hi angelo no…different motherboard use different speeds of ddr2 memory,however within as long as your motherboard supports the specific speeds you can mix different compatible speeds of ddr2 for example i have a msi motherboard that supports ddr2 memory (667mhz and 800mhz) so allthough i am using 667mhz(pc2-5300) memory i could in theory use 800mhz(pc2-6400) memory aswell and if needed mix them however i cannot use any higher or lower speeds of ddr2 memory as my pc wouldnt support them and probally wouldnt boot ! the best method of evaluating your pc,s memory is to go to http://www.crucial.com/uk/?click=true … and run the “Crucial System Scanner tool”……this will scan your pc and return a report on the exact memory you pc supports…and since this information is gathered in real time you know its 100% correct apart from the type of memory your pc supports the crucial scan also informs you if your motherboard supp