Platforms
A Higher CAS Cycle Count Can Represent a Shorter DRAM Interval
A higher CAS latency cycle count can represent a shorter time interval when the memory clock is faster. For stipulated operating pairs, DDR5-4800 CL40 gives about 16.667 ns, while DDR5-5600 CL46 gives about 16.429 ns. Compare CL multiplied by the full memory clock period. This calculation describes the CAS-derived read-command timing component; it does not predict processor memory-access latency or AI workload speed.
Separate data transfers from full clock cycles
CAS (Column Address Strobe) latency, abbreviated CL, is a memory-clock cycle count associated with a DRAM read. CL46 means 46 memory clock cycles, rather than 46 nanoseconds or 46 data-transfer intervals. Comparing two CL counts requires knowing how long each counted cycle lasts.
DDR means double data rate: data transfers occur on the rising and falling edges of the clock. MT/s means a decimal million transfers per second. Consequently, a DDR operating rate of 4800 MT/s corresponds to a 2400 MHz memory clock. The transfer rate and clock frequency are different quantities.
The two-edge mechanism is the reason the full clock period matters. At 4800 MT/s, consecutive data-transfer opportunities are about 0.208333 ns apart, but one complete memory clock cycle lasts about 0.416667 ns. CL counts the latter. Treating the transfer interval as a full cycle halves the calculated timing incorrectly.
Convert the paired operating values to nanoseconds
Let R be the numerical DDR data rate in MT/s. The corresponding memory clock frequency is R / 2 in MHz. Since a nanosecond is one billionth of a second, the full clock period is 1000 / (R / 2), or 2000 / R, in ns.
Multiplying that period by CL gives the CAS-derived interval: CL × 2000 / R ns. Use a rate and cycle count belonging to the same DRAM operating point. A rated maximum from one description and a timing count from another operating state do not form a valid pair.
At an unchanged clock period, a higher CL gives a longer component. Across different clock periods, compare the products. Equivalently, compare CL / R for the two pairs; the common factor of 2000 does not change their ordering.
CL-52: six more cycles, a shorter interval
Consider two fictional host-memory offers with the same installed capacity and populated processor-channel count. Stipulate that both complete configurations are supported. Offer A operates at DDR5-4800 with CL40; offer B operates at DDR5-5600 with CL46. These are paired actual operating inputs for the example, rather than module labels or proposed settings. No real server is specified.
For A, the memory clock is 4800 / 2 = 2400 MHz. Its full period is 2000 / 4800 = 0.4166667 ns. The CAS-derived component is therefore 40 × 2000 / 4800 = 16.6666667 ns, or about 16.667 ns.
For B, the memory clock is 5600 / 2 = 2800 MHz. Its full period is 2000 / 5600 = 0.3571429 ns. Its component is 46 × 2000 / 5600 = 16.4285714 ns, or about 16.429 ns. The displayed periods are rounded; the results use the unrounded quotients.
B has six more CL cycles, yet the calculated component is approximately 0.238 ns shorter. Its CL count increased by 15 percent, while its clock frequency increased by about 16.67 percent. The shorter cycle duration more than offsets the extra cycles. The component falls by about 1.43 percent; that percentage describes this calculation alone.
A buyer who rejects B solely because 46 exceeds 40 has reversed this particular comparison. The corrected conclusion is that B has a slightly shorter CAS-derived component under the stipulated operating pairs. The calculation supplies no overall performance ranking or reason, on its own, to pay a premium.
Read a documented module pair without assuming server support
Kingston's KSM56R46BS8-16MH datasheet provides a real example of the notation. Revision A, document 4812048A dated May 26, 2026, describes a 16 GB DDR5-5600 CL46 registered ECC module and explicitly lists CL as 46 cycles. It also states an SPD-programmed timing of 46-45-45 at 1.1 V.
Those paired 5600 and CL46 fields explain how to read a module specification. They do not establish that a particular server supports the module, that an offered population operates at that pair, or that offer B uses this part. For an actual offer, obtain the applicable whole-system support reference and the paired operating rate and CL from its configuration owner.
References: [CL1]
Use the result to ask the next buying question
Kingston's October 2025 consumer CAS explainer presents this conversion under total or true latency. Here the quotient is deliberately limited to the CAS-derived read-command component. Its inputs supply no controller queueing time, other DRAM timing or complete processor-to-memory path. They also supply no application behavior. It cannot calculate end-to-end memory-access time, GPU throughput or AI response time.
Keep the complete server and module identities, support reference, operating MT/s and operating CL together when comparing offers. If the supplier states only rated MT/s and CL on a module, label the quotient as a specification-based calculation. Leave the actual operating comparison unresolved until the corresponding pair is supplied; a lower operating rate cannot simply be combined with the original CL by assumption.
For CL-52, a useful supplier clarification would retain both supported operating pairs and explain any differences in the complete offered configurations. If the purchase requires an application improvement, request comparison evidence for that application on those configurations. The 0.238 ns component difference cannot fill that evidence gap.
The related DDR5 channel-population guide handles channels and DIMMs per channel. The MRDIMM guide handles rank multiplexing and platform interface rates. Keep those distinct support and bandwidth questions alongside this timing comparison instead of substituting one number for another.
Carry the selected system into the physical project
After the customer and platform owner select supported equipment, Leviathan's Rack Assembly & Preparation service is a route to discuss separately agreed receiving, equipment preparation and physical rack assembly. Carry the selected server configuration, supplied equipment state and permitted remaining physical tasks into that discussion.
Use the related project inquiry with a nonconfidential equipment brief, proposed location, receiving arrangements and required handoff records. Memory qualification and application-performance acceptance remain with the appointed platform owner; the inquiry defines the physical package around the selected equipment.
Primary sources
- [CL1] Kingston KSM56R46BS8-16MH Memory Module Specifications — Rev. A, May 26, 2026Checked 2026-10-20. Document 4812048A pairs DDR5-5600 with CL46 and labels CL in cycles. This module specification illustrates notation; complete-server compatibility and actual operating timing require configuration-specific evidence.
- [CL2] Kingston DDR5 Memory Standard introduction — US MKF-954, copyright 2022Checked 2026-10-20. Page 3 defines MT/s and describes transfers on both clock edges. The two-edge relationship supports the conversion; the historical roadmap is not a current platform limit.
- [CL3] Kingston: What is CAS latency? CL and RAM timings explained — October 2025Checked 2026-10-20. Consumer explanation of CL cycles and CL × 2000 / MT/s. The quotient is used only for the CAS-derived component; consumer performance and configuration advice are outside this comparison.