The RAM is either single, dual or quad rank.
The CPU/motherboard will be dual or triple channel depending on the generation, and then quad channel for higher-end I've seen.
The motherboard should tell you how many "ranks" you can have per channel. IE: Some SM boards allow 8 total, so if you have 4 slots and you use 4x Dual Rank = capacity, but if you use 2x Quad Rank = capacity. Some of the HP ram I've purchased in 8gb sticks is single rank, so it just depends which server it came out of --- google the part# to get the "ful specifications". I have HP RAM in a # of my SM boards, same with Samsung, Kingston, Micron, and Hynix.
I recently made the mistake of forgetting to check, and ended up with a ton of 4gb quad rank
Luckily at $12/stick it's not too huge of a mess for me.