As you might have noticed here in the news, Toshiba announced its QLC based NAND (vertically stacked) last week. Basically this NAND type scrams more data in less cells and from that point of view, it is a notch below TLC NAND memory. Toshiba now claims that QLC (quadruple-level cell) can be written a thousand times, that’s similar towards TLC.
QLC-NAND is based upon 64-layer stacked NAND cells that can produce a capacity of 768 gigabit, allowing for 1.5 TB of storage per package (!). That means this type of NAND will bring high volume SSDs in vicinity, availability while remaining very cost-effective.
Basically this type of NAND thus writes 4 bits per cell. Adding more bits per cell also has an effect on the life-span of the NAND cell, and thus that brings down the number of times it can be written. Much like TLC (Triple level cell) many new technologies like error-correction mechanisms and wearing have increased the life-span of the respective SSDs. For example a 500 GB TLC based SSD can quite easily manage a 300TB written before NAND cells start to die off. TLC has roughly a 1000 PE cycles, and that is not the claim for QLC as well, a 100 PE cycles.
How Toshiba managed to achieve a 1000 P/E cycles remains a bit of a mystery thus far. Perhaps they increased the size of the physical memory cell. Manufacturers are already testing with QLC NAND as the first samples have been shipped out. When QLC based SSDs will be available in stores remains unclear.
