....?

The E7400 is a 45nm processor, which will not work with the Dimension E520.

The best Core 2 Duo you can go with is the E6700.

Or you can upgrade to the Core 2 Quad Q6600 or Q6700. They will work. Decide this quickly, as Intel will be phasing them out soon.

The E7400 is a 45nm processor, which will not work with the Dimension E520. The best Core 2 Duo you can go with is the E6700. Or you can upgrade to the Core 2 Quad Q6600 or Q6700. They will work. Decide this quickly, as Intel will be phasing them out soon.

Why do you say the 45nm processor will not work - the 45nm is the process used to manufacture the chip but it still is a socket 775 interface?  I am asking because I also am planning to upgrade my E520 from the E4300 to E7400 and believe it would work

Even though the socket type is the same, the voltage requirements are not - it will not work.

Thank you for the clarification - I hadn't considered the voltage and would have made a bad purchase.

Can anyone recommend any E520 compatible Core 2 Duo processors other than the E6600 and E6700 mentioned in other posts?  I have never upgraded my CPU before so this is all very new to me.

Thanks in advance for any replies.

I did some additional research to see the voltage ranges in the socket LGA775 processors and have to admit that I don't understand the difference in the voltages and how to determine if one is compatible or not.  The E4300 shows the voltage range is 0.85V-1.5V so does that mean that the replacing cpu would have to match it exactly? 

The E6600 and E6700 shows their voltage range is 0.850V-1.3625V but several posts have indicated they would be compatible.

Again, any information would be appreciated.

FYI: This link is from an Intel webpage showing how the CPU's compare.

http://ark.intel.com/Compare.aspx?ids=28024,29753,30781,32242,27248,29754,27249,29755,30782,30783,27250,27251,30784,30785,35348,

36463,36500,36503,41495,34442,33909,35070,33910,33911,35605,