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DDR3-1600 CL9 first-word latency is 11.25 ns

DDR3-1600 CL9 is the JEDEC DDR3 high-performance standard — the spec Sandy Bridge through Haswell-era Intel and FX-era AMD builds were optimised around. Its 11.25 ns first-word latency is slower than modern DDR4 and DDR5 but still benchmarks surprisingly well for pure single-thread workloads on older platforms.

First-word latency
11.25 ns
CL9 @ 800 MHz bus
Row cycle time (tRC)
41.3 ns
tRP + tRAS
Peak bandwidth
12.8 GB/s
Per channel

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

True Latency

First-word latency (CL)

11.25 ns

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

I/O bus clock

800 MHz

Cycle time

1.250 ns

tRCD delay

11.25 ns

tRP delay

11.25 ns

tRAS

30.00 ns

tRC (tRP + tRAS)

41.25 ns

Peak bandwidth per channel12.8 GB/s

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

How this is calculated

800 MHz bus clock (DDR3's effective half-rate), 1.25 ns per cycle, 9 cycles of CL = 11.25 ns. Per-channel bandwidth is 12.8 GB/s — half a typical DDR4-3200 kit. tRC is a long 41.25 ns, reflecting the looser DDR3 row-cycle timings. Kits with CL7 or CL8 exist but are marginal and rarely stable on JEDEC voltages.

Verdict

DDR3-1600 CL9 is the baseline DDR3 spec to compare any legacy upgrade against. Still a useful reference for understanding how memory latency has evolved — DDR5-6000 CL30 ships the same 10 ns first-word latency while delivering roughly 4× the bandwidth and 2× the capacity per DIMM.

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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