Hi... wife wants to toss her old Dell 1545, but I want to set it up as a spare backup machine running LInux; I'd like to max it out with some components I have around. System max is 8 Gb, and I'd like to stick a single 8 Gb stick in slot 1, but the RAM I have is 1.5 v, and the original system RAM is 1.8 volt. Will I fry the lower voltage memory and/or damage the mobo? thanks!
The rams these days won't be as resilient as an 1.8v stick of ram, in fact the manufacturing process for a 1.8v is different than one with 1.65 or 1.5v, better binning with latter generation ram chips. Try and source the exact same stick of ram for your laptop or if possible look out for older G.Skill ram kits. Mind sharing an image of the sticker on the side of your existing ram stick?
One more thing to note, you might not even be able to get to 16GB since your chipset might either burn up(due to the stress) or that it won't recognize more than 8GB's of ram without throwing hiccups. My search shows that your laptop came equipped with a Core2Duo, if so, then yeah 8GB is it's max. To add, if your laptop is DDR2, you can't drop in a DDR3 or latter generation stick of ram. So in short, you're not going to find SO-DIMM's for 8GB under DDR2 and your laptop will not go beyond 8GB, if my research is correct.
They are not compatible with each other.
So if your laptop supports DDR2 ram, then you can not physically insert DDR3 ram into the ram slot. Physically impossible.
If you try to force DDR3 ram into DDR2 slot, you'll damage either ram module or ram slot (possibly both).