I ran CrystalDiskMark on my SATA 3 connected Samsung Evo 850 SSD, and it reported a 1839MB/s sequential read speed, and 1676MB/s write speed. SATA 3 has a maximum of 750MB/s and Samsung says at best it would perform at 540MB/s. Is the software wrong, why is it so fast?enter image description here

  • Something is not right there. I am curious if the Seq is supposed to be in bits not Bytes. Still, at that you would be in the 200s – Tim Dec 31 '15 at 20:25
  • @Tim I would also be curious if any ram caching is being measured if it is not bits / bytes translation. – user493784 Dec 31 '15 at 20:26
  • It is best to use a Samsung SSD tool to determine the performance of a Samsung SSD. I honestly wouldn't trust CDM. – Ramhound Dec 31 '15 at 20:27
  • @iancnorden ram does seem more likely. – Tim Dec 31 '15 at 20:47

Apparently some of the Samsung SSD use a technology called RAPID mode. As far as I can tell this is basically a huge cache using the PC's memory. The effect you see from this in benchmarking is a dominance of memory transfer speed over SATA transfer speed especially on sequential (and therefor predictable) operations.


  • The Samsung Magician benchmark had similar results. I also checked the RAM usage as the benchmark was running, and it increased at the same time as I started the benchmark, confirming what you said. – Matthew Dec 31 '15 at 21:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.