Re:Samsung Reveals DDR5-7200 512GB RAM
by drewg123 on Tuesday August 24, 2021 @11:03AM
(#28289762)
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..
[ Parent
| on HN ]
Latency 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-subt...)
Re:Samsung Reveals DDR5-7200 512GB RAM
by theandrewbailey on Tuesday August 24, 2021 @04:58PM
(#28294933)
I made a spreadsheet that calculates RAM speeds and CAS timings into nanoseconds: 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.
>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.
When Mhz increases the CAS latency also increases.
Re:Samsung Reveals DDR5-7200 512GB RAM
by theandrewbailey on Tuesday August 24, 2021 @01:48PM
(#28292456)
CAS latency, as measured in cycles, goes up, but since each individual cycle is shorter, it ends up being the same in actual time.