Two SSDs. Same capacity, same M.2 slot, same NVMe label on the box. One costs R900, the other costs R1,600. The shop assistant says they are "basically the same."
They are not. The difference is usually the NAND type, and it is worth understanding before you spend money, because it changes how the drive behaves and how long it lasts.
What the Letters Actually Mean
SSDs store data in memory cells. The letters tell you how many bits each cell holds:
- SLC stores 1 bit per cell. Fastest, longest lasting, very expensive. You will not see this in a consumer drive.
- MLC stores 2 bits per cell. Fast and durable. Largely gone from the consumer market.
- TLC stores 3 bits per cell. The current mainstream standard.
- QLC stores 4 bits per cell. The cheapest per gigabyte.
More bits per cell means more data in the same physical space, which means cheaper drives. That is the whole appeal of QLC. But you pay for it in two ways.
Difference One: Write Endurance
Every time you write to a memory cell it wears slightly. The more bits a cell has to hold, the more precisely its voltage levels have to be read, and the less wear it tolerates before it becomes unreliable.
In practical terms, a TLC drive typically has meaningfully higher rated endurance than a QLC drive of the same capacity. Manufacturers publish this as TBW, or terabytes written.
For most home users this matters less than the internet suggests. If you are browsing, working on documents, and gaming, you are not writing enough data to wear out either type in a normal ownership period. But if you are editing video, running virtual machines, or doing anything that writes large amounts of data daily, TLC endurance is worth paying for.
Difference Two: The Sustained Write Cliff
This is the one nobody explains, and it is the one you actually feel.
Both TLC and QLC drives use a chunk of their memory in a fast SLC mode as a write buffer. When you copy files, they land in that fast cache first. Everything feels quick.
When the cache fills up, the drive has to start writing at its native speed. On a TLC drive, that drop is noticeable but manageable. On a QLC drive, the drop can be severe, sometimes falling below the speed of an old mechanical hard drive.
You will never see this copying a few documents. You will absolutely see it copying 200GB of video files, or restoring a large backup, or moving a Steam library. The transfer starts fast, then falls off a cliff and crawls.
The Honest Verdict
Buy TLC for your main drive. The one Windows lives on, the one you work off daily. The consistency is worth the extra money and it will last longer under real use.
QLC is genuinely fine for bulk storage. A second drive for media, archives, game installs, or files you write once and read many times. QLC reads perfectly fast. It is only sustained writing where it struggles. If the drive's job is mostly holding things, QLC does that job cheaply and well.
Do not buy QLC for a video editing or workstation machine. You will feel it, and you will be annoyed.
How to Tell What You Are Buying
Manufacturers do not always make it obvious. Here is how to find out:
Check the TBW rating. If a 1TB drive is rated well below what comparable drives claim, it is likely QLC.
Look up the specific model, not the range. Manufacturers sometimes change NAND type mid-production within the same product name. Check reviews of the exact model and capacity.
Be suspicious of unusually cheap high-capacity drives. A 2TB NVMe at a price that seems too good is almost always QLC.
Ask. Any decent supplier should be able to tell you. If they cannot or will not, that tells you something too.
What This Does Not Change
Both TLC and QLC NVMe drives are massively faster than a mechanical hard drive, and both are faster than SATA SSDs. If you are upgrading from a spinning disk, even a QLC NVMe will feel like a new machine. Do not let the perfect be the enemy of the good.
The point of understanding this is not to avoid QLC. It is to put the right drive in the right job and not overpay or underbuy.
Not sure which drive suits your use? Tell us what the machine is for and we will give you a straight answer, not the most expensive option.
