Every SSD, from a cheap boot drive to a blazing Gen5 monster, stores your games and files in NAND flash memory. Understanding how NAND works demystifies nearly every SSD spec you will ever read: TLC versus QLC, endurance ratings, why drives slow when full, and why they get faster each generation. This is the foundation under all of it.
How NAND Stores a Bit
NAND flash stores data by trapping electrical charge inside microscopic memory cells. The amount of charge represents the stored value, and the cell holds that value without power, which is why an SSD keeps your data when the PC is off. Cells are grouped into pages for reading and writing, and pages into larger blocks for erasing. This page-write, block-erase structure shapes everything about SSD behavior.
Bits Per Cell: The Density Ladder
| Type | Bits per cell | Relative endurance | Cost per GB |
|---|---|---|---|
| SLC | 1 | Highest | Highest |
| MLC | 2 | High | High |
| TLC | 3 | Moderate | Moderate |
| QLC | 4 | Lower | Lowest |
Storing more bits per cell packs in more capacity for less money but makes each cell slower to write and quicker to wear, because the controller must distinguish more charge levels. This single trade-off explains why TLC is the mainstream gaming choice and QLC is the budget bulk-storage option.
3D NAND: Building Upward
Early flash laid cells side by side on a flat plane, and shrinking them further hurt reliability. The industry solved this by stacking cells vertically in layers, called 3D NAND. Modern drives stack well over a hundred layers, dramatically increasing density and lowering cost without cramming cells dangerously close together. More layers is a big reason capacities keep climbing while prices fall.
Why Writing Is the Hard Part
Because NAND erases in whole blocks but writes in pages, changing existing data requires the read-erase-rewrite dance that causes write amplification. It is also why deleted data is not truly gone until TRIM and garbage collection clean up. Reads, by contrast, are simple and cause no wear, which is why gaming, being mostly reads, barely stresses a drive.
Putting It Together
The controller ties it all together: it manages the mapping table, spreads writes evenly for wear leveling, runs the SLC cache, and handles error correction. A quality controller with DRAM makes cheap TLC feel fast and reliable, while a weak controller makes even good flash stumble. That is why two drives with the same NAND can perform very differently.
FAQ
Is QLC flash bad?
No, just different. QLC offers the most capacity per dollar with lower endurance and slower sustained writes. For a read-heavy game library or media archive it is perfectly good. For a heavily written OS or scratch drive, TLC’s higher endurance and speed are worth the extra cost.
Does NAND flash lose data over time?
Charge in cells can slowly leak, but powered drives refresh data automatically, so in normal use you never notice. Data retention only becomes a concern for drives left unpowered for very long periods. For an everyday gaming PC that is used regularly, your data stays safe.
Bottom Line
NAND flash stores data as trapped charge in cells, packed denser as SLC, MLC, TLC, or QLC and stacked in 3D layers to boost capacity. Its page-write, block-erase nature explains write amplification, endurance ratings, and why drives slow when full. Reads cause no wear, which is why gaming is gentle on SSDs. Understand NAND and every SSD spec finally makes sense.
