/nɔːr/
n. “The flash memory that’s built for speed and direct access.”
NOR is a type of non-volatile flash memory distinguished by its ability to provide fast random access to individual memory locations. The name comes from the “NOT OR” logic gate that forms its underlying architecture. NOR flash is commonly used in embedded systems, firmware storage, and applications where code must be executed directly from memory, known as XIP (eXecute In Place).
Key characteristics of NOR include:
- Random Access: Individual bytes can be read and executed directly without copying to RAM.
- Non-Volatile: Retains data even when power is removed.
- Slower Writes, Faster Reads: Writing and erasing is slower compared to NAND, but read access is fast and predictable.
- Durability: High endurance for read-heavy applications, but typically lower density and higher cost than NAND.
- Firmware Storage: Ideal for storing BIOS, bootloaders, and embedded program code.
A conceptual example of NOR usage:
# Bootloader stored in NOR flash (conceptual)
Device powers on → CPU fetches boot code directly from NOR memory
# No need to copy code to RAM before execution (XIP)Conceptually, NOR is like a bookshelf where every book can be instantly grabbed and read without opening a central archive — perfect for frequently accessed instructions.
In essence, NOR flash provides fast, random-access, non-volatile memory ideal for code execution in embedded systems and firmware, complementing NAND’s high-density storage capabilities.