Question Bandwidth DDR4 vs. DDR3.

[Endre]

Though DDR4 came with higher frequencies, it also came with higher CAS Latencies (CL), resulting in a pretty small improvement regarding responsiveness, over DDR3.
How is the bandwidth of DDR4 compared to DDR3? Are there any improvements? (as it is between single channel vs. dual channel; or between: PCIEX8 vs PCIEX16, etc.)

 

[thx1138v2]

How to calculate bandwidth: https://www.hardwaresecrets.com/eve...iple-and-quad-channel-memory-architectures/2/

Keep in mind that the calculated bandwidth is theoretical only. Your machine will not live up to the calculated bandwidth because the CPU doesn't transfer data on every cycle.

 

[boju]

https://www.crucial.com/usa/en/memory-performance-speed-latency

Higher frequency is better, CL timings isn't the true latency.

 

[USAFRet]

And not directly comparable, due to the other platform differences.

 

[Karadjgne]

Ddr3 2400 CL12 has the same true latency as ddr4 3200 CL16, both at 10.00ns. But that again is only part of the story since the data transfer rate of the ddr3 is only 1200MHz, whereas the ddr4 is 1600MHz, a substantial loss in speeds for the ddr3, but again that's only part of the performance since there's 40 odd secondary and tertiary timings that affect things as well as the primary 5. And that's just in the ram itself, that's not taking the memory controllers speeds, motherboard bandwidth capacity and various other changes into account.

Basically, just because they are both somewhat round and both fruit, doesn't mean apples will compare to oranges.




Even Haswell-E quad channel DDR3 bandwidth gets dusted by a skylake cpu on DDR4 in anything but copy where double the bandwidth with quad channel has a serious advantage. With CoffeeLake's faster memory controller, expect even that gap to be smaller and write bandwidth to be higher.

 

[Endre]

Ddr3 2400 CL12 has the same true latency as ddr4 3200 CL16, both at 10.00ns. But that again is only part of the story since the data transfer rate of the ddr3 is only 1200MHz, whereas the ddr4 is 1600MHz, a substantial loss in speeds for the ddr3, but again that's only part of the performance since there's 40 odd secondary and tertiary timings that affect things as well as the primary 5. And that's just in the ram itself, that's not taking the memory controllers speeds, motherboard bandwidth capacity and various other changes into account.

Basically, just because they are both somewhat round and both fruit, doesn't mean apples will compare to oranges.




Even Haswell-E quad channel DDR3 bandwidth gets dusted by a skylake cpu on DDR4 in anything but copy where double the bandwidth with quad channel has a serious advantage. With CoffeeLake's faster memory controller, expect even that gap to be smaller and write bandwidth to be higher.

So, with other words DDR4 will always outperform DDR3, even if “on paper”, by calculating the True Latency, they look pretty much at the same speed?

 

[Karadjgne]

As you see from those graphs, high speed ddr3 can pretty much keep up with lower speed ddr4, if running quad channel, since quad doubles your available bandwidth. But on dual vs dual, ddr3 pretty much gets dusted.

It's like big block vs small block motors. Can both be V8, both have equitable HP, similar cubic inches etc, but due to internal designs, cams, crank etc when it comes to low rpm torque, the small block doesn't even come close.