RAM speed confusion

[garg10may]

I have windows 8.1 installed. In task manager it shows 1333MHz but CPU-z shows 667 Mhz which one is right. Also some where I read it could be 1600Mhz but I would need to change the bios settings.

I need to upgrade and buy another 4GB stick. Which one I should buy. You could see the details as in below pics.

My model is Dell Inspiron N1050

 

[gskill support]

Look in the memory tab of CPUz.

Your RAM is DDR3-1333 (667MHz) 9-9-9-24 1.50V

This is a common confusion because DDR is double data rate, so 667MHz * 2 = 1333MHz right? No, it's actually not double the actual frequency, it is double the transfer rate, so the conversion changes to MT, so it is DDR3-1333 MT but still 667MHz. Rising and falling signal edges at 667MHz, not 1333MHz one way.