What is the difference between NAND and NOR Flash?

Though they are both considered leading non-volatile Flash memory technologies, NAND and NOR Flash meet completely different design needs based on their individual attributes. 
NOR offers faster read speed and random access capabilities, making it suitable for code storage in devices such as PDAs and cell phones.  However, with NOR technology, cells must be handled one by one, making write and erase functions slow compared to NAND.  NOR also has a larger memory cell size than NAND, limiting scaling capabilities and therefore achievable bit density compared to NAND.  Since code storage tends to require lower density memory than file storage, NOR’s larger cell size is not considered a concern when used in these applications.
Conversely, NAND offers fast write/erase capability and lags in the area of read speed.  NAND’s fast write/erase speed combined with its higher available densities and a lower cost-per-bit than NOR make it the favored technology for file storage in a host of consumer applications.  Offering users the ability to rewrite data quickly and repeatedly, NAND is typically used for storing large quantities of information in devices such as Flash drives, MP3 players, multi-function cell phones and digital cameras. 

The following diagram compares NOR and NAND read, program and erase speeds: