Friday 16 May 2014

IBM’s Replacement for NAND

New Project Theseus of IBM has some promising and capable ways of replacing the NAND in the long term with a widely higher performance together with better write endurance which would make this technology an excellent choice in storage if someone agrees in the manufacture of the same. IBM had portrayed a new way of memory technology which the company considers to be a replacement for NAND flash someday, and the company’s Theseus Project which is conducted in coordination with the University of Patras in Greece seems to be the first attempt in combining phase change memory, conventional NAND and DRAM on a single controller. The outcome is a hybridized storage solution which outperforms PCIe based SSDs between 12 and 275 times.

Physics of Phase Change Memory

The physics of phase change : The phase change memory is one of those alternative memory structure which has been proposed as a kind of replacement for NAND and the phase change memory operates by rapidly heating chalcogenide glass, moving it between it crystalline and amorphous state. While in its amorphous state which is read as binary 0, the structure has a very high resistance and in its crystalline state which is known as binary 1, the resistance is comparatively low. Phase change memory has the capabilities of quickly shifting between the two state and research done from Intel and Micron have also demonstrated the feasibility of intermediate states that enables two bits of information which can be stored in each cell.

Hybrid Structure for Effective Leverage

Moreover phase change memory has a much lower latency than NAND with a much faster read, write times in theory, and can tolerate millions of write cycles when compared to30,000 high end SLC NAND as well as few as 1,000 with TLC NAND. Besides, it is also well positioned compared to various other theoretical memory devices and NAND flash has huge economies of scale with billions invested in fab plants all across the globe. IBM along with Theseus has incorporated a small amount of PCM into a hybrid structure for effective leverage with its ultra-low latency characteristics.

3D NAND Better Choice

These early PCMs were built on a 90 nm CMOS at very low density where modern NAND flash is available presently in 512Gbit size when compared to 128Mbit for PCM. It is a compact order of magnitude which is faster than a commercial NAND accompanied with superior write performance with data longevity. Though there lies a problem where IBM makes a point that its PSS solution utilises 90nm memory which is produced by Micron, who earlier this year gave notice that it would be cancelling all of its PCM production and would be pulling out of the industry, while leaving the door open to revisit the memory tech sometime in the near future, they also indicated that the superior scaling of a 3D NAND would be a better choice inspite of the various problem faced with the technology in short term.

PCM – Promising Next Generation Memory Technology

According to 2013 ITRS report, it was noted that NAND performance was not expected to increase much from its present situation but in fact would be a bit difficult in maintaining current NAND performance while making improvement in density and holding write endurance constant. Presently PCM seems to be a promising next generation memory technology and someone needs to step in the manufacture of it or else it would be a difficult sell.

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