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Toshiba mulls hybrid flash and spinning drive

SSD + HDD = SSHD

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Toshiba is considering building a hybrid solid state hard drive containing flash memory and a spinning disk.

Tech-On reports that the company announced its NAND flash strategies in Japan on May 11. Toshiba said: "The hybrid of HDD and SSD enables to save energy. It enables to save energy by about 80 per cent compared with a storage device consisting of only HDDs."

We could view this as a 2-tiered device with fast access flash fronting a slower speed but much higher capacity hard drive. Accesses to the flash would not require a head movement and that would save energy - but not, one would have thought, 80 per cent. That suggests the hard drive would be spun down or rotating slowly for a lot of time.

Toshiba also said it was considering building solid state drives (SSD) for data centre use, meaning it would compete with STEC and others. It will start mass production of 64-bit chips using a sub-30nm process technology this summer. It currently fabricates 32nm chips and says the same microfabrication techniques can be used for the sub-30nm process, thought to be in the 29-25nm range or possibly 24nm.

Its NAND plans call for offering chips for mobile applications, high-capacity and high-performance applications. Single-level cell (SLC) technology will be used for the high-performance market, with some multi-level cell (NMLC) chips; these will also be used for mobile applications.

Toshiba said it was considering a post-flash memory technology called BiCS (Bit Cost Scalable) with memory cells stacked in many layers. It's understood that this doesn't simply involve stacking NAND cells one above the other, but stacking metal layers with insulating layers between them. Holes are cut through this and filled with doped silicon to make pillars.

The metal layer and pillar joint area forms a flash cell in what Toshiba calls a silicon-oxide-nitride-oxide-silicon (SONOS) structure. It is thought this is block-addressable like flash and not bit-addressable like phase-change memory.

Intel and Numonyx recently announced Stacking technology for their phase-change memory (PCM), a technology proposed by them and Samsung to follow on from NAND flash.

Toshiba stated it would decide whether to go ahead with BiCS later this year. ®

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