Xeon

What’s Inside an Optane DIMM?

Part of Optane DIMM LogoWith the release of its Cascade Lake family of processors today (formally called the “2nd Generation Intel Xeon Scalable processor”) Intel disclosed more details about its Optane DIMM, which has been officially named the “Intel Optane DC Persistent Memory.”  This DIMM’s architecture is surprisingly similar to an SSD, even to the point of its having error correction and encryption!

The Memory Guy doesn’t generally cover SSDs, but I do cover DIMMs, so this is one of those posts that I could have put into either of my blogs: The Memory Guy or The SSD Guy.  I have decided to put it here with the hopes that it will be easier for members of the memory community to find.

The internal error correction, the encryption, and the fact that 3D XPoint Memory wears out and must use wear leveling, all cause the Optane DIMM’s critical timing path to be slower than the critical path in a DRAM DIMM, rendering the Optane DIMM unsuitable for code execution.  This, and the fact that XPoint writes are slower than its reads, all help to explain why an Optane DIMM is never used as the only memory in a system: there is always a DRAM alongside the Optane DIMM to provide faster Continue reading

What Memory Will Intel’s Purley Platform Use?

Part of Intel Purley SlideThere has been quite a lot of interest over the past few days about the apparently-inadvertent disclosure by Intel of its server platform roadmap.  Detailed coverage in The Platform showed a couple of slides with key memory information for the upcoming Purley server platform which will support the Xeon “Skylake” processor family.  (A review of this post on 7/13/17 revealed that The Platform’s website has disappeared.  The above link and the next one no longer work.)

One slide, titled: “Purley: Biggest Platform Advancement Since Nehalem” includes this post’s graphic, which tells of a memory with: “Up to 4x the capacity & lower cost than DRAM, and 500x faster than NAND.”

The Memory Guy puzzled a bit about what this might be.  The only memory chip technology today with a cost structure lower than that of DRAM is NAND flash, and there is unlikely to be any technology within the leaked roadmap’s 2015-2017 time span that will change that.  MRAM, ReRAM, PCM, FRAM, and other technologies can’t beat DRAM’s cost, and will probably take close to a decade to get to that point.

Since that’s the case, then what is this mystery memory?  If we think of Continue reading