What Is Flash Memory (NAND / NOR)?
Flash memory is a high-density, fast, electrically erasable and writable persistent memory. It's the block-based, far higher-capacity form of EEPROM.
How Does It Work?
Like EEPROM it holds charge on an insulated gate but does the erase in block/page units. Erasing in blocks instead of individual bytes gives very high density and low cost.
NAND vs NOR Difference
NOR Flash does fast random reads and suits running code directly (XIP); it's small and expensive. NAND Flash is very dense and cheap, ideal for large data storage but accessed page-based.
| Property | NOR | NAND |
|---|---|---|
| Read | Fast, random | Page-based |
| Density | Low | Very high |
| Use | Code (firmware) | Data storage |
Write Endurance and Wear Leveling
Flash also has a limited erase cycle. SSDs and memory cards extend the life with wear leveling, which spreads writes across all cells.
Where Is It Used?
SSDs, USB drives, memory cards, phone storage and microcontroller program memory.
Common Mistakes
- Expecting byte erase: Flash erases block by block, not byte by byte like EEPROM.
- Excessive writing: without wear leveling certain cells wear out early.
- Using NAND for code: NOR is usually more suitable for direct execution.
Frequently Asked Questions
Which Flash does an SSD use?+
What's the difference between Flash and EEPROM?+
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