There are multiple flash storage options for embedded devices.

NOR Flash

• can be mapped directly int address space
• code can be directly executed from NOR flash
• expensive
• reliable
• arranged into erase blocks (i.e. 128 KiB)
• erasing block: set all bits to 1
• erase cycle damages block slightly: wear leveling
• programming and reading one word at a time
• standard register-level interface: Common Flash Interface (CFI)
• CFI is described in standard JESD68

NAND Flash

• cheaper and available in higher capacities (than NOR flash)
• needs more complex hardware and software
• cannot be mapped to address space
• code and data need to be copied to RAM
• organized into erase blocks (16 KiB - 512 KiB)
• can be only read and written in pages (~2 or 4 KiB)
• erasing block: set all bits to 1
• erase cycle damages block slightly: wear leveling
• extra area per page: out-of-band (OOB) area
• standard register-level interface: Open NAND Flash Interface (ONFi)

Managed Flash

• SD-Card and eMMC
• NAND chips with a controller
• similar interface to hard drive