The easiest way to find out is to go to www.crucial.com and let it scan your pc and tell you what you have and need.
This is from the 760 manual in Dell support.
Addressing Memory Configurations
If you are using a 32-bit operating system such as Microsoft® Windows® Vista®, your computer will support a maximum of 4 GB of memory. If you are using a 64-bit operating system, your computer will support a maximum of 8 GB (2-GB DIMMs in each of the four slots) of memory.
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I hope this helps you.
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