Intel's roadmap for Optane SSDs with 1,000x performance

Re:Intel's roadmap for Optane SSDs with 1,000x performance by chongli on Monday June 13, 2016 @10:45PM (#11899422)

When we talk about 1ns latency for DRAM we aren't talking about access latency, we're talking about CAS latency[0]. This is how fast the DRAM actually works. It doesn't include the rest of the overhead between the time the data is sent over the bus and the time it's loaded into a register and ready for an instruction to operate on it.

CAS latency for DDR3-3300 is less than 1/3ns, according to the article below. If Intel's new Optane memory can achieve addressing on the order of 10ns, it will be very competitive with DRAM, since all of other overhead along the data path ought to be similar.

[0] https://en.wikipedia.org/wiki/CAS_latency

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Re:Intel's roadmap for Optane SSDs with 1,000x performance by vitus on Monday June 13, 2016 @11:36PM (#11899572)

This is actually slightly incorrect. You seem to be calculating as if the clock rate were 3300MHz, even though the listed number in DDR (double data rate) is actually double the actual clock rate (IIRC, for marketing reasons).

On top of that, the CAS latency is given in cycles -- the cited CAS latency for DDR3-3300 is 16 cycles. Multiplying # cycles by time per cycle yields a value closer to 9-10ns. Note that this is the "first word" latency in this table.

- The other thing you may be talking about is this "bit time", which looks like it's simply inverse throughput. It's very important not to conflate throughput with latency.

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