Hi all I've a 1066MHz FSB Intel Core 2 Duo E6400 system with 1GB (512MB x 2) 533MHz DDR2 RAM. I'd like to add 1GB RAM and was going to get another pair of 512MB 533MHz DDR2 RAM. However, a friend has just offered me a pair of 512MB 667MHz DDR2 RAM cheaply. I originally planned to stay with 533MHz RAM so as to keep a synchronous 1:1 FSB/RAM relationship for best performance. Now, I wonder if mixing a pair of 512MB 533MHz DDR2 RAM with a pair of 512MB 667MHz DDR2 RAM will have a negative performance impact. I understand that such a combination runs at the lower 533MHz memory speed which is fine but since the 667MHz RAM will need to use a 5/4 divider and also has different timings, I'm a little concerned that performance will suffer compared to having identical 4x512MB 533MHz DDR2 RAM. No overclocking is planned. Your comments, please! Thanks.

All RAM will run at the speed of the lowest rated stick(s). In other words, since DDR2-533 can't run as DDR2-667, the system will automatically force the DDR2-667 to run as DDR2-533.

Thanks for your prompt reply, jam. A quick question about timings. Under CPU-Z SPD, the 533MHz RAM has two timings sets - 266 MHz and 200 MHz. Does it mean that, if I use CPU-Z on the 667MHz RAM and it has a 266MHz timings set (in addition to 333MHz timings) which is identical to that for the 533MHz RAM, things should be alright?

Unless you configure them manually, timings will be auto-selected based on the SPD info.