NAND flash stores data in a little cloud of electrons in a quantum well. The presence or absence of charge - or the strength of the charge - tells us what bits are stored.
ReRAM stores data through changes in the resistance of a cell. There are a variety of ReRAM technologies in development, including phase-change memory (PCM) and HP's memristors, based on at least a half-dozen competing materials.
Expect healthy competition as the industry and buyers sort out the details.
While different implementations have different specs, all ReRAM has key advantages over today's common NAND flash.
- Speed. ReRAM can be written much faster - in nanoseconds rather than milliseconds - making it better for high-performance applications.
- Endurance. MLC flash - the most common - can only handle about 10,000 writes. ReRAM can handle millions.
- Power. Researchers have demonstrated micro-Amp write power and expect to get in the nano-Amp range soon, which makes ReRAM much more power efficient than NAND flash, which requires voltage pumps to achieve the 20 volts required for writes.
The Storage Bits take
NAND flash will retain advantages in cost and density for the foreseeable future, meaning that it will be here for decades to come. So where will ReRAM fit in the storage hierarchy?
- Data integrity. Losing a snapshot is no big deal. Losing your checking account deposit is. Mission critical applications will prefer ReRAM devices - and can afford them.
- Performance. Today's SSDs go through many contortions to give good performance - and don't succeed all that well. A fast medium removes complexity as well as increasing performance.
- Mobility. Depending on how the never-ending tug-of-war between network bandwidth and memory capacity develops, consumers may come to prefer large capacity storage on their mobile devices. If so, ReRAM's power-sipping ways will be an asset on high-end products.
Toshiba is well-positioned to enter these high-end markets with SSDs analogous to today's 15k disks. It may not be a huge market, but the margins will make it worthwhile.
Other vendors, including Panasonic, Micron and Samsung, are also working on ReRAM products. Another interesting question: to what extent will fast ReRAM replace DRAM in systems?