I am upgrading an Acer T690, mobo E946gz, bios r01-b4. This machine has two DDR2 RAM slots. It came to me with Acer-branded 512kb RAM modules. The computer seems to work correctly, but will only boot if an original 512kb module is in one of the slots. It recognises any additional memory and appears to use it correctly, but will not boot if an original Acer module is not present. I have tried it with 1 and 2 gb modules from other manufacturers. These work fine, also for booting, in two other test computers. There is no indication that these modules are faulty and the Acer also works fine with them, it just won't boot if they are the only RAM present. Can anyone explain what is going on here?