Understanding TLC NAND

@ 2012/02/24
In almost every SSD review we have published, Anand has mentioned how an SSD is the biggest performance upgrade you can make today. Why would anyone use regular hard drives then? There is one big reason: price. SSD prices are still up in the clouds when compared to hard drive prices (especially before the Thailand floods) so for many, SSDs have not been a realistic option. While SSD prices have been dropping for years, if the current rate continues it will still take several more years before a $399 Walmart PC has a reasonable size SSD in it.

Most of the time, SSD production costs are cut by shrinking the die. Shrinking the die is the same as with CPUs: you move to a smaller manufacturing process, e.g. from 34nm to 25nm. In flash memory, this means you can increase the density per die and usually the physical die size is also smaller, meaning more dies from a single wafer. A die shrink is an effective way to lower costs but moving from one process to another takes time and the first batches of the new flash aren't necessarily cheaper. Once the new process has matured and supply has met demand, prices start to fall.

Since die shrinks are a relatively slow way to lower SSD prices and only contribute to steady reduction of prices, anyone looking to push higher capacity SSDs into the mainstream will need something more. Right now, that "something more" is called Triple Level Cell flash, commonly abbreviated as TLC. Read on for our full analysis on TLC, including performance and endurance expectations, as well as detailed explanations of why MLC and TLC degrade quicker than SLC!

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