4 ms·
Is there a "rule of thumb" to estimate speeds vs DDR4? The "7200" implies it will 2x as fast as DDR4-3600. But what about latency? It seems like latency has
by drewg123 5y ago
Is there a "rule of thumb" to estimate speeds vs DDR4? The "7200" implies it will 2x as fast as DDR4-3600. But what about latency? It seems like latency has not been improving along with bandwidth..
- theandrewbailey 5y agoI made a spreadsheet that calculates RAM speeds and CAS timings into nanoseconds: https://docs.google.com/spreadsheets/d/1fFg2YwccdeCU5lFZ1vild-y9g9k9he966QC_jXAbbJU/edit#gid=1654750461 https://docs.google.com/spreadsheets/d/1fFg2YwccdeCU5lFZ1vil... I've noticed that popular speeds and timings across RAM generations have tended to keep roughly similar 9-10ns latency. Going by that, DDR5-7200 kits should have CAS timings around 32-36.
- mweberxyz 5y agoLatency will remain around the same levels as DDR4. The increase in clock speed will yield a hypothetical increase in maximum bandwidth. (via https://www.anandtech.com/show/16143/insights-into-ddr5-subtimings-and-latencies https://www.anandtech.com/show/16143/insights-into-ddr5-subt...)
- shadilay 5y agoWhen Mhz increases the CAS latency also increases.
- theandrewbailey 5y agoCAS latency, as measured in cycles, goes up, but since each individual cycle is shorter, it ends up being the same in actual time.
- shadilay 5y agoYeah, DRAM latency improvement stalled out something like 10 years ago. At least we're getting on package HBM and SRAM now.
- ksec 5y ago>But what about latency? From a high level overview DRAM latency has been the same and will stay the same for long time. Doubling the bandwidth, lower energy usage, double capacity all while staying with the same latency is about as good as it get for DRAM. You will need eDRAM to get lower latency. That is why we see the trend of an increase of cache size on CPU.