a bad configuration.  Maybe they can be used later. 

 

Peter 

Only sure way to address the full 4 gigs of memory is to get the 64 bit version of the operating system. Once you do, than you will have to download the Microsoft Hotfix and have it waiting some where on the desktop for later install.

If you have SP-1 already installed, the Hotfix will not be necessary since it comes with SP-1 already. If not, then you have to download the Hotfix

Microsoft link to the 64 bit OS and the difference between a 32 and 64 bit Windows

http://support.microsoft.com/kb/946765

You will than turn off the system, remove two sticks of memory, leaving you with 2 Gb total. Boot back up, install the Hotfix, than turn off the system and reinstall the other 2 gb of memory into the proper slots. Boot back up, now you are done.

www.newegg.com  has the OEM 64 bit OS for about $100.00

Hotfix download link
http://support.microsoft.com/kb/929777  

If it's a Dell sold Vista on a Dell system, per Bill's post here, you're entitled to the x64 version of Vista.