What is cMLC Flash?
Some recent news mentioned cMLC flash, which is short for “consumer MLC.” This term is used to differentiate between the cheapest available product, mainstream MLC, and products that are aimed at the computing segment, and thus carry higher price tags.
There are several of these higher-end products. Some have longer endurance, like eMLC and SLC flash. Some have faster interfaces, like ONFi and Toggle Mode. Then there are the combinations of these: a fast interface with enhanced reliability.
There are disadvantages to these. The consumer market still drives NAND flash economics, accounting for more than 90% of flash revenues. This means that any other product is considered a niche product and commands a higher price. Today SLC is sold for nearly ten times the price per gigabyte of MLC NAND (see the SSD Guy for more on this), and eMLC commands a lower premium, but is still costly. Enterprise MLC – eMLC – has higher endurance than standard MLC flash, but achieves this by slowing the product’s read and write access. The faster interfaces are not commonly used (they are nearly exclusively found in SSDs) so they also carry a hefty price premium.
Clearly any design that uses cMLC NAND flash will carry a decided cost advantage over any of these alternatives. For this reason there is a strong impetus on SSD makers to use cMLC NAND rather than other types of NAND flash.
Over the long run 3-bit flash (that with three bits per cell) is likely to displace today’s MLC as the low-cost volume product, although this product, also called TLC, has significantly lower endurance and higher error rates, so it has found limited acceptance to date. As flash controllers become more sophisticated they should be able to offset some of these issues.