Which Number In The Ram Is The Important One?

Hello everyone, I hope all of you are feeling great.

I have a PC with DDR3 4GB ram, and I am planning to buy another 4GB ram but I want to make sure which number in the new ram should be identical with the old one, because I’ve been searching about this serial: “KHX21C11T3K2/8X” which wrote in the ram as picture below, but I didn’t find any kind of rams with this serial, so I became confused about this number, so I made a discussion here.

[U][B]( Old ram specification )[/B][/U]

Thank you for your time.

Just buy DDR3-1600 1.5V memory and it should work.