DDR4 vs GDDR5 - How close?

[Yeroon]

Question for you memory experts - How close to gddr5 will ddr4 get in terms of bandwidth and latency? Will it be able to fix the gap for integrated gpu's memory limitations when it becomes available?
I'm having trouble finding out exactly what makes ddr3 based gddr5 much different from ddr4, and why gpu memory clocks go from being something like 1500 core, 6000 effective memory clocks?
If theres links to some good articles that I managed to miss about either type, post em up if you'd be so kind.

Yeroon

[zanzabar]

gddr3 and 4 are basically the same thing, 4 is lower voltage and high clocked by a little but they are the same kind of thing. gddr5 is actually qdr (4x speed for effective rate instead of 2) and is much quicker than 3 or 4. one of the things you have to look out for is nvidia based cards that get rated with gddr5 as ddr and giving the non effective clock speed of half the effective, this is wrong be on the look out for it if it seems to fast in the specs.

so if you have 1ghz 3 or 4 on a 128bit buss that gives you 34GB/s, but with 1ghz gddr5 it gives you 68GB/s. [(1ghz)(1024/1000)^3(128bit/8)(data rate)] the data rate is 2 for ddr and 4 for qdr (like gddr5 or rambus stuff)

[Yeroon]

Thanks, didn't know about qdr. But, if its qdr why is it listed as gddr?
Also, with ddr4 being point to point memory over the multi-drop bus of ddr3, does this affect bandwidth?
Yeroon

[zanzabar]

Thanks, didn't know about qdr. But, if its qdr why is it listed as gddr?
Also, with ddr4 being point to point memory over the multi-drop bus of ddr3, does this affect bandwidth?
Yeroon

gddr5 kept its name based on being part of the gddr family.

for the actual electronics when comparing 3 and 4, nvidia only uses ddr3 and gddr3, and amd uses ddr3 so i do not think that it matters anymore since it all moved to gddr5 or regular ddr3.