mean Dual Channel. For Dual Channel all pairs of sticks must be the same size and type of DIMMs. If there are four memory slots the pairs do not have to match. You can have a pair of 256's and a pair of 512's.
Since you have a Dell Dimension, why not go to http://www.crucial.com and identify your computer model and let them tell you your options?
I believe that http://www.mushkin.com offers the same service now.
Hello, I'm looking to upgrade to 1GB of RAM from 512MB. Currently, I have 2 256MB cards installed. Would installing 1 512MB card ruin the Dual Line configuration, or would it be okay? Also, any recommendations as of brands, websites to buy from, etc. Thanks
P.S. I have a Dimension 4700. Thanks for the help.