Storage specialist Western Digital has announced a variant of its 64-layer 3D NAND flash technology, BiCS3, with four bits per cell, boosting single-chip storage capacities from 512GB to 768GB without a major performance loss.

Based on the 64-layer BiCS3 technology developed by Western Digital subsidiary SanDisk in its joint venture with Toshiba, the BiCS3 X4 modules swap out the existing triple-level cell (TLC) storage system for quad-level cell (QLC). Where a traditional single-level cell (SLC) flash module can store two distinct states, equivalent to a binary 0 and a binary 1, in a single digit and TLC stores eight states across three binary digits, QLC - as the name suggests - stores a total of 16 possible states across its four binary digits. The result is the ability to cram 50 percent more data into the same number of cells, but implementation difficulties and performance barriers have kept QLC from mass adoption - until now, claims Western Digital.

'The implementation of X4 architecture on BiCS3 is a significant development for Western Digital as it demonstrates our continued leadership in NAND flash technology, and it also enables us to offer an expanded choice of storage solutions for our customers,' crowed Siva Sivaram, executive vice president for memory technology at Western Digital, during the announcement. 'The most striking aspect in today's announcement is the use of innovative techniques in the X4 architecture that allows our BiCS3 X4 to deliver performance attributes comparable to those in BiCS3 X3. The narrowing of the performance gap between the X4 and X3 architectures is an important and differentiating capability for us, and it should help drive broader market acceptance of X4 technology over the next several years.'

The use of QLC in BiCS3 X4, already proven by existing two-dimensional X4 implementations from the company, boosts the capacity of individual chips from 512GB with TLC-based BiCS3 to 768GB. Western Digital has promised to showcase internal and removable drives based around BiCS3 X4 in August during the Flash Memory Summit event but is so far silent on a date for consumer availability.

Western Digital has also confirmed it will be adding QLC X4 capabilities the BiCS4, the 96-layer version of BiCS announced with Toshiba back in June.


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