The SanDisk ULLtraDIMM DDR3 SSD
Late last year SanDisk released a product called the ULLtraDIMM DDR3 SSD which boldly placed NAND flash storage onto a DDR3 module in 200GB and 400GB capacities without any DRAM. The ULLtraDIMM SSD was unique in that it represented one of the first occasions where a retail product featured non-volatile storage on a DDR3-interface. JEDEC, the organisation which mandates standards and interoperability for memory products, clearly believes such devices have a bright future as it announced the NVDIMM standard yesterday, although the official technical document isn't due until later this year.
While NVDIMM might have you thinking about Nvidia it actually stands for Non-Volatile Dual In-line Memory Module. As the name suggests it is a standard which allows non-volatile memory to make use of the DDR memory bus which has much greater bandwidth potential than conventional storage interfaces. The benefit of non-volatile is that memory vendors can effectively create DDR4 SSDs and there will not be data loss on system shut-down like with current software-based RAM Disks. The announced NVDIMM standard is for DDR4 only, at the present moment, but SanDisk's ULLtraDIMM product demonstrates that equivalent technology is possible on DDR3 should JEDEC decide to extend the standard.
The NVDIMM standard contains two products, NVDIMM-N and NVDIMM-F. The first of those, NVDIMM-N, combines DRAM and flash chips on one module. The flash memory provides a replication backup for the DRAM to ensure no data loss in the event of power loss - such functionality would be welcomed in enterprise and business environments. The second standard, NVDIMM-F, is storage only featuring flash memory but no DRAM chips. In this instance of NVDIMM-F system users will need to pair the storage DIMM alongside a traditional RAM DIMM to ensure the system can function.
These NVDIMMs are to be supported in new DDR4 Serial Presence Detect (SPD) codes that will be released later in 2015. To ensure efficient adoption by manufacturers JEDEC has "defined specific signals on the DIMM connector to facilitate plug-and-play implementation of NVDIMMs on standard platforms". JEDEC hopes the new standard will accelerate adoption of these hybrid DIMMs and it claims that NVDIMMs are "in production now by multiple suppliers, with many new product introductions in the coming months".