3D XPoint Refresher

Intel's 3D XPoint memory technology is fundamentally very different from NAND flash. Intel has not clarified any more low-level details since their initial joint announcement with Micron of this technology, so our analysis from 2015 is still largely relevant. The industry consensus is that 3D XPoint is something along the lines of a phase change memory or conductive bridging resistive RAM, but we won't know for sure until third parties put 3D XPoint memory under an electron microscope.

Even without knowing the precise details, the high-level structure of 3D XPoint confers some significant advantages and disadvantages relative to NAND flash or DRAM. 3D XPoint can be read or written at the bit or word level, which greatly simplifies random access and wear leveling as compared to the multi-kB pages that NAND flash uses for read or program operations and the multi-MB blocks used for erase operations. Where DRAM requires a transistor for each memory cell, 3D XPoint isolates cells from each other by stacking them each in series with a diode-like selector. This frees up 3D XPoint to use a multi-layer structure, though not one that is as easy to manufacture as 3D NAND flash. This initial iteration of 3D XPoint uses just two layers and provides a per-die capacity of 128Gb, a step or two behind NAND flash but far ahead of the density of DRAM. 3D XPoint is currently storing just one bit per memory cell while today's NAND flash is mostly storing two or three bits per cell. Intel has indicated that the technology they are using, with sufficient R&D, can support more bits per cell to help raise density.

The general idea of a resistive memory cell paired with a selector and built at the intersections of word and bit lines is not unique to 3D XPoint memory. The term "crosspoint" has been used to describe several memory technologies with similar high-level architectures but different implementation details. As one Intel employee has explained, it is relatively easy to discover a material that exhibits hysteresis and thus has the potential to be used as a memory cell. The hard part is desiging a memory cell and selector that are fast, durable, and manufacturable at scale. The greatest value in Intel's 3D XPoint technology is not the high-level design but the specific materials and manufacturing methods that make it a practical invention. It has been noted by some analysts that the turning point for technologies such as 3D XPoint may very well be in the development in the selector itself, which is believed to be a Schottky diode or an ovonic selector.

In addition to the advantages that any resistive memory built on a crosspoint array can expect, Intel's 3D XPoint memory is supposed to offer substantially higher write endurance than NAND flash, and much lower read and write times. Intel has only quantified the low-level performance of 3D XPoint memory with rough order of magnitude comparisons against DRAM and NAND flash in general, so this test of the Optane SSD DC P4800X is the first chance to get some precise data. Unfortunately, we're only indirectly observing the capabilities of 3D XPoint, because the Optane SSD is still a PCIe SSD with a controller translating the block-oriented NVMe protocol and providing wear leveling.

The only other Optane product Intel has announced so far is another PCIe SSD, but on an entirely different scale: the Optane Memory product for consumers uses just one or two 3D XPoint chips and is intended to serve as a 32GB cache device accelerating access to a mechanical hard drive or slower SATA SSD. Next year Intel will start talking about putting 3D XPoint on DIMMs, and by then if not sooner we should have more low-level information about 3D XPoint technology.

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  • masouth - Tuesday, May 2, 2017 - link

    With ddriver and RAM? I've only skimmed ddriver's posts but I believe a summary would be.

    1) RAM is faster than this product so adding more RAM would be a better option than adding a middle man that is only faster than the data storage device but still slower than RAM.
    2) RAM has much more endurance than these drives
    3) Servers tend to stay on 24/7 and have back up power solutions (UPS, generators, etc) to allow for a RAM data flush to a non-volatile data storage device prior to any power loss so it renders Optane's advantage of being non-volatile fairly moot.

    ddriver believes these reasons result in this product having very niche uses yet Intel keeps hyping this as a solution for every user while hiding behind synthetic benchmarks instead of demonstrating real world applications which would reveal that more RAM would lead to a superior solution in many/most cases.

    I may have missed something but I think that sums up what I have read so far.
    Reply
  • masouth - Tuesday, May 2, 2017 - link

    oops, in the last part I forgot that he saying they are using the benchmarks to hide the fact that it's not as far ahead of NAND speads (although it is ahead) as they claim. Reply
  • AnTech - Saturday, April 29, 2017 - link

    Is Intel XPoint Optane a fiasco? Check out:
    Intel crosses an unacceptable ethical line
    http://semiaccurate.com/2017/03/27/intel-crosses-u...
    Reply
  • Santoval - Tuesday, June 6, 2017 - link

    A few days ago I registered here on Anandtech and I found it very odd that such a very knowledgeable website provided (only) unsecure cleartext registration and log-in forms. I felt awkward and uncomfortable, because that is a very no no for me. I wanted to register though, so I used the Tor Browser, to risk being sniffed only by the exit node. Now I see that Charlie (which I used to read ages ago) has taken this quite a few steps further..
    The guy sells $1,000 annual "professional subscriptions" on a completely private, crystal clear transparent, as public as it gets, 100% unencrypted page. I am utterly dumbfounded... And I lost all appetite to read his article or anything from him ever again. For life. Click your link and then click the "Become a subscriber" link on the top to enjoy this adorable (in)security atrocity..
    Reply
  • tsk2k - Thursday, April 20, 2017 - link

    You forgot one thing, CRYSIS 3 FPS?!?! Reply
  • philehidiot - Thursday, April 20, 2017 - link

    I find the go faster stripes on my monitor screen make a massive difference to my FPS. I have many, many more FPS as a result. It's due to the quality of the paint - Dulux one-coat just bring down my latency to the point whe...

    .... I've sniffed too much of this paint, haven't I?
    Reply
  • ddriver - Friday, April 21, 2017 - link

    If you use this instead of ram it will most likely be 3 FPS indeed :) Reply
  • mtroute - Friday, April 21, 2017 - link

    never has Intel claimed that this product is faster the DRAM...Your indignation is not proportional to even your perceived slight by Intel. You work for SK Hynix or more likely Powerchip don't you? Reply
  • ddriver - Sunday, April 23, 2017 - link

    Nope, I am self employed. I never accused intel of lying about hypetane being faster than dram. I accused them of lying how much faster than NAND it is and how close to dram it is. And I have only noted that it is hundreds of times slower than dram, making the population of dimm slots (which some intel cheerleaders claim will magically make hypetane faster) is a very bad prospect in 99.99% of the use cases.

    I don't have corporate preferences either, IMO all corporations are intrinsically full of crap, yet the amount of it varies. I also do realize that "nicer" companies are only nicer because they are it a tough situation and cannot afford to not be nice.

    What annoys me is that legally speaking, false advertising is a crime, yet everyone is doing it, because it has so many loopholes, and what's worse, the suckers line up to cheer at those lies.
    Reply
  • MobiusPizza - Sunday, April 23, 2017 - link

    It is still a first gen product and I think it has potential in servers and scientific computing. First gen SSDs were also crappy with low capacity. Give it 5 years I think it will make more sense. Reply

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