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DDR3 vs. DDR4: Raw bandwidth by the numbers

By Jos
Sep 17, 2015
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  1. We’ve been collecting data on memory bandwidth for some time now – of course we have – but one of the big questions hanging over Skylake is what the DDR4 support really brings to the table. It’s also worth comparing four generations of memory controllers – two dual-channel and two quad-channel – and seeing what the weaknesses and strengths of each one are.

    Editor's note: Guest author Dustin Sklavos is a Technical Marketing Specialist at Corsair and has been writing in the industry since 2005. This article was originally published on the Corsair blog.

    With all that in mind, we compared Intel’s Ivy Bridge-E (quad-channel DDR3), Haswell (dual-channel DDR3), Haswell-E (quad-channel DDR4), and Skylake (dual-channel DDR4) at a variety of speed grades in synthetic testing in AIDA64 to isolate raw memory bandwidth. You may have heard by now that Skylake has a very robust memory controller, and that’s turned out to be true as you’ll see.

    The following CAS latencies were used for each speed grade:

    Memory clock DDR3 CAS latency DDR4 CAS latency
    1600 MHz 10
    1866 MHz 11
    2133 MHz 11 15
    2400 MHz 11 15
    2666 MHz 11 15
    2800 MHz 12 16
    3000 MHz 16
    3200 MHz 16
    3333 MHz 16
    3466 MHz 18
    3600 MHz 18

    One crucial thing to point out with DDR4 is that it has an oddball “CAS latency hole.” You’ll notice we jumped directly from C16 to C18; C17 isn’t officially supported. The result is that there is a substantial jump in CAS latency moving up to 3466MHz that needs to be ameliorated, amusingly enough, by driving the memory at even higher clocks.

    Read speed

    The blue bars represent our DDR3 configurations, while the red bars represent our DDR4 configurations. This should hopefully lay to rest some concerns about DDR4’s higher latencies negatively impacting performance when compared to DDR3. There were situations where DDR3 could be faster than DDR2 during that transition, but DDR4 is a different animal. It offers consistently higher read bandwidth at the same clock.

    Note also that Haswell’s memory controller has a hard time going past 2400MHz, which really has been the performance sweet spot in DDR3. Yet there’s no point where the wheels start to shake on Skylake’s controller; it continues scaling, even up to and beyond 3600MHz.

    Finally, one more trend you’ll see: DDR4-3000 on Skylake produces more raw memory bandwidth than Ivy Bridge-E’s default DDR3-1600. We now have a mainstream, dual-channel platform capable of generating nearly as much memory bandwidth as last generation’s quad-channel.

    Write speed

    Interestingly, it seems like memory write operations have consistently been a minor sore spot. Haswell-E’s memory write performance capped at ~48000 MB/s and basically stayed there regardless of speed. That’s mighty fast, but Skylake is able to actually exceed it at 3200MHz and beyond. Skylake also easily eclipses Haswell and Ivy Bridge-E.

    Copy speed

    The memory copy operations look basically the same as the read operations. Haswell has the same drop at 2666MHz, and the DDR4-equipped platforms are consistently faster even at the same speed. Skylake’s exceptional ability to scale up in clock speed allows it to make up bandwidth and, at a high enough speed, put it in striking distance of Haswell-E.

    Latency

    This is arguably what DDR4 skeptics are going to gravitate toward despite the immense raw bandwidth of the technology. DDR4 latency is a bit higher than DDR3, but not catastrophically so.

    What you need to focus on is essentially mapping the curve of DDR3 against the curve of DDR4. DDR3 more or less starts at 1600MHz for mainstream platforms, while DDR4 doesn’t go below 2133MHz. So at the entry level for each platform, latency is more or less the same, while bandwidth is significantly better on DDR4.

    Conclusions

    First, while Skylake’s instructions-per-clock gains are a little underwhelming, its memory controller is something else entirely. We’ll need to see how it handles DDR3L – and we’ll be testing that in greater detail soon enough – but it has none of the scaling hiccups any of its predecessors have. Skylake’s memory controller is incredibly robust, and Skylake seems to overall be more efficient with memory in general.

    Second, DDR4 just doesn’t have the latency issues the transition from DDR2 to DDR3 did. In fact, it’s only when you’re making the C16 to C18 jump that overall latency starts to creep up, but that’s solved almost immediately by just going to the next speed grade.

    Ultimately, DDR4 draws less power, runs cooler, and delivers more bandwidth-per-clock than the venerable DDR3, and it has the scaling headroom that DDR3 lacked in both capacity and raw bandwidth. In other words, it’s a worthy successor.

    Header image credit: Icon Craft Studio / Shutterstock

    Permalink to story.

     
  2. Skidmarksdeluxe

    Skidmarksdeluxe TS Evangelist Posts: 6,513   +2,056

    It'll be a while before I step up to DDR4, by then things will have got even better.
     
  3. kuroiei

    kuroiei TS Enthusiast Posts: 93   +31

    None of my machines are even DDR3 yet! Changing all the guts just for RAM is a bit pricey where I live... :/
     
    SantistaUSA and Arris like this.
  4. robb213

    robb213 TS Addict Posts: 315   +93

    It's not like you'll get much of a performance boost from the RAM alone anyways, unless you're encoding/rendering/producing with certain software. It's just a new technology, so everyone has to have it.

    Still, the CPU and GPU that matter the most...something most of my *****ic friends have completely forgotten.
     
    SantistaUSA and Evernessince like this.
  5. Evernessince

    Evernessince TS Evangelist Posts: 1,199   +593

    Yep. Has everyone noticed all the efforts to side-step the CPU? GPUs are outpacing CPUs so badly nowadays more and more software relies on GPU power instead of CPU, which has remained largely the same for the last 5 years.
     
    madboyv1 likes this.
  6. EEatGDL

    EEatGDL TS Maniac Posts: 481   +159

    It was all synthetic, I want to see real world scenarios. It's like in the CPU's benchmarks: Intel chips always have the best memory bandwidth performance but when gaming the mileage varies. If I'm spending a lot of money in going from DDR3 to DDR4 for mostly gaming, I want to see a real benefit.
     
  7. kuroiei

    kuroiei TS Enthusiast Posts: 93   +31

    Yup. Rendering, to be exact. Demanding as much CPU power, core count and RAM amount I can afford. I'm all for new technology, but looking realistically - I don't need the latest stuff to get the job done. My current tech just shows its age, and the fast pace new components are released can get one's head spinning in no time. :)
     
  8. treetops

    treetops TS Evangelist Posts: 1,953   +162

    I had no clue my 4x 2gig dd3 was suffering so much :( from quad channel
     
  9. Petr Bendak

    Petr Bendak TS Rookie

    Crysis 3 fps gains????
     
  10. Negative 287

    Negative 287 TS Rookie

    This is only half the argument!

    I want to see what DDR3 2.4 GHz Quad Channel RAM does compared to the DDR4 Quad Channel at the same speed.
     
  11. Justinus

    Justinus TS Rookie

    I call bull$$$$ on the haswell-e testing. It reeks of they-didn't-do-it-right.

    I downloaded the latest AIDA64 extreme and tested my own haswell-e rig. I've got quad channel DDR4 3000 at CL15, and I got these results (Each result is the average of 3 tests). Compare these to the chart, and you can see the chart is crap.

    Read: 70,311
    Write: 67,714
    Copy: 68,488
    Latency: 53.8

    Compared to the charts:
    Read: ~60,500
    Write: ~48,000
    Copy: ~64,500
    Latency: ~62

    The latency difference is most definitely my tighter timings, but there's no way you can account for a 10,000 mb/s read difference, 19,000 mb/s write difference with the CL being 15 instead of 16.

    Please, don't draw conclusions from clearly erroneous testing. Haswell-e is definitely competitive with previous quad channel platforms and definitely competitive relative to Skylake.
     

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