Memory Question

[jimras]

I recently upgraded my computer and I installed 2 Gig of Memory at the time and all worked fine.

I saw on Sunday that Tiger direct had the memory on sale that I just bought a month ago so I bought

me 2 more Gigs ($34 after rebate) and installed that too. The motherboard has four slots and now they

are all full. The memory sticks are all the same.....Corsair TWINX PC6400 DDR2 800 MHz ....four 1 Gig sticks.

The MoBo will accept up to 16 Gigs of memory, from what I read. It is an Asus M2N-SLI nForce 560 Socket AM2 board

and I am running an AMD Ahtlon 64 X2 6000+ chip at 3GHz and I have XP Pro SP3 for my OS.

Now....here's the thing. The BIOS says that there are 4 Gig installed but when I check thru Windows / Control Panel / System / it

shows that I have 3.25 Gig of memory. I remember reading that XP Pro could/would use up to 4 Gig of memory so why isn't it showing

up there? Is something wrong or out of whack?

I would appreciate any help or advise that you experts could offer on this.

jim

[Besttechie]

I assume you are running a 32bit version of Windows XP, if that is the case, Windows will not address more than the 3.25GB it is showing. In order for it to recognize the full 4GB of RAM you will need to get a 64bit edition of Windows.

B

[jimras]

I assume you are running a 32bit version of Windows XP, if that is the case, Windows will not address more than the 3.25GB it is showing. In order for it to recognize the full 4GB of RAM you will need to get a 64bit edition of Windows.

B

OK then. That makes sense.

Thanks BT...appreciate the quick reply.

jr

[shanenin]

I found this explanation by the author "AnonymousCoward" on another forum. He(she) did a nice job of explaining it.

All major 32bit operating systems can address 4GB of RAM. In fact most can address far more (using technology called PAE that's been available in Intel CPUs for several generations now). This is how Windows Server 2003 Data Center Edition can address 64GB of RAM, even though it's a 32bit OS.

Now, for Windows 2000 / XP / Vista, Microsoft has put in a hard coded limit of 4GB of address space. Partly to sell higher end OSes, and also partly because a lot of consumer drivers where never written to cater for addresses beyond the 0xFFFFFFFF boundary and would thus blue-screen the machine (in XP prior to SP2 you could use /PAE to get >4Gb of addresses)

OK, so why can Windows only see something less than 4GB of RAM? Because the BIOS allocates some memory addresses to hardware devices that are memory mapped. This includes various video cards, RAID controllers and sundry other devices. How much depends on what the hardware device needs/requests. Those addresses are *not* available to Windows to use to get at memory, and becuase Windows XP / Vista can only use addresses below the 4GB boundary, it can't address that RAM.