Memory manufacturer, Micron has started shipping it’s new QLC NAND (Quad-level cell) based SSDs. Thanks to affordable prices, SSDs have already gotten significantly cheaper in the past half decade, and with QLC NAND that trend will only accelerate. QLC NAND based SSDs will not only be cheaper, but will also offer higher storage capacities, increasing the memory density by 33%.
Let’s dial back a little, what exactly is QLC NAND? Unlike HDDs which are composed of spinning disks, SSDs or flash storage are somewhat similar to system RAM and have no moving parts. SSDs are made up of NAND gates, and the type of NAND technology or NAND cells used determine the memory density, durability and all the other drive specifications.
The first type of NAND was SLC (Single-level cell) NAND. SLC cells can store only 1 bit per individual cell and SLC based drives are really pricey and have limited capacity. On the positive side however, they offer the best speeds and make up the most durable NAND based memory. Each SLC lasts offers 90,000 to 100,000 read/write cycles. Due to the limited storage capacities and steep prices however, SLC isn’t used in consumer SSDs.
SLC was succeeded by MLC (Multi-level cell) NAND. As you might have already guessed, MLC stores two bits per cell and offers increased storage and made NAND storage in consumer PCs a reality. On the down side however, MLC has lower read/write cycles compared to SLC and is relatively slower too. MLC was followed by TLC (Triple-level cell) NAND, and it was TLC that allowed adoption of SSDs in consumer PCs on such a large scale.
TLC allows three bits to be stored per cell, and although it’s far less durable than SLC, the speeds are still considerably higher than traditional optical HDD drives. It has made SSDs cheaper than ever and is commonly used in tablets and smartphones. With the basic explanation for NAND based storage out of the way, lets discuss Micron’s QLC NAND now.
Micron’s QLC NAND is a 64 layer 3D NAND that allows four bits to be stored per cell, makings up 16 voltage states. As already stated, QLC will be slower and less durable than even TLC but it should become more popular thanks to the low cost. As per Micron, their QLC NAND can endure 1,000 read/wire cycles. Note the difference between SLC and QLC. Apart from PCs, QLC NAND will be used in Data Centers only to store infrequently-accessed data, so endurance and performance aren’t a priority.
Despite that, QLC NAND SSDs are still significantly faster than HDDs, take up comparatively meager space and draw lesser power. Furthermore, HDDs drop into lower power states when they are idle, and returning to normal increases the response time notably. In contrast, SSDs return to their active states almost instantly. As per Micron, it’s QLC SSDs draw 10% less power during a heavy workload than an HDD and 3X less power during read-centric workloads.
QLC NAND based SSDs should have approx 1 DWPD (Drive Write Per Day) of endurance. Micron reached this level of endurance with standard error correction techniques, so even higher levels of endurance might be possible with advanced data correction techniques in the future. Micron also claims that the QLC SSDs adhere to JEDEC’s endurance requirements. JDEC’s requirements basically state that enterprise SSDs have to retain stored data for three months without power after endurance has been exhausted.
For now, Micron has only manufactured QLC NAND drives that use a SATA interface. With time, NVMe and PCIe based QLC NAND based SSDs should also start appearing in the market. And lastly, since this is a joint venture by Micron and Intel, expect Intel to be the only manufacturer to to sell QLC NAND based in the consumer PC space. Micron will most likely focus on the Data Center market, while Intel should experiment with both. Exact specifications will be revealed later on.