enabling ddr on epox motherboard.

You have your nomenclature wrong - you really want to know how to enable dual-channel operation.  You need to post which model motherboard you have, not just Epox.  If this motherboard supports dual-channel, you will need matched RAM modules, which mean they must be the same size, speed, and latency, at the very least (and even then, that may not be enough; you may need pairs sold as dual-channel kits).

As Callandor noted, your terminology is wrong -- you clearly mean that you want to "enable" dual channel operation.   The answer is simple:  with the modules you have, you can NOT do that, no matter which motherboard model you have.   Dual channel operation requires pairs of identically spec'd modules (they don't necessarily have to be purchased in pairs -- but they must have the same specs;  the pairs are sold as a simple way to "guarantee" you get identically specified modules).

You have 3 DIFFERENT modules -- so there is NO combination of them that will work in dual channel mode.   Further, you indicated your board has 3 memory slots -- in that case it clearly does not even support dual channel operation (since dual channel mode operates in pairs, any board that supports it will have an even number of memory slots).

... if you meant that you had 3 memory modules, but your board actually has 4 slots, then you may be able to configure it to work in dual channel mode => but as I noted above NOT with your current memory modules.   As Callandor suggested, post the exact model of your motherboard and we can tell you if it's possible.

The best (and an absolute requirement as written by others) for dual channel is that you have matched dimms.
I've had kingston modules that gave problems with dual channel (even if those were certified). Dual channel puts more stress on the dimms. I've bought a second pair of those - and never had problems with them (on the same motherboard).

The other dimms are running 100% stable in an Athlon 2600 machine.

You may be lucky while mixing different branded dimms - be sure the timings of the dimms are the same. Eg. DDR400 & 3-3-3 timing for each bank (one pair of dimms is called a memory bank).

To try those dimms it's best to use the memory test you can also find on the knoppix linux cd's. (memtest86)
It can be downloaded at: http://www.memtest86.com/ and just be written at a floppy. It's small, fast and one of the best testing programms i know. I've never had memory errors but memtest86 found the errors with the kingston dimms! (i just started to write about this minor problem at the beginning of my message).

Memtest86 can also be found on various linux distro's - just give it a try! It's one of those free tools you'd like to know about.

Never seen a Socket A (Athlon XP) mobo that supports dual channel memory.  Could be because there aren't any.  Additionally, a mobo that supports dual channel should have 4 memory slots, not 3.

DDR is simply Double Data Rate RAM.  It is used on motherboards that require DDR RAM and which may have memory configured to single or dual channel.  Some Athlon 64 motherboards support dual channel DDR RAM.

So bottom line is that your mobo probably uses DDR RAM and RAM is certainly single channel.

Do not try to insert DDR RAM into a motherboard that requires SDRAM.  SDRAM modules and slots have 2 notches while DDR modules have only one notch.

" Never seen a Socket A (Athlon XP) mobo that supports dual channel memory"

Cmon willcomp, they are all over the place, look at ASUS, ABIT, you name it, they do dual channel.

Anyway, to answer the question, put all the chips in the motherboard.  Does it run reliably?  If so leave it as is.  The minor speed enhancement you might get from exactly synchronizing your ram in pairs is not worth the current cost of RAM.  You would have to get another 512 DDR 400 exactly matched to the first, and that will cost you more than the MB and CPU is worth, in all likelihood.  If it runs with these 3 RAM chips, run with it, and save the pennies for a quad-ram 64 bit board coming out next year.

How about this Memory Tweaks from EPOX,

http://www.epox.com.tw/eng/products_feature.php?serno=20

http://www.epox.com.tw/eng/products_feature.php?serno=14

http://www.epox.com.tw/eng/products_feature.php?serno=36

Regards,

Engineer_Dell

Had head straight up rear end on this one.  Yes, nForce 2 ultra chipsets do support dual channel and motherboards using that chipset also have 3 DDR RAM sockets.

First of all many thanks for all the replies you guys have posted. I never had so much attention before :)))
My motherboard model is Epox 8K9A2+. It definitely has 3 DDR slots, not 4.
Please let me know if I can use the dual channel functionality of DDR400 chips on this motherboard (I realize that I have to get identical pairs and the ones I have will not work in this manner.)
Please also let me know how I have to set it up so that it would work with the dual channel mode.

Many thanks indeed.

I see.
many thanks.