Thanks, Dr. Dean, For the input...Motherboard-P6SET-ML, build April '99, manual says, "..supports memory chips that have EC, ECC or no EC , 66 or 100 MHZ." Running 64 megs of 100, DIMM 1, 8 megs allotted to video. Tried to install 2 other 100 mhz modules with 64 megs each, neither worked, but did work in my sons computer...AMD K6. Any idea what the SPD designation stands for? TIA..Vern The NOSPIN Group provides a monthly newsletter with great tips, information and ideas: NOSPIN-L, The NOSPIN Magazine Visit our web site to signup: http://nospin.com