I have an Inspiron 560S that came with 4GB DDR3 1066 MHz (PC3-8500), 2 x 2GB.
I wanted to upgrade to 8GB and found a good deal online for these 1333 MHz (PC3-10600): http://www.crucial.com/store/partspecs.aspx?imodule=CT2KIT25664BA1339. My plan was to install 4 x 2GB of those new ones and use the original modules somewhere else.
I got two kits of the model above - at my own risk, I knew - and now I know for sure they DON'T WORK in my computer. It just beeps twice when powered up, which according to the manual is for "memory not recognized" or something like that. I tried the four new modules in different combinations, alone, in pairs, etc., even mixed with the old ones (which always work except if there is any of the new modules installed).
What I found strange is that this other model below, also from Crucial and showing the exact same parameters, is said to work with my computer model:
Module Size: 4GB kit (2GBx2)
Package: 240-pin DIMM
Specs: DDR3 PC3-10600 • CL=9 • Unbuffered • NON-ECC • DDR3-1333 • 1.5V • 256Meg x 64
Now I'm concerned that it might not be sufficient to get more memory with the same parameters of the original ones, even from a brand like Crucial, because the motherboard / chipset / bios is looking for something more...
Please, I would appreciate any help!
Before returning them I gave Crucial (and Dell...) one last chance and re-flashed the BIOS. Guess what? Now they are working. At 1066 MHz, but at least working. Just for the record.
Wow, sometimes I have to wonder about Crucial. I can see no differences at all. My suggestion would be to call them. If nothing else, they do guarantee their stuff and have a no-questions-asked return policy.
Please post back and let me know if you need more help.