Samsung is giving 3D V-NAND a little TLC

Samsung's 3D flash memory, known as V-NAND, powers its 850 Pro SSD and looks to be a compelling alternative to traditional flash memory.

V-NAND achieves higher bit densities by stacking multiple cell layers on top of one another. This approach avoids the interference and patterning issues that chipmakers have encountered when shrinking traditional flash memory based on planar technology. In theory, V-NAND should scale to much higher densities than conventional flash.

Multi-level stacking isn't the only weapon in Samsung's arsenal, though. The firm's more conventional triple-level cell (TLC) flash achieves higher densities on a single plane by cramming three bits into each cell, one more than the usual multi-level cell (MLC) config.

Now, we've learned that the TLC technique is being applied to 3D V-NAND.

During the Q&A session of its SSD Global Summit in Seoul, South Korea, Samsung told us that it plans to make an announcement related to three-bit V-NAND. We don't know when that announcement will come or what it will entail—Samsung's SSD department is notoriously stingy with details—but it's worth noting that Samsung's second-gen V-NAND announcement mentioned "higher-density" drives due later this year. Those would be good candidates for TLC V-NAND.

Before the haters start piling on, it's worth noting that V-NAND's benefits should balance TLC's baggage to some extent. TLC gets a lot of flak because storing an extra bit reduces the write speed and endurance of individual flash cells. However, V-NAND's reduced interference enables a simpler programming algorithm that improves write performance. Also, its 3D charge trap cells have higher endurance than planar equivalents based on floating gates. In other words, V-NAND and triple-level cell storage would seem to be nicely complementary technologies.

For consumer SSDs, TLC's drawbacks seem largely inconsequential, even with traditional NAND. The TLC-based Samsung 840 Series in our SSD Endurance Experiment wrote hundreds of terabytes before burning out, which is far more than typical folks need. And its successor, the 840 EVO, already uses a clever SLC cache to offset TLC's slower write speeds. Given everything, then, Samsung should have all the tools it needs to make a compelling consumer drive based on TLC V-NAND.

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