[/img]i have a kingston 512 mb 400 mhz with CAS timing of 3-3-3. i added a transcend 512 mb 400 mhz with CAS timing of 2.5-3-3.
i placed them first in dual channel mode just for fun, surprisingly my mobo actually recognizes it as dual channel!! how is that possible!! i ran CPU-Z and they also confirmed it to be dual channel. i was worried and then switched to single channel and there was a screen saying that it was not on their optimum position. did this ever happen to anyone? should i place them in dual channel mode??
the FSB RAM reads 5:4, is that good? previously it was 1:1 (with only the kingston)
5:4 isn't as good as 1:1, obviously. It seems as if adding the Transcend memory stepped it down. Are you overclocking? If both modules are rated at DDR400 it should be running at 1:1 unless you are overclocking. At any rate, dual channel is better than single channel, even if it steps it back a bit.
Verify that they are both at DDR400, if so it should remain 1:1 (which is better as bagg said). If you run two sticks of RAM with different speeds or timings, they will automatically adjust to the lowest of the two.
Example, if the second stick is actually only DDR333 then the Kingston will be clocked lower to match. Same with the timings, if the new one is 2.5 and the Kingston is 3, the new one will run at 3 as well.
You may have to adjust it in your bios. Sometimes the rated speed or timings aren't automatically detected properly or are clocked lower by default for max stability and compatibility.
While it's possible to run dual channel with different manufacturers I wouldn't recommend it. There is a lot of things that can go wrong at DDR400+ so that just adds one more variable to the equation. I don't think manufacturers selling matched DIMMs for dual channel are just doing it for marketing purposes but I guess you never know!