
Intel to Launch 3D XPoint DIMMs in 2H 2018 - p1esk
https://www.anandtech.com/show/12041/intel-to-launch-3d-xpoint-dimms-in-2h-2018
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continuations
Do these really have RAM-like performance or is Intel calling them DIMMs as a
marketing ploy?

I still remember when Optane was first announced Intel hyped it as a
replacement for RAM. When it was finally available it turned out to be about
1,000x slower than RAM and barely faster than other SSD. So much for RAM
replacement...

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fgonzag
Barely faster than NVMe SSDs when fully saturated. At low queue depths and in
mixed workloads (especially when overwriting data) Optane absolutely destroys
the competition. This is a database dream drive. Only problem is the low
capacities right now.

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AndrewDavis
It's much better in latency too[1].

I also wonder if the current products are bottlenecked by the controller and
whether DIMMs will see vastly superior performance. Guess we'll have to wait
and see.

[1][https://www.pcper.com/reviews/Storage/Intel-Optane-
Memory-32...](https://www.pcper.com/reviews/Storage/Intel-Optane-Memory-32GB-
Review-Faster-Lightning/Depth-Performance)

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wtallis
> I also wonder if the current products are bottlenecked by the controller

There's no question that they are. NVMe drive prototypes that use DRAM as
their backing memory instead of flash or some other persistent memory have
about the same overall latency as Optane SSDs.

With NVMe, the storage industry is in a much better position to take advantage
of 3D XPoint than if we were all still using SATA or SAS, but it's still on a
peripheral bus not a memory bus.

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Tepix
This could be an amazing technology for high performance mobile devices,
especially laptops.

For this first release, "3D XPoint DIMMs will require server platform support
because they are unlikely to operate as standard DDR4 DIMMs. The JEDEC
NVDIMM-P standard for persistent memory DIMMs has not been finalized and is
expected next year".

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eloff
Whether they have an $8B market or not will very much depend on the
performance and price. I really hope they can make it work though. The first
generations of a new technology are typically not much to get excited about,
but as it gets better over time this could be the first major shakeup to the
memory/storage hierarchy since the SSD - with potentially bigger ramifications
because it's byte-addressable.

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shahar2k
so, as someone naively excited about memristors I've noticed the similarity
between Xpoint and memristive memory... am I totally off here though?

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wmf
XPoint is a form of chalcogenide resistive memory while HP memristors are
titanium dioxide resistive memory.

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shahar2k
is this a measure to avoid patent conflicts? (or is there an appreciable
difference in inner workings)

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brennanpeterson
Not a patent issue. PCM is also a NOR flash device, and have been used for
decades in shipping memories.

The answer to your paranthetical depends a bit on how much detail you care
for. Both devices are types of resistive crosspoint memories. In XP, the
resistor is a chalcogenide that has a low resistance polycrystal line state,
and a high resistance amorphous state. These are tuned by the program pulse
length. In TiO2, the mechanism is (presumably, perhaps debatebly) filamentary
bridges between electrode, which can be eliminated by reversing the voltage.

So on one level, both are resistive memories. On another, we are comparing a
bulk phase transition driven by pulse control to a filamentary transition
driven by voltage.

Finally, the more important difference is the selector. PCM devices can use a
chalcogenide based threshold switch. That is the OTS on the XP diagrams. That
selector is the key to functional, dense memory arrays, and the existance of a
matched selector is what makes PCM functional. I haven't seen what the matched
selector for memristors is.

Worth reading recent material from Crossbar on these topics.

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pitaj
One thing I wondering is what Micron is planning on doing with 3D Xpoint. It
was a joint venture between the two firms, after all, but it seems like Intel
is the only one doing anything with it so far. I haven't even heard anything.

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wtallis
Micron has shown a few prototypes, like an SSD using a controller from CNEX
Labs, who are best known for their open-channel SSD work.

I didn't really expect that Intel would end up this far ahead of Micron in
bringing 3D XPoint to market, but it has been clear for quite a while that
Intel has the dominant role in their relationship.

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ChuckMcM
That will change things. I really would like a nice hibernate function that
didn't require saving anything to disk.

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Moral_
Why? Hibernating to an SSD is pretty fast already.

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nine_k
Imagine zero-draw "hibernation mode" taking a few milliseconds to enter, and
"waking up" in a few milliseconds, too. Apply to mobile devices.

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vbezhenar
Mobile devices have battery, so they can power RAM allowing sleep. Also I've
read that Optane is power-hungry, so it won't be used in mobile devices
anyway.

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userbinator
This reminds me of core memory, which was intrinsically nonvolatile and likely
has more endurance per bit than any flash-based storage today. I wonder how it
handles wear leveling, since being in a DIMM format means the CPU(s) can write
to it far more aggressively than an SSD.

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ajmurmann
It doesn't require wear leveling like SSDs do. It's like RAM in that regard.

I strongly recommend this talk from StrangeLoop on persisted memory:
[https://youtube.com/watch?v=VE1hCUMLHX4](https://youtube.com/watch?v=VE1hCUMLHX4)

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pilif
_> It doesn't require wear leveling like SSDs do. It's like RAM in that
regard_

Are you sure? The article lists a fixed durability of 30 drive writes over 5
years. If it wasn’t wear leveling, those 30 writes would be reached very
quickly on specific locations.

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wmf
30 drive writes per day, which is over 50K writes total. But at RAM speeds you
could hit 50K writes in no time (XPointHammer? you heard it here first), so
wear leveling would probably be a good idea. And here's my favorite wear
leveling paper: [http://researcher.watson.ibm.com/researcher/files/us-
moinqur...](http://researcher.watson.ibm.com/researcher/files/us-
moinqureshi/papers-sgap.pdf)

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Zekio
sad part is you gotta combine it with an EPYC cpu otherwise people can
potentially grab your DIMMs and read the data

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wmf
Epyc has SEV encrypted memory and Skylake has SGX encrypted memory (although I
wouldn't expect SGX to actually work with XPoint).

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hguhghuff
With free added back door!

