Should I add 3rd stick of DDR Ram

I have a motherboard that supports PC2700 DDR Ram.  I have 1 pair of matching 512 MB sticks in there for a total of 1 gig, but I also have an extra 256MB stick that just came out of another computer.  It is a single stick -- not paired.  Should I add this third stick to my system to increase the total memory, or will this slow it down b/c of the DDR technology?  Please explain.
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wlennonVP of Domestic & Int'l OperationsCommented:
griffen's reply was: >>No, the motherboard DOES support dual channel DDR.  That's why I ask.  I already have 2 slots filled with 512, but there is an empty slot and I have a spare 256 stick sitting around.<<

So, the question should be to griffen, is the 256k stick Dual Channel RAM.  As Watzman states, if it is not, all RAM will default back to DDR and not Dual Channel DDR.  

Many boards will not accept mixed memory.

My personal opinion (for what's it worth) is to just leave it out, it isn't significant enough to attempt slowing the Dual Channel down, thus defeating the purpose of having Dual Channel DDR. If it were 512K I would say give it a try.

Lee W, MVPTechnology and Business Process AdvisorCommented:
1 GB is usually pretty good for most uses... what do you do with the computer?

An extra 256 Isn't likely to help much, but if:
1) your motherboard doesn't support Dual Channel DDR, and
2) the chip is as faster or faster than your existing memory
then it shouldn't hurt adding it to the system.
griffenAuthor Commented:
No, the motherboard DOES support dual channel DDR.  That's why I ask.  I already have 2 slots filled with 512, but there is an empty slot and I have a spare 256 stick sitting around.  I understand that if the MB supports dual channel DDR, you want to install in pairs, which I did, but if that is all you should put in, why do so many have 3 slots for RAM instead of 4?  Is it better to leave that 3rd slot empty or throw it in?
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If it doesnt support Dual Channel, then just add the extra stick, as long as it can cope with the FSB, it should work fine, I have a few boards here that uses 3x512 and 512+256+256

But as lee said, 1GB is more than what most would need, unless you do heavy duty graphics or editing.
leew and robertdims are right, if you need the extra ram just bicycle it into your mobo and enjoy the extra memory. but if you do not realy need it, leave it out and use it in another machine.

I would not add it.

First, unless you are doing something very unusual, it won't make any difference in performance, even going from 512 megs to 1 gig doesn't do much for most people (there are lots of exceptions if you are doing gaming, CAD, and some other specific applicatations, but I'm being general here)

Second, if your system uses dual channel memory, which we don't know, it will revert the system to single channel operation, cutting the speed of the memory sub-system in half.
My mistake, I misread the 'it DOES support dual channel' bit, if it does and your two sticks are already in DC mode, then yes it would degrade by adding the extra stick, no matter what size it is.

Some boards do come with 3 slots where 2 can be use in dual channel mode.
If the stick is as fast as the other sticks... go ahead and add it... if not, you may be introducing problems in to your system and or making it slower.  The extra memory won't give any noticable aspeed increase.

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