Single, Multi, Triple and Quad-Level SSDs

In May last year, Micron started shipping out the world’s first quad-level cell SSD, and were quickly followed by Samsung. So, what does this new flash storage technology offer?

Developed by Toshiba in 1989, the NAND flash architecture had become the industry standard for the flash storage industry by 2000. NAND flash is non-volatile, which means it doesn’t need power in order to maintain its data. Nowadays, most flash storage devices contain NAND flash memory, primarily due to its smaller chip area compared to NOR memory, and its non-volatile nature. NAND flash memory broadly falls into four categories: single-level cell (SLC), multi-level cell (SLC), triple-level cell (TLC), and the newest version, quad-level cell (QLC).

Single-level cell (SLC) memory stores one bit in each cell, and has faster transfer speeds, along with higher cell endurance, with a lifetime of around 50,000 to 100,000 program/erase cycles, and lower power consumption. SLC flash memory is typically used in high-performance memory cards, and as such, costs more. Multi-level cell (MCL) memory stores two bits in each cell, and as such, transfer speeds are lower, cell endurance is lower, and power consumption is higher. However, because there are double the bits in each cell, the manufacturing cost is lower. MLC flash is typically used in standard consumer flash storage devices. Triple-level cell (TLC) memory, as you might imagine, stores three bits in each cell, resulting in slower transfer speeds and lower cell endurance than SLC and MLC flash chips. However, TLC memory requires less power to operate than MLC memory, and is cheaper to manufacture. TLC flash chips are typically used in memory devices where speed and reliability are less important than cost.

Quad-level cell (QLC) flash chips store four bits per cell, and means lower price and higher capacity solid-state drives. The downside, however, is lower endurance and performance, but the advances in manufacturing technology mean that this new form of NAND flash is more than viable for light use. In May last year, Micron unveiled the first quad-level cell SSD, aimed at the business market, the 5210. The SSD is marketed towards businesses with read-centric workloads due to QLC flash being more sensitive to write wear. The SATA SSDs come in storage capacities ranging from 1.92TB to a whopping 7.68TB, and Micron are firmly pitching them as a viable replacement for businesses’ hard disk drives (HDDs). While Micron have been targeting the business market, Samsung have also unveiled QLC SSDs, this time targeted at the consumer market. Samsung’s QLC SSDs come in 1TB, 2TB and 4TB models.

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