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📘 How SSDs Work

A solid-state drive stores data in NAND flash rather than on spinning magnetic platters.

6
lessons
~30 min
to learn
Adults
level
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What you’ll learn

  1. A drive made of memoryIdentify NAND flash, the controller, and firmware as the main parts of an SSD.An SSD exposes logical storage while its controller manages a nonvolatile NAND array.
  2. Cells, pages, and blocksExplain how cells, pages, and blocks constrain NAND reads, writes, and erases.NAND stores charge in cells, programs pages, and erases larger blocks.
  3. Programming and readingRelate charge thresholds and bits per cell to SSD density and performance.Programming verifies threshold ranges, while SLC through QLC trade margin for density.
  4. The translation layerExplain logical-to-physical mapping and over-provisioning.The FTL hides relocation and spare capacity gives maintenance operations room to work.
  5. Wear and maintenanceDescribe wear leveling, garbage collection, write amplification, and ECC.Firmware spreads wear, reclaims mixed blocks, corrects errors, and pays an internal write cost.
  6. TRIM and the full pathExplain TRIM hints and trace a logical write through mapping, NAND programming, and background maintenance.TRIM supplies deletion knowledge while the controller pays the physical cost of flash updates and maintenance.

Questions this course answers

What is the key erase constraint in NAND flash?

Pages are the usual programming unit, but erasure operates on larger blocks, so updates require indirection and housekeeping.

Put a simplified flash update in order.

The SSD writes the new version elsewhere, records the mapping, and makes the previous version obsolete.

Match each SSD mechanism to its job.

These mechanisms solve different problems: endurance, reusable space, data integrity, and host knowledge.

What does TRIM primarily communicate?

TRIM or Deallocate identifies ranges that can be treated as invalid during the SSD's own reclamation work.

Why can an SSD write more internally than the host requested?

The logical request is only the visible part of a flash update. Physical organization and maintenance create additional NAND writes.

Grounded in trusted sources

  • Micron Technology, Choosing the right NAND: https://www.micron.com/products/storage/nand-flash/choosing-the-right-nand
  • Micron Technology, Solid-state drives glossary: https://www.micron.com/about/micron-glossary/solid-state-drives
  • Samsung Semiconductor, Solid State Drive white paper: https://semiconductor.samsung.com/resources/white-paper/Samsung_SSD_White_Paper.pdf
  • Samsung Semiconductor, Internal SSD product information (TRIM and garbage collection): https://semiconductor.samsung.com/consumer-storage/support/faqs/internalssd-product-information/
  • Microsoft Learn, TRIM and Unmap hints: https://learn.microsoft.com/en-us/windows/win32/w8cookbook/new-api-allows-apps-to-send--trim-and-unmap--hints-to-storage-media
  • NVM Express, NVM Command Set Specification: https://nvmexpress.org/wp-content/uploads/NVMe-NVM-Command-Set-Specification-1.0a-2021.07.26-Ratified.pdf
  • Wikimedia Commons MediaWiki API image records: https://commons.wikimedia.org/w/api.php

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