Hello,

My name is Mike, advertisement advertisement lip service lip service. I've read your post and wanted to offer some assistance. To answer your questions 1) Yes, you should be able to add a pair to the existing chips as long as the board supports it (e.g. there are available slots). 2) In theory, yes you can put 400mhz chips in systems, however it will lead to problems in the future and that's if the system recognizes the chips at all so I wouldn't recommend it. Another thing to keep in mind is that the memory will only run as fast as the slowest chip installed. So, if you put 2 sticks of 667Mhz chips in the system with 2 sticks that are running 533Mhz, all of the chips will run at the lower speed, 533Mhz. If you have any other questions for me you can reach me at customer_advocate@dell.com with my name and this description in the subject line, ATTN: Mike B. (Dell memory speed), and I'll get back to you ASAP.

Thanks,

Mike.
Dell customer advocate.

PS. Support your local businesses and only use Dell computers for boat anchors, targets in mortar exercises and games of "lets smash a dell to tiny pieces with a baseball bat"