QLC vs TLC SSD
Published: Updated:
Spec-based comparison. We have not tested these products. NAND labels, TBW, warranty periods and post-cache write speeds below come from the linked Samsung datasheets and brochure.
Short verdict
TLC stores three bits per cell; QLC stores four. More bits per cell raise density (and usually lower price per gigabyte) but cut the endurance budget the manufacturer publishes as TBW. Samsung’s client SATA examples on the same MKX controller make the trade-off concrete: the 870 EVO lists “Samsung V-NAND 3bit MLC” (industry TLC) with a 5-year / TBW limited warranty; the 870 QVO lists “Samsung 4bit MLC V-NAND” (industry QLC) with a 3-year / TBW limited warranty (870 EVO datasheet, 870 QVO datasheet, 870 EVO / QVO brochure).
Both drives advertise up to 560 / 530 MB/s sequential read / write while their Intelligent TurboWrite (SLC-style) buffer is active. After that buffer is exhausted, the datasheet footnotes diverge sharply — that is where QLC vs TLC shows up in the published numbers, not in the headline table.
Key differences (1 TB examples)
| TLC example — Samsung 870 EVO 1 TB | QLC example — Samsung 870 QVO 1 TB | |
|---|---|---|
| NAND row on datasheet | Samsung V-NAND 3bit MLC | Samsung 4bit MLC V-NAND |
| Common industry name | TLC (3 bits/cell) | QLC (4 bits/cell) |
| Sequential read / write (main table) | up to 560 / 530 MB/s | up to 560 / 530 MB/s |
| Sequential write after Intelligent TurboWrite | 530 MB/s (1 TB / 2 TB / 4 TB) | 80 MB/s (1 TB) |
| TBW (1 TB) | 600 TB | 360 TB |
| Limited warranty | 5 years or TBW, whichever first | 3 years or TBW, whichever first |
| Capacities in line | 250 GB – 4 TB | 1 TB – 8 TB |
Sources: 870 EVO datasheet footnotes 3, 6–8; 870 QVO datasheet footnotes 3, 7–8; brochure TBW table.
What the differences mean
Bits per cell, not a different interface. QLC and TLC are NAND cell organisations. They do not change whether the drive is SATA or NVMe; see NVMe vs SATA for the host interface choice and What is an SSD? for the broader stack.
Headline writes can look identical. Both 1 TB examples list 530 MB/s sequential write because measurements are based on Intelligent TurboWrite. The brochure states that TurboWrite buffer size scales with capacity (up to 42 GB for the 1 TB model; up to 78 GB for 2 / 4 / 8 TB models) and that performance may not be sustained once data exceeds that buffer (brochure).
After the buffer, QLC drops further in these datasheets. For the 1 TB QVO, sequential write after TurboWrite is 80 MB/s; for 2 / 4 / 8 TB QVO it is 160 MB/s. The matching 1 TB+ EVO stays at 530 MB/s after TurboWrite (870 QVO, 870 EVO). Those are Samsung’s CrystalDiskMark / IOmeter figures on its own test PCs — not our measurements.
Endurance and warranty track the cell type in this pair. At 1 TB, EVO 600 TBW / 5 years vs QVO 360 TBW / 3 years; warranty covers the stated period or the TBW, whichever comes first. Samsung defines TBW as the total amount of data that can be written before the drive is likely to fail (brochure).
When QLC is the trade buyers make. The QVO line reaches 8 TB on SATA; the EVO stops at 4 TB in the same brochure. High capacity and lower cost-per-GB for mostly-read archives is the usual QLC pitch; sustained large writes and higher TBW budgets favour TLC in this datasheet pair.
FAQ
Is “3bit MLC” the same as TLC? Yes in industry usage. Samsung’s datasheet row says “3bit MLC” for the EVO and “4bit MLC” for the QVO; the bit count is what matters (870 EVO, 870 QVO).
Does QLC always mean slower everyday use? Not from the headline sequential numbers alone — both list 560 / 530 MB/s with TurboWrite active. Long continuous writes that exceed the SLC-style buffer are where these datasheets show QLC slower.
Does this apply to every QLC or TLC SSD? No. Controllers, DRAM, host interface and firmware differ by model. Always read that model’s datasheet; this page uses one matched Samsung SATA pair as a worked example.