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IT Support & Hardware · Intermediate

NAND Flash Cell Types

Classes of flash memory (SLC, MLC, TLC, QLC) defined by how many bits each cell stores.

Definition

SLC stores 1 bit per cell with the highest endurance and speed; MLC stores 2, TLC 3, and QLC 4 bits per cell, increasing density and lowering cost while reducing endurance and sustained write speed. Most consumer SSDs use TLC or QLC with an SLC cache. Enterprise drives rate endurance in drive writes per day (DWPD).

Example

A QLC SSD slows sharply during a long file copy once its SLC cache is full.

Exam tip

More bits per cell = cheaper and denser but less endurance.

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