Leosghost - 10:01 pm on Jun 9, 2011 (gmt 0)
Because it will make the system unstable and you'll keep losing data that ought to be in RAM but that the RAM will be "dropping"..Old RAM ( pre DDR ) you could mix stick values without hitting problems ( most of the time ) ..it would total up the megs and run.
DDR Ram isn't so forgiving..you have to upscale all at once ..( sometimes its even better to get it all from the same maker ) ..sell your old RAM sticks..if they are hard to get ..they may be worth more than you paid for them ..and someone with a good machine ( that they don't want to "upgrade the memory on ), but bad or "flaky" RAM on a stick or sticks ..will buy it ..
An image for you ( its way more complex than this but the image will do ) imagine your data is like molasses ..you have a gallon jug ..you push it, or pour it down a pipe that is 6 inches diameter towards other pipes..matched RAM speeds is like having all the others the same diameter , like 4 x 1 and a 1/2 inch ..it will flow smooth ..and come out like it went in ..unmatched RAM speeds is like 2 x 1 inch and 2 x 2 inch ..it wont go down even if pushed the same ..the 2 x 1 inch ones wont keep up ..or the 2 x 2 inch ones will slow down ..and at the other end it will come out uneven ..and from time to time at the entrance to the pipes it will overflow a little..and some will get lost.
It isn't like that ..but you get the picture ..DDR RAM is better to match..if you want to not lose data or have wiggy things happen to the machine ..like occasionally freezing and / or reboots and /or blue screens etc etc ..or even display problems..