System RAM

My System is a Dell XPS 8930 Model.
Service Tag HNMD243 and they Told Me it has DDR4. in it.

I know DRAM is Dynamic Random Access Memory.

But SDRAM is Synchronize Dynamic Random Access Memory so it goes at the Speed of the CPU.

I think they Told Me I have DRAM but why not use SDRAM so it goes at the Speed of the CPU?

What am I not Understanding?