Yesterday, I discovered that my friend laptop - a BENQ brand - has 1x1G + 1x2G RAM modules. Therefore, your saying that the system cannot run 2 different RAM modules seems not correct. You can run different modules, on either channel. 1x1GB on Channel 0 and 1x512MB on channel 1 for example. You can't put 1x1GB+1x512MB on channel 0 and the same on channel 1, the mismatch will cause the bus to drop to single channel mode. It depends on the chipset too, on some systems you must match speed AND size to operate in dual channel mode. My wording was off is all, you just can't run in dual channel mode with mismatched RAM.