https://www.pcgamer.com/what-is-ram-random-access-memory/
Understanding memory speeds and timings:
Most RAM comes with an advertised clockspeed and four timings, so you might see something like the above DDR4-2400 15-15-15-39 kit. The speed is the easy part, that's the number after DDR4, except that's the speed in mega-transfers (MT) per second. So DDR4-2400 means 2400 MT/s, because DDR memory transfers data on both the rising and falling clocks, but the base speed is half that value—1200MHz in this case. The timings are listed as: CL-tRCD-tRP-tRAS, and are the number of memory clock cycles required for each operation.