📖 The Complete DDR4 / DDR5 Memory Latency & Subsystem Guide
1. True Latency (ns) vs Transfer Frequency (MT/s)
CAS Latency (CL) only measures clock cycle delay, not absolute time. True latency in nanoseconds is calculated as t = (CL × 2000) / Frequency. For instance, DDR5-6000 CL30 and DDR4-3200 CL16 both achieve an identical 10.0ns first-word access time, while DDR5-6000 CL36 has a slower 12.0ns response.
2. The AMD Ryzen AM5 1:2 UCLK Divider Penalty
On AMD Ryzen 7000, 8000, and 9000 processors, running memory speeds above 6000 MT/s causes the memory controller (UCLK) to automatically switch from a 1:1 synchronized ratio to a 1:2 halved ratio, introducing an immediate +10ns to +12ns system latency penalty unless running extreme 8000 MT/s kits.
3. The Crucial Impact on 1% Low Gaming FPS
While average FPS is predominantly GPU-bound, 1% low and 0.1% low frametimes in CPU-bound esports titles (CS2, Valorant, Warzone) are heavily dictated by memory latency and secondary sub-timings (tRFC and tFAW).