kulmi,

Just to confirm, are you asking for the largest processor supported on the R420? If so that would be the Intel 2.8GHz E51410V2 (part # 6N2HW). Now if you are asking how to max out the cores, you would do so in the BIOS under Processor settings, as seen on page 26/27 here. 

Let me know if this helps.

@DELL-Chris H ​ Hi, are you sure about Intel 2.8GHz E51410V2 ?, because yes is in a way   compatible but looks like for the T420  better CPU are  Intel® Xeon® processor E5-2400 and  E5-2400 v2 product families, anyway apparently the better for the T420  are a couple of   Intel Xeon E5-2470 v2

https://www.cpubenchmark.net/compare/2715vs3068/Intel-Xeon-E5-2470-v2-vs-Intel-Xeon-E5-2450-v2

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://i.dell.com/sites/content/shared-content/data-sheets/en/Documents/dell-poweredge-t420-technical-guide.pdf

Hi,

the CPU Chris wrote is the maximum supported not the maximum that would be working.

@Dell-Martin S​ Ok, just curiosity which is the difference between maximum supported and the maximum which can work?, thank you very much

The maximum we support is what Dell has tested on the server, and the other would be maximum that you can get to work, but isn't tested.