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DDR4 vs DDR5 latency: higher bandwidth doesn't always mean lower latency

DDR5 roughly doubles the peak bandwidth of DDR4 (from ~50 GB/s to ~100 GB/s per module), but true latency measured in nanoseconds is nearly unchanged. A DDR4-3600 CL16 kit has about 8.9 ns of true latency. A DDR5-6000 CL30 kit has about 10 ns. The DDR5 kit is slightly slower per access but can handle twice as many concurrent transfers.

Hardware tier
RAM
System memory and DIMMs
Topic focus
DDR4 vs DDR5 latency
ddr4-vs-ddr5

How this is calculated

CAS latency (CL) numbers are in clock cycles, not nanoseconds. DDR5 runs at higher frequencies, so its cycles are shorter. CL30 at 6000 MT/s is 10 ns. CL16 at 3600 MT/s is 8.9 ns. The DDR4 kit has lower absolute latency. But DDR5 runs at double the transfer rate, so for workloads that are bandwidth-bound (video editing, scientific computing, AI inference), DDR5 wins. For latency-sensitive workloads (games, databases with random access patterns), the difference is small and either generation at the same tier performs similarly. The real gains from DDR5 come from higher capacities per DIMM and better power efficiency, not lower latency.

Verdict

DDR5 does not meaningfully reduce memory latency compared to high-end DDR4. It wins on bandwidth and capacity. If you're building a gaming PC, a fast DDR4 kit is still competitive with mainstream DDR5. If you're building a workstation or server, DDR5's bandwidth advantage is worth the upgrade.

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DDR5-6000 CL30 latency
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DDR4 vs DDR5 comparison
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Frequently asked questions

How much faster is L1 cache than RAM?
Roughly 40-60x faster for random access. L1 cache access is about 1 ns; DDR5 RAM is about 50-80 ns end-to-end including controller overhead. That's why keeping hot data in cache dominates real-world CPU performance.
Is NVMe SSD faster than RAM?
No. NVMe is fast for storage, but for random access its latency is around 50-150 µs versus RAM's 50-80 ns. That's a 1,000x gap. NVMe beats RAM only on raw capacity and persistence, never on latency.
Why is HDD so much slower than SSD?
A spinning HDD has to physically move a read head to the right track and wait for the platter to rotate into position, typically 5-15 ms per random access. An SSD has no moving parts and returns data in under 100 µs, roughly 100x faster for random reads.
What's the point of L3 cache?
L1 and L2 are tiny (KB to low MB) and per-core. L3 is much larger (tens of MB) and shared across cores, acting as a buffer before requests go to main RAM. It catches data evicted from L1/L2 and data shared between cores.
How many nanoseconds is one CPU cycle?
At 4 GHz, one cycle is 0.25 ns. At 5 GHz, 0.2 ns. Cache hits are measured in single-digit cycles; main memory access costs hundreds of cycles, which is why optimizing for cache locality matters enormously in performance-critical code.
Does DDR5 have lower latency than DDR4?
Not usually at the same relative tier. DDR5 improved bandwidth and capacity significantly, but true latency (in ns) for mainstream kits is similar to late-stage DDR4. The gains from DDR5 come from bandwidth and larger capacities, not lower memory latency.

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