Hardware

NAND Flash

NAND flash is the non-volatile semiconductor memory technology used in SSDs, USB drives, and memory cards. It stores data as electrical charge in floating-gate transistors and retains data without power. NVMe was designed specifically to exploit NAND flash's parallel, high-speed I/O characteristics.

NVMe Storage

NAND Flash and NVMe Storage

NAND flash is organized into cells, pages, and blocks. Reading a page takes ~50–100µs; erasing a block (required before rewriting) takes ~1–3ms. NVMe's parallel queue model is designed to hide this erase latency by issuing thousands of concurrent operations across many dies simultaneously.

NAND Cell Types

  • SLC (Single-Level Cell) — 1 bit per cell. Fastest, most durable (~100K write cycles), most expensive. Used in write-intensive enterprise SSDs.
  • MLC (Multi-Level Cell) — 2 bits per cell. Good balance of performance and cost. Enterprise and high-end consumer use.
  • TLC (Triple-Level Cell) — 3 bits per cell. Mainstream SSDs. Lower cost, lower endurance (~3,000 write cycles).
  • QLC (Quad-Level Cell) — 4 bits per cell. Highest density, lowest cost, lowest endurance. Used for read-heavy or archival workloads.

3D NAND

Modern NAND stacks cells vertically in 100–200+ layers ("3D NAND"). This increases density without shrinking the cell size, improving both capacity and endurance compared to planar NAND. All major enterprise NVMe SSDs use 3D NAND.