How it works

QLC stores four bits in each NAND flash cell, which packs more capacity into the same silicon than TLC (three bits) or older MLC (two bits). More voltage states per cell raise density and cut cost per gigabyte, but they also shrink the margin for error correction and wear. Controllers paper over that with SLC-style write caches, heavy ECC, and wear leveling so everyday reads and short bursts still feel fast.

The cell type is not the interface. A QLC drive can be a Gen3 or Gen4 M.2 NVMe stick, and a few SATA designs still use QLC too. Peak sequential numbers on the box usually describe a fresh drive with an empty SLC cache. After that cache fills on a long continuous write, throughput often falls harder on QLC than on a similar TLC SKU.

When it matters

It matters when you are shopping by dollars per terabyte and how often you rewrite the same space. QLC is a strong fit for cold archives, media libraries, game installs you rarely overwrite, and secondary capacity drives where street price wins. TLC is usually the safer default for the OS/boot drive, photo or video scratch space you rewrite often, and any workload that regularly pushes past the SLC cache for minutes at a time.

Shopping traps: listings that only quote peak read speed, TBW ratings that are much lower than a TLC sibling at the same capacity, and DRAM-less designs that lean on host memory buffer. Match form factor first (M.2 NVMe vs SATA), then compare cell type and TBW before chasing another few hundred MB/s on paper.

A mainstream QLC Gen4 capacity pick, plus a TLC NVMe contrast when rewrite endurance matters more than dollars per TB.

The Crucial P3 Plus 1TB is a PCIe Gen4 x4 M.2 2280 NVMe SSD on Micron QLC (up to about 5,000 MB/s read, about 220 TBW on 1TB): the classic capacity-first QLC example.

The Samsung 990 EVO Plus 1TB is a TLC contrast pick (Samsung 236-layer TLC V-NAND, up to about 7,150 MB/s read, 600 TBW): better when the drive is your daily rewrite path, not just cold storage.

The Samsung 870 EVO 1TB is a 2.5-inch SATA TLC drive for older bays that cannot take NVMe; useful when you are upgrading a SATA-only chassis and still want TLC endurance instead of chasing QLC capacity.

For the three-bit sibling most consumer SSDs still use, read TLC. For the host protocol most M.2 sticks use, see NVMe. For carrying a spare NVMe stick outside the case, see The Best M.2 NVMe USB-C Enclosures in 2026.