I have an older Toshiba Satellite M505D s4000. Currently it has 4 G Ram ( 2 in each slot). All sources say I can upgrade to 8 G ( 4 in each slot) but I can't seem to locate a suitable set of chips using the "find" tools at the various vendors. Can this actually be done? who sells this item ? needs: sodimm 64bit 1.8 v pc2-6400 ddr2.