Why does DDR4 RAM have "loose" timings compared to DDR3?

[yoadknux]

Just wondering out of curiosity, when comparing DDR3 vs DDR4 at same frequency, with DDR3 it is common to see CL9/10/11 for 2133/2400MHz memory, but with DDR4 it's usually CL14/15. I suspect it's because of lower stick voltage and probably memory controller too? It's interesting that for example 6700k that supports both DDR3 and DDR4 ram can only use low profile DDR3 RAM, so it's usually low bandwidth RAM at about 1600MHz. On the other hand the 4790k can with overclock and a good motherboard do 2666MHz-2800MHz DDR3.

So really, other than the fact that new chipsets and processors support it, what advantages does DDR4 have over DDR3?

 

[EarthDog]

This may help?

https://www.howtogeek.com/238990/whats-the-difference-between-ddr3-and-ddr4-ram/
https://www.anandtech.com/show/8959...to-3200-with-gskill-corsair-adata-and-crucial

 

[mackerel]

If you think DDR4 is "bad" compared to DDR3, you're not going to like DDR5 either More speed, more latency clocks. It'll probably balance out. I can't get enough bandwidth fast enough, to hell with latency.

 

[UltraTaco]

But if you access bunch of small random stuff, don't you get penalized with higher latency? Unless it's something in the same row and you can get burst transfer? I don't know what I talking about.

 

[mackerel]

It depends on use cases. Some things respond better to latency, some to bandwidth (where latency can be hidden).

 

[Johan45]

But if you access bunch of small random stuff, don't you get penalized with higher latency? Unless it's something in the same row and you can get burst transfer? I don't know what I talking about.

If Taco is bored Taco can read this http://archive.arstechnica.com/paedia/b/bandwidth-latency/bandwidth-latency-1.html

 

[wingman99]

But if you access bunch of small random stuff, don't you get penalized with higher latency? Unless it's something in the same row and you can get burst transfer? I don't know what I talking about.

You are very close.

CAS latency Effect on memory access speed.
Because memory modules have multiple internal banks, and data can be output from one during access latency for another, the output pins can be kept 100% busy regardless of the CAS latency through pipelining; the maximum attainable bandwidth is determined solely by the clock speed. Unfortunately, this maximum bandwidth can only be attained if the address of the data to be read is known long enough in advance; if the address of the data being accessed is not predictable, pipeline stalls can occur, resulting in a loss of bandwidth. For a completely unknown memory access (AKA Random access), the relevant latency is the time to close any open row, plus the time to open the desired row, followed by the CAS latency to read data from it. Due to spatial locality, however, it is common to access several words in the same row. In this case, the CAS latency alone determines the elapsed time. https://en.wikipedia.org/wiki/CAS_latency

 

[UltraTaco]

Ok, so I read Johan's article. Very good read! I appreciate how much work is going into getting my data through the bus. Makes me want to overclock it even harder now! More speed!

Mr.Wingman Sir, thank you for wiki article as well.

 

[Alaric]

In all fairness, for the things she does (email, FB, web surfing) my girlfriend's FX with 16 GB of DDR3 1866 MHz is every bit as fast as my rig. Web pages load fast, calculator works in zippy fashion, etc.. Unless I look for things to do faster than her rig it's all good. We've been in the incremental stages of improvement for years now, except in specialized cases. Those cases would be most of the folks who responded here. Hardware has improved immensely, but usage is pretty static. In my case internet speed is a limiting factor. LOL A good SSD and best practices for OS maintenance and tuning will generally make the differences between DDR3 and DDR4 pointless for the majority of uses.

 

[Woomack]

In short:
- DDR4 has a higher internal bandwidth
- higher frequency = lower latency + higher mem bandwidth, tighter timings = almost only lower latency
- latency highly depends on CPU-RAM-Cache connection speed, new CPUs have mostly improved cache speed and internal access time what with new instructions give higher IPC performance what we see
- higher frequency = higher bandwidth, new platforms are highly multithreaded so bandwidth affects performance more than lower latency (also because latency in big part is covered by cpu-cache speed)

Other theoretical advantages of DDR4:
- lower voltage, lower power, lower heat
- higher capacity

this was already posted couple of times:
http://www.crucial.com/usa/en/memory-performance-speed-latency

Here is also my early DDR3 vs DDR4 comparison at the same frequency and main timings (different platforms but IPC not much different)
https://www.overclockers.com/forums/showthread.php/750439-DDR3-4930K-vs-DDR4-5820K-comparison