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Hi,
 
i'm looking to buy an (Asus P5GC-MX 1333 motherboard) the board comes with 2 DIMM memory module slots that takes 4Gb of ram max.  
My question is, is it necessary to run the modules in dual mode 2Gb + 2Gb in each slot = 4Gb??? or could i just use 2Gb in one slot and 1Gb in the other = 3Gb??? I'm running windows XP which means it will only read 3Gb anyway, so this is where i get confused...
 
If i run 4Gb windows will only read 3Gb which in effect will not be running in dual mode because the modules are unbalanced,  
 
and if i use 2Gb + 1Gb = 3Gb again! this will be unbalanced not in dual mode,  
 
sorry for the confusion but this is the only way i can interpret it,
 
so do i have to run these modules in dual mode??? or can i just use a 2Gb + 1Gb and leave it at 3gigs???
 
 
Thanks
Musicmad

With 4gb in balanced sticks, it will read in dual channel, even if the os can't use all of it. If you put in 3gb in unbalanced sticks it won't read in dual channel.

^correct, although dual channel with an intel c2d yeilds little performance increase if any.
 
With current pricing of DDR2 though you may as well buy the 2x2gb if you want 2gb+ that is

Actually, since the MB has an Intel chipset, with 2+1GB unbalanced, it will run the lower 2GB (1+1) in dual-channel mode, and the upper 1GB (1+0) in single channel mode.  I think Intel calls this "Flex-mode" or something like that.

So what your saying is i can use 3x1Gb modules but only 2 will run in dual mode and the othere one in single mode?? Would this still give me 3 Gigs of ram to operate with though??
 
Do i have to run the modules in dual mode just because i have Dimm module slots?? or can i run 2 in dual and 1 in single as mention above
 
would there be a potential memory problem having 2Gb run in dual and 1Gb in single or would thay be fine???
 
 

If there is enough free address space then yes, you'll have access to all 3GB.
 
DIMM is not about this, so that is not an issue. The only problem is a small drop in performance. If you benchmark it, it will drop whenever it accesses data in the upper 1GB area.

And if one looks in the specs, that board only supports 2GB and no flex mode.

Just get 2 more gb of it. A 2gb ddr2 stick cost around $35, which means you're possibly inviting problems just to save a measily $17. Not worth it.

 
In correction to your misunderstood 2Gb, the board supports 4Gb of ram.. these! are the specs..
 
Asus P5GC-MX 1333 Motherboard  
Socket LGA 775 Based on the Intel 945GC(A2)/ICH7 chipsets, is built for Intel Core 2 Duo, Pentium D, Pentium 4, Celeron D processors and is compatible with Intel 05B/05A/06 CPUs. The uATX platform supports Intel Hyper Threading Technology, 1333/1066/800/533 FSB, DDR2 667/533 MHz memory up to 4GB, PCI-X x16/x1, SATA 3Gb/s, PCIe 10/100M LAN, 6-channel high-definition audio, and USB 2.0. Special features include ASUS CrashFree BIOS 2, ASUS Q-Fan, ASUS EZ Flash, and ASUS MyLogo.

So what your saying.. is, i can run 2Gb + 1Gb and still have 3 gigs to work with even though their not in dual mode??  
 
If i'm correct What you mean is, even though i have dual channel memory architecture Dimm slots on my board, its not necessary for me to run the modules in dual mode??
 
Hence i can use the 1 + 2 giving me 3gigs and this would be fine??? given the modules are all of the same speed..
 
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Sort of.  The first 2GB will be in dual-channel mode, and the last (unpaired) module will be in single-channel mode.  Everything will work fine and there won't be any problems.
 
 

Yes, but it's not something you can set -- the board detects what's installed and makes the setting automatically.
 

Yes.
 

 
So even though the MB supports up to 4Gb, but the OS up to 3Gb, i can still use 4Gb of ram in balanced modules
 
and it will run in dual mode???  
 
How can 4Gb run in dual mode if the OS only supports up to 3Gb, would'nt the last 1Gb be lost
 
Giving me only 3Gb out! of dual mode???

The dual channel mode works at a lower level than the assignment of memory addresses, so the memory controllers are first set up to run in dual channel mode.  Later in the bootup process, the BIOS assigns memory addresses, first to various hardware devices, then RAM is assigned all addresses that are left over.  Since there are only 4GB of addresses to start with in 32-bit mode, only 3GB+ addresses will be left to be assigned to RAM, but all RAM will be running in dual-channel mode.

Mondoman thanks for your extensive help in trying to get my head around this concept of memory, pretty heavy but i'm getting there..
 
also to everyone else who contributed to this post, thank you..
 
Cheers  
Musicmad