Is DDR5-4800 CL40 memory good? Nanosecond latency and JEDEC specs explained
DDR5-4800 CL40 is DDR5's entry point, higher bandwidth than DDR4 but worse raw latency. Useful as a price-performance floor on a new build and an easy XMP target to overclock past.
DDR5-4800 CL40 is the JEDEC baseline spec every Intel 12th-gen, 13th-gen, and early AMD AM5 platform validates against. Its 16.67 ns first-word latency is actually slightly worse than a tight DDR4-3600 kit on paper, which is why early DDR5 adopters often didn't see an immediate performance jump in latency-sensitive workloads.
By TechCompare · Updated
Calculator
RAM Latency Calculator
True Latency
First-word latency (CL)
16.67 ns
Time from a read command to the first bit of data arriving.
I/O bus clock
2400 MHz
Cycle time
0.417 ns
tRCD delay
16.67 ns
tRP delay
16.67 ns
tRAS
32.08 ns
tRC (tRP + tRAS)
48.75 ns
Assumes one 64-bit channel. Dual channel doubles this, quad channel quadruples it.
How this is calculated
At a 2400 MHz bus clock, each cycle is about 0.417 ns, so 40 cycles of CAS latency lands on 16.67 ns. Row cycle time (tRC = tRP + tRAS) comes in around 48.75 ns. Bandwidth is the real headline: 38.4 GB/s per channel means a dual-channel kit delivers 76.8 GB/s of peak memory bandwidth, roughly 50% more than a DDR4-3200 dual-channel setup.
Verdict
At a 2400 MHz bus clock the 40 cycles of CAS lands at 16.67 ns first-word latency, which is actually worse than a tuned DDR4-3600 CL16 kit's 8.89 ns, and tRC sits around 48.75 ns. The win is bandwidth: 38.4 GB/s per channel sums to 76.8 GB/s dual-channel, ~50% more than DDR4-3200 dual-channel. That's why early DDR5 adopters saw a bandwidth uplift in productivity workloads but no latency win in CPU-bound games. XMP and EXPO are optional memory profiles, and firmware may leave the system at the safe JEDEC floor until you select one in UEFI.
More DDR5 scenarios
Related guides
Frequently asked questions
Is DDR5-4800 CL40 too slow for modern gaming?
What is the nanosecond latency of DDR5-4800 CL40?
Why is DDR5-4800 CL40 the JEDEC default?
Does my DDR5 boot at its rated speed automatically?
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