I would appreciate if someone could tell me the EXACT RAMBUS memory that is used in the DELL mobo 4H665, from a OPTIPLEX GX400. I need to know if it is 600, 800,followed by a 40 or 45, 8 devices, 16 devices, ECC or NON-ECC. In the past I have used 800-40 or 45 from 64 MB up to 256 MB per stick in slots 1 and 2 or 1 trough 4 in either mixed pairs or all the same. There was never an issue with these choices. I have 3 mobos 6E153 from a PRECISION330. This board REFUSES to accept the same sticks I have always used. Both boards result in the same failure. I do not know if these boards are bad or if they use different sticks. The 800-45 sticks are 16 devices. The 600-53 sticks are also 16 devices. I have a matched pair of 4 800-45 that are 8 devices. I was told that these boards will not work with 8 devices. Is that correct? In the past with the 400 board I have disregarded the # of devices, never knowing what the 8/16 represented. Never an issue. I have 2 400 boards coming for my rebuilds. Any accurate and informative info welcome. Please explain this in simple terms as my knowledge is limited.