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DDR5-8000 CL38 first-word latency is 9.5 ns

DDR5-8000 CL38 is the bleeding edge of mainstream XMP memory in 2026 — a speed grade that only works reliably in two-DIMM configurations (one DIMM per channel) on high-end Z790 / Z890 boards with strong memory controllers. The 9.50 ns first-word latency is essentially matched to DDR5-7200 CL34; the real story is bandwidth.

First-word latency
9.50 ns
CL38 @ 4000 MHz bus
Row cycle time (tRC)
36.0 ns
tRP + tRAS
Peak bandwidth
64.0 GB/s
Per channel

Calculator

RAM Latency Calculator

MT/s
clk
clk
clk
clk

Timings are in memory clock cycles. True latency in nanoseconds is derived from the data rate.

True Latency

First-word latency (CL)

9.50 ns

Time from a read command to the first bit of data arriving.

I/O bus clock

4000 MHz

Cycle time

0.250 ns

tRCD delay

12.00 ns

tRP delay

12.00 ns

tRAS

24.00 ns

tRC (tRP + tRAS)

36.00 ns

Peak bandwidth per channel64.0 GB/s

Assumes one 64-bit channel. Dual channel doubles this, quad channel quadruples it.

How this is calculated

4000 MHz bus clock, 0.25 ns per cycle, 38 cycles of CL = 9.50 ns. Peak per-channel bandwidth is 64 GB/s — 11% over DDR5-7200 and 25% over DDR5-6400. Four-DIMM configurations almost always require backing off to DDR5-6400 or slower on this same platform, which is why enthusiast builds targeting 8000 MT/s universally use 2× 24 GB or 2× 48 GB kits rather than 4× smaller modules.

Verdict

DDR5-8000 CL38 is for enthusiasts with a good IMC-bin CPU and a 2-DIMM board. The gains over DDR5-6400 CL32 are real but modest in games; it matters most for memory-bandwidth-bound synthetic workloads.

More DDR5 scenarios

DDR5-4800 CL40
CL40 • 4800 MT/s
View details ➜
DDR5-5600 CL36
CL36 • 5600 MT/s
View details ➜
DDR5-6000 CL30
CL30 • 6000 MT/s
View details ➜
DDR5-6400 CL32
CL32 • 6400 MT/s
View details ➜
DDR5-7200 CL34
CL34 • 7200 MT/s
View details ➜

Frequently asked questions

What's the true latency of DDR5-6000 CL30?
True latency = (CL × 2000) ÷ speed = (30 × 2000) ÷ 6000 = 10 ns. That's one of the fastest mainstream kits currently shipping; most DDR5-6000 kits at stock JEDEC timings sit closer to 13-14 ns.
How do CL and MHz affect RAM speed?
Data rate (MHz) determines how much bandwidth you get; CL determines how long you wait for the first bit. Higher MHz + lower CL = more throughput plus faster access. A kit with twice the MHz and equal CL halves the true latency in nanoseconds.
Is DDR5-6000 CL30 better than DDR4-3600 CL16?
DDR5-6000 CL30 is 10 ns true latency; DDR4-3600 CL16 is 8.9 ns — DDR4 is actually slightly lower latency on that comparison. But DDR5-6000 has nearly 67% more bandwidth, which matters far more for modern CPUs, especially AMD Ryzen 7000/9000 and Intel 12th-gen+.
What are tRCD, tRP, and tRAS?
Secondary timings. tRCD is the delay to activate a row before accessing a column; tRP is the time to close a row before opening another; tRAS is the minimum time a row must stay open. All three are measured in cycles; converting to ns uses the same formula as CL.
Does faster RAM help gaming?
On AMD Ryzen and modern Intel platforms, yes — especially in CPU-bound 1080p titles where the gap between DDR5-5200 CL40 and DDR5-6400 CL32 can be 10-20 fps. At higher resolutions the GPU becomes the bottleneck and RAM speed matters less.
What is JEDEC vs XMP/EXPO?
JEDEC is the default SPD profile every DIMM boots with — conservative timings guaranteed to work anywhere. XMP (Intel) and EXPO (AMD) are overclocking profiles stored on the DIMM that you enable in BIOS to unlock the speeds printed on the heatspreader.

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