Question on memory 'ranks'

[serverxeon]

What exactly is this 'rank'?
Is one rank = one stick of ram?
How do i find out what rank is a particular stick of ram?

For instance, i am looking at this... Corsair CMD8GX4M2A2400C14.

I am asking this in specific to the Ryzen's memory restriction, as I do not quite know how to pick a correct RAM for the ryzen.

Article says

Also pay attention to the type of RAM you're using. Officially, Ryzen processors only support DDR4-2667 speeds with two single-rank DIMMs. Use two dual-rank DIMMs and your maximum official RAM clock drops to DDR4-2400. With all four DIMM slots occupied, things get even worse: DDR4-2133 for single-rank DIMMs, and DDR4-1866 for dual-rank DIMMs. Unofficially you can try running higher clocks, but with four DIMMs you're likely going to get 2933 tops, and more likely 2667 or 2400.

 

[wwenze]

https://en.m.wikipedia.org/wiki/Memory_rank

 

[yusoffb01]