Intel's crazy-fast 3D XPoint Optane memory heads for DDR slots (but with a catch)

Surprise! Intel's 3DXPoint memory will go inside a DDR4 slot—but not everyone is happy with Intel's proprietary approach to support.

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Intel / Micron

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It was clear from the beginning that Intel and Micron’s new 3D XPoint memory—which promises “1,000 times” the performance of today’s SSDs—would require a faster pathway into the PC.

After all, SATA, SATA Express, and even PCIe lack the sheer bandwidth to support the levels at which 3D XPoint can perform. But this week Intel officially revealed its plans for 3D XPoint memory support: It will slip into a DDR4 slot, and it’s a decision that won’t make vendors happy.

The story behind the story: When Intel and Micron introduced its jointly built memory, everything seemed rosy. But now that details of how it will be implemented are starting to trickle out, the devil’s hand is becoming apparent.

Intel’s 3D XPoint-based DIMMs are electrically and physically compatible with DDR4, and offer a four-fold increase in capacity. Intel also says the memory offers massive performance benefits without modifications to your OS or applications.

intel dimm

Intel will offer 3D XPoint memory that actually slip into DDR4 slots.

So if all that sounds good, why the grousing? The problem, it seems, is how Intel is rolling out support. While the 3D XPoint DIMM is electronically compatible and pin-compatible with DDR4, Intel’s compatibility solution is proprietary.

Rick Merritt of EETimes first chronicled the unhappy reactions to Intel’s news here. Merritt points out that despite Intel’s claim of being electrically compatible, company officials conceded an entirely new CPU and new extensions will be required to access 3D XPoint.

“They’re extending the (DDR4) interface,” Jim McGregor, an analyst with Tirias Research, told PCWorld in an interview. “It’s going to be electrically and pin compatible, but the way they talk will be different.”

With the only source of the new type of memory coming from a fab jointly owned by Micron and Intel, no one’s going to be happy, McGregor said. ”If you don’t have multi-vendor support, the OEMs are going to backlash,” he said.

McGregor compared the 3D XPoint situation to what happened with Direct RDRAM: Intel tried to push a new memory type and received incredible pushback from memory makers. In that battle, Intel and Rambus created a new type of high-speed, serial memory that no one wanted. The outcry gave Intel a bloody nose, and the company actually had to do a 180-degree turn, dumping RDRAM and embracing the standard that ultimately won: DDR.

McGregor also said memory makers are vexed by a lack of transparency. 

”The main frustration is [Intel and Micron] won’t tell us anything about the damned stuff,” he said.

20150819 151148 Tirias Research

This Micron slide from IDF seems to show 3D XPoint being used quite differently than Intel’s plan.

McGregor said both Micron and Intel were reluctant to answer questions with the other party in the room—an awkward dynamic considering they’re partnering. Nonetheless, it’s worth noting that Micron’s plan for what it does with 3D XPoint differs from Intel’s.

For example, check out the slide above, from Micron’s presentation at IDF. It shows 3D XPoint living on the PCIe bus and actually below the industry JEDEC standard that was announced in May. That standard, called NVDIMM, sounds conceptually closer to what Intel is planning, but the two don’t appear to be compatible from what we know today. JEDEC officials were unavailable to comment.

As a DRAM manufacturer, Micron officials also insist DRAM will be relevant with 3D XPoint, McGregor said. But that doesn’t square with Intel’s statements. The company has said from the beginning that some PC configurations that don’t need the performance of DRAM can use just 3D XPoint. I covered what that world might look like here.

All these concerns, of course, will emerge further down the road. In the near term, we’ll see 3D XPoint-based SSDs that plug into SATA, SATA Express and PCIe slots. It will be a while before 3D XPoint becomes main system memory, and Intel won’t actually ship its 3D XPoint DIMM Xeon until 2017 at the earliest. So even if there are complaints from the industry, it won’t matter any time soon. Furthermore, 3D XPoint benefits might silence critics anyhow. Intel said in one scenario, 3D XPoint systems could come stoked with a 6TB—yes, terabyte—DIMM inside.

That’ll mainly appeal to people running servers and data centers, but Intel has said since the beginning that it will also target 3D XPoint at enthusiasts and gamers (it already pushes rebranded and neutered Xeons into that crowd). So as much as it seems that 3D XPoint is currently a fantasy technology, and we shouldn’t worry about proprietary approaches to compatibility, it will eventually land in a machine for you.

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