DDR4 is no better than DDR3

[Akhil Shekar]

Hi,

 

So I was doing some research on memory layouts for a graduate project and was reading some papers on it. I came across this interesting research article from Carnegie Mellon University published and accepted in a reputable and prestigious computer architecture journal.

 

If somebody wants to have a look at it, this is the link to the article : https://dl.acm.org/doi/pdf/10.1145/3366708

I think this is a more digestible presentation (ppt) version of the paper : https://people.inf.ethz.ch/omutlu/pub/Workload-DRAM-Interaction-Analysis_sigmetrics19-talk.pdf

 

The gist : DDR4 is not really much better than DDR3 in some of the workloads. In fact in certain benchmarks, it is quite regressive when compared to DDR3. The authors compared it with 9 popular memory technologies such as GDDRx, LPDDRx etc. and concluded that the LPDDR scores slightly better due to its low power usage and embedded nature.

 

When Linus keeps telling that DDR4 improves the performance, I think we really need to put this to test or atleast have a discussion or a disclaimer as to if this is credible?

 

Why? Because memory doesnt scale really well in terms of manufacturing like CPU. CPU is classified as logic and manufacturing a CPU or logic block is vastly different from manufacturing a memory block. Because transistors leak charge all the time, and when you try to cram as much capacity inside a single DIMM as possible, the latency actually increases since now the charge needs to travel longer distance to get sensed as 1 or 0.

But hey Akhil, isnt it that when transistor size decreases, the performance increases? It is true for a logic block or CPU, but for memory, it doesnt hold true because as you decrease the transistor size, the charge literally leaks much easier now. Think of transistor like a tap and capacitor holding your 1 or 0 bit as a water tank. Now when the tap is made smaller, the tank puts so much pressure on the tap that the water keeps dripping drop by drop.

This is what happens when you try to decrease transistor size in DDR memories, the charge keeps leaking. Memory companies need to come up with various ways to arrest this leakage and cut corners else where. (In electronics, the famous saying goes: you can't have free lunch).

 

Hence, thats why you dont have 7nm memories even thought CPUs are on 7nm.

 

So essentially having DDR4 doesnt really improve your speeds by that much, or atleast it is really debatable.

[Haro]

3 minutes ago, Akhil Shekar said:

When Linus keeps telling that DDR4 improves the performance

I think your mistaking ddr4 frequency and not the actual dimm it self 

 

3 minutes ago, Akhil Shekar said:

the latency actually increases

Every one knew that 

Everyone knows that trc and cl on ddr3 is much better than ddr4 

Lmao 

4 minutes ago, Akhil Shekar said:

So essentially having DDR4 doesnt really improve your speeds by that much, or atleast it is really debatable.

Do you think this is a new discovery or something?

[5x5]

Welcome to 2015

[WereCatf]

25 minutes ago, Akhil Shekar said:

So essentially having DDR4 doesnt really improve your speeds by that much, or atleast it is really debatable.

Wrong conclusion drawn from the papers, need to go back and re-read the whole thing with more effort. For example, speed, in this context, is actually two different things: bandwidth and latency. You are conflating the two things into an amorphous, unrecognizable and ultimately meaningless blob.

 

25 minutes ago, Akhil Shekar said:

concluded that the LPDDR scores slightly better due to its low power usage and embedded nature

This isn't even relevant wrt. performance in the first place.

[GenericFanboy]

This just feels like people reading 1 thing, and instantly believing the difference. DDR3 has things its better in. But ddr4 just has so many advantages. Do you really think DDR4 would be a thing if it was w o r s e than ddr3?

[Drama Lama]

DDR 4 has many advantages for example it runs on lower voltages

[WereCatf]

Poor OP: strolls in here, thinking he be cool shit and found something no one else knew, and then the LTT-forums descend on him

 

[Haro]

Just now, WereCatf said:

the LTT-forums descend on him

He got disintegrated

[LukeLinusFanFic]

When did Linus ever say that ddr4 is better than ddr3? You never had a choice, regardless?

[WereCatf]

2 minutes ago, LukeLinusFanFic said:

When did Linus ever say that ddr4 is better than ddr3? You never had a choice, regardless?

I have a faint memory of him actually saying something about the DDR3 vs. DDR4 latency some years ago. I'm not sure if I'm just imagining the memory, but it's not like Linus is new to this stuff, either.

[LukeLinusFanFic]

7 minutes ago, WereCatf said:

I have a faint memory of him actually saying something about the DDR3 vs. DDR4 latency some years ago. I'm not sure if I'm just imagining the memory, but it's not like Linus is new to this stuff, either.

I remember him talking on the wan show about his video comparing the two. He said it's basically the same deal with the jump to ddr3, and ddr2 - more latency, but greater speed and capacity

[akio123008]

Aren't we going to mention that if you want to use DDR3 you're stuck with much older mobos and cpus?

[WereCatf]

21 minutes ago, akio123008 said:

Aren't we going to mention that if you want to use DDR3 you're stuck with much older mobos and cpus?

You're not wrong, but I'd argue that's not relevant. This context is about the performance-differences between the two; what platform you use to utilize one or the other would be more relevant when talking about compatibility or systems-design or such aspects. Besides, everyone knows you can't use DDR3 in modern PCs, so is it even worth mentioning?

[KarathKasun]

Latency is slightly better at higher DDR4 frequencies, bandwidth is greatly improved.

 

Also, these charts show "IPC".  DDR4 has about the same "IPC" as DDR3, but higher clocks... SIGNIFICANTLY higher clocks.

[TheDankKoosh]

DDR4 can overcome the latency deficit by way of highly increased clock speeds, with current platforms 3600mhz is a standard high speed, similar to 2133 on later DDR3 platforms. Samsung b die brings in DDR3-like latency due to it's ability for extremely tight timings and high speed potential. For instance 2400 cl9 (fairly hard to achieve) will be around the same latency as 3600 cl14 (achievable on current platforms with little issue), but the DDR4 will have massively increased bandwidth which is fairly important when feeding modern CPUs with information. Overall DDR4 has a good advantage over DDR3 and with only half the time to mature; it can only go up from here.