Types of RAM specs

[Moswenw]

I am looking into a building a new PC and I getting confused about what type of RAM to buy. I keep seeing two different sets of numbers and I am confused what each means.

Example:
motherboard says specs: Memory Standard - DDR4 2133

Ram title says: DDR4 2133 (PC4 17000)
or DDR4 3200 (PC4 25600)

Can someone please explain what the numbers mean i.e. DDR4 2xxx vs (PC4 1xxxx)? Thank You

 

[Petrossa]

Those numbers refer to the speed of the RAM. Your board officially supports DDR4-2133MHz RAM in it's stock state, but might allow you to use DDR4-3200MHz RAM by overclocking.
The PC rating is another way of expressing the exact same thing.
Perhaps this article will shed some light on your questions: http://www.alphr.com/features/230484/what-does-ram-speed-mean