DIMM – The Memory Guy Blog

With 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’s Inside an Optane DIMM?”

Micron Technology has introduced a 32GB NVDIMM-N. Perhaps the most important thing about this device is not so much its high density as the fact that it runs at higher bus speeds than competing NVDIMMs, doing 2933 megatransfers per second (MT/s), a speed that Micron representatives tell us is required to support Intel’s Skylake processor.

Up to this point NVDIMM-Ns have been limited to 2400 MT/s, which is fast enough for Broadwell, but which misses the mark for Skylake. Design is tricky even at this slower speed, requiring a number of expensive high-speed multiplexers in the DRAM’s critical speed path.

“Multiplexers?” Yes, NVDIMMs use them, even though no other kind of DIMM does. The Memory Guy can explain why, having just finished a report covering the NVDIMM market and technology.

Here’s a little refresher for those who either don’t remember or never knew that NVDIMM-N requires multiplexers. The NVDIMM-N looks to the system like a standard Continue reading “Micron’s Super-Fast New 32GB NVDIMM”