From DDR3 to DDR4: Bandwidth by the Numbers

By Dustin Sklavos, on September 15, 2014 08:25 PM

We’ve done a couple FAQs and Q&As, but we haven’t painted a clear, by-the-numbers picture yet of what DDR4 really has to offer beyond DDR3. On the desktop side the lower power consumption is offset somewhat by the fact that the only platform that supports it starts chugging power the instant overclocking gets involved, while 16GB DIMMs (one of the key advantages of DDR4) aren’t expected to be available until 2015.

That leaves us with performance. A lot of users are concerned that the increased timings on DDR4 make it inferior to DDR3 at similar speeds, but that doesn’t really tell the whole story. While DDR2 and DDR3 were architecturally very similar and took some time to separate, DDR4 is host to a few internal architectural changes that affect overall latency and performance. Those changes allow it to see benefits over DDR3 right out of the gate.

I want to stress that this exercise, at least right now, is academic: there is no platform currently available that supports both DDR3 and DDR4. So if you want DDR4, you’re using Haswell-E, and vice versa. That makes this comparison a little bit difficult since it’s tough to quantify in apples-to-apples terms whether or not DDR4 really is “faster” than DDR3.

For testing, I used three platforms with both single rank and dual rank DIMMs. Dual rank DIMMs increase parallelization a little bit at the cost of a very minor hit in latency, typically about 1ns. In lay terms, denser memory DIMMs (i.e. 8GB) get a little more mileage than lower capacity, single rank DIMMs (i.e. 4GB). Single rank DIMMs pretty much have to bank on hitting higher speeds to make up the deficit.

These are the testbeds I used:

	Haswell	Ivy Bridge-E	Haswell-E
CPU	Intel Core i7-4790K	Intel Core i7-4930K	Intel Core i7-5960X
Motherboard	ASUS Z97-WS	ASUS P9X79 Pro	ASUS X99-Deluxe
Single Rank Kit	CMY16GX3M4A3000C12R	CMD16GX3M4A2933C12	CMD16GX4M4B3200C16
Dual Rank Kit	CMY32GX3M4A2800C12R	CMY64GX3M8A2400C11R	CMD32GX4M4A2800C16
Memory Channels	2x DDR3	4x DDR3	4x DDR4

Note that in each case, the CPU’s core clock was set to 4GHz and uncore clock was set to 3GHz.

And these are the latencies I tested with at each speed:

	DDR3	DDR4
1600 MHz	10-10-10-30
1866 MHz	11-13-13-31
2133 MHz	11-13-13-31	15-15-15-35
2400 MHz	11-13-13-31	15-15-15-35
2666 MHz	11-13-13-31	15-15-15-35
2800 MHz	12-14-14-36	16-16-16-36
3000 MHz		16-16-16-36
3200 MHz		16-16-16-36

You can see I’ve tried to make it as apples-to-apples as possible, but these are different architectures and memory controllers. For bandwidth testing, I used AIDA64.

I’m keen to point out before we get started that it’s tough to actually quantify “faster” since there are essentially four disciplines you’re looking at: three that are bandwidth related and one that is latency related. It’s more sensible to look for trends.

READ	1600	1866	2133	2400	2666	2800	3000	3200
Haswell 1R	23233	26392	30586	34079	22850	23917
Haswell 2R	23982	27840	31833	*35406*	23585
Ivy-E 1R	41435	48444	50573	55197
Ivy-E 2R	43670	50520	57341	*59831*
Haswell-E 1R			54514	57664	60025	59651	60848	*62407*
Haswell-E 2R			56771	60231	62164	61045

So right off the bat, you can see Haswell’s dual-channel memory controller is going to have a hard time keeping up with the quad-channel memory controllers on Ivy Bridge-E and Haswell-E. What’s notable right off the bat, though, is that DDR3 and DDR4 are very close at the same clock speed despite DDR4’s increased CAS latency. In fact, if you’re using single rank DIMMs, DDR4 is measurably faster than DDR3.

You may also be seeing Haswell’s memory bandwidth take a bath after 2400MHz; this is something independently verifiable. Latency continues to improve past 2400MHz, but memory bandwidth takes a consistent hit. Meanwhile, Haswell-E’s DDR4 controller takes a slight dip at 2800MHz when we have to shift to CAS16 from CAS15, but resumes climbing at 3000MHz and 3200MHz.

WRITE	1600	1866	2133	2400	2666	2800	3000	3200
Haswell 1R	23715	27157	30852	34819	22926	24053
Haswell 2R	25132	29222	33248	*37415*	24158
Ivy-E 1R	30537	33096	37845	42184
Ivy-E 2R	31488	52746	*60432*	43347
Haswell-E 1R			46711	46817	46919	46888	46927	47009
Haswell-E 2R			47758	47832	47892	*47912*

At this point it’s obvious Intel’s Ivy Bridge-E and Haswell DDR3 controllers just weren’t architected to handle high speeds. Ivy Bridge-E and DDR3 do offer consistently higher write speeds than DDR4 does (provided you’re running dual rank modules), while DDR4’s write speed is essentially constant and stable at about 47GB/s.

While write speeds are obviously a weak point in Haswell-E’s DDR4 memory controller, they’re really the only one.

COPY	1600	1866	2133	2400	2666	2800	3000	3200
Haswell 1R	21557	24347	27535	30596	22256	23324
Haswell 2R	23794	27262	30494	*33635*	23557
Ivy-E 1R	39492	44368	49485	54149
Ivy-E 2R	43876	51026	58393	*59667*
Haswell-E 1R			52447	57749	62076	62793	65558	*68990*
Haswell-E 2R			56066	61703	67144	59848

Memory copy functions start slightly behind DDR3 at 2133MHz and then pretty much start soaring past it at 2400MHz. Judging from the synthetics so far, it seems like users who want to start getting the most out of Haswell-E should be looking at 2666MHz kits at a minimum. Again, mainstream Haswell’s dual-channel DDR3 controller is totally outclassed by the fatter pipes of these higher end, hexa-core and octal-core processors.

COPY	1600	1866	2133	2400	2666	2800	3000	3200
Haswell 1R	60.2	57.2	53.6	48.6	46.1	*45.6*
Haswell 2R	61.5	58.3	53.7	49.4	46.5
Ivy-E 1R	78.3	72.2	65.7	60.6
Ivy-E 2R	80.8	67.7	*60.1*	61.7
Haswell-E 1R			71.3	66.2	62.3	63.3	61.2	*56.3*
Haswell-E 2R			72.9	67.5	63.3	64.6

This is probably the biggest bugbear in the transition from DDR3 to DDR4. But users expecting DDR4 to grossly underperform DDR3 due to the higher CAS latency are going to be in for a surprise: as you ramp DDR4 to its intended speeds, latency actually drops below DDR3 (excepting Haswell’s dual-channel controller, which is just plain lower latency than both quad-channel controllers.) So while it’s true that DDR4 can be as much as 10ms slower than DDR3 at the same clock speed, it still has lower latency at its mainstream speeds, and the deficit isn’t any greater than if you were going from Haswell’s dual-channel controller to Ivy Bridge-E’s quad-channel.

Ultimately that’s kind of the takeaway here: DDR4 starts at very high speeds with room to scale higher, and at those entry level speeds, it’s faster and more capable than its predecessor in almost every test. Mainstream DDR4 actually winds up with lower overall latency and higher bandwidth than mainstream DDR3. In the future we’ll be testing DDR4 in practical applications to see if there are performance gains to be had from exceeding the baseline 2133MHz, but for now it’s clear that if nothing else, DDR4 is a more than worthy successor to DDR3, and fears regarding the higher timings resulting in substantially increased overall latency are by and large unfounded.

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Comments

Arne said:
2/26/2017 11:00 AM

Honestly these AIDA64 numbers look quite phony. Why not use an open source bandwidth measuring tool so you know the numbers are valid?
Me said:
12/28/2015 4:18 AM

A good amount of fairly in-depth tests that have certainly helped me have a more clear idea of the on-paper advantages of DDR4 against DDR3. If only, there is one test that I would be utterly grateful if you could do in any future posts - Try loading a RAM intensive software on both sets and count the actual loading time.
Carmazin Corsair said:
8/11/2015 9:23 PM

Hat about Mobile Intel's 6th Generation Skylake Xeon Core i7-6700K 2133 MHz (4 x 16)? For the new LENOVO P70? We need a better PRCE on it
Cereal Keller said:
7/11/2015 12:42 AM

I have a 4790k, which is Devils Canyon btw, and I'm running 2666 MHz set of DDR3 RAM 2x8 GB 11-13-13-35 1T on my AS Rock Z97 OC Formula. I'm not using Corsair RAM. But, I'm seeing read and writes at 40 GB/sec. Which it pretty much linear for what you would expect to see on your graphs. I don't understand why the speeds take a massive dive after 2400 MHz, because mine don't.
kira said:
3/28/2015 1:04 AM

there are no difference between the two of them beside the CAS lentancy for only 10ms to 10ns it still depends on how to consumers will use the DDR3 and DDR4 if its more in video editing performance i really recommend that you use DDR4 for this but if you are an average gamer try to only use DDR3 for more than DDR4 since the main difference is on CAS lentancy geez this is not a big different as of know but i the near future this will be nice to have more the twice the data usage on DDR4 :))))
Sandy Marshall said:
1/13/2015 5:20 AM

To Whom It May Concern .... How about displaying the voltage they run at Stock and what can they be overclocked to ???? Geeezzzzeeee , Nowhere , nothing about voltage specs. All the memory in your online store or stores should have those specs included also .. Mr. Marshall Please reply to.. Cool711@Alaskan.net
Sandy Marshall said:
1/13/2015 5:19 AM

To Whom It May Concern .... How about displaying the voltage they run at Stock and what can they be overclocked to ???? Geeezzzzeeee , Nowhere , nothing about voltage specs. All the memory in your online store or stores should have those specs included also .. Mr. Marshall Please reply to.. Cool711@Alaskan.net
Sandy Marshall said:
1/13/2015 5:18 AM

To Whom It May Concern .... How about displaying the voltage they run at Stock and what can they be overclocked to ???? Geeezzzzeeee , Nowhere , nothing about voltage specs. All the memory in your online store or stores should have those specs included also .. Mr. Marshall Please reply to.. Cool711@Alaskan.net
Sandy Marshall said:
1/13/2015 5:17 AM

To Whom It May Concern .... How about displaying the voltage they run at Stock and what can they be overclocked to ???? Geeezzzzeeee , Nowhere , nothing about voltage specs. All the memory in your online store or stores should have those specs included also .. Mr. Marshall Please reply to.. Cool711@Alaskan.net
Sandy Marshall said:
1/13/2015 5:16 AM

To Whom It May Concern .... How about displaying the voltage they run at Stock and what can they be overclocked to ???? Geeezzzzeeee , Nowhere , nothing about voltage specs. All the memory in your online store or stores should have those specs included also .. Mr. Marshall Please reply to.. Cool711@Alaskan.net
Sandy Marshall said:
1/13/2015 5:15 AM

To Whom It May Concern .... How about displaying the voltage they run at Stock and what can they be overclocked to ???? Geeezzzzeeee , Nowhere , nothing about voltage specs. All the memory in your online store or stores should have those specs included also .. Mr. Marshall Please reply to.. Cool711@Alaskan.net
bjone said:
10/20/2014 10:23 AM

So while it’s true that DDR4 can be as much as 10ms slower than DDR3 at the same clock speed. Typo: 10ns Did I won some DDR4 kit :D ?
Fredrik Borsheim said:
9/17/2014 12:38 AM

Awsome clearup on the confusion of ddr4 cas latency beeing "too damn high" Thank you for this :)