What are the differences between NAND and NOR flash?

What are the differences and where would you use each?

Answer

There is a lot of trade-off to it.

Wikipedia also:

Despite the additional transistors, the reduction in ground wires and bit lines allows a denser layout and greater storage capacity per chip. In addition, NAND flash is typically permitted to contain a certain number of faults (NOR flash, as is used for a BIOS ROM, is expected to be fault-free). Manufacturers try to maximize the amount of usable storage by shrinking the size of the transistor below the size where they can be made reliably, to the size where further reductions would increase the number of faults faster than it would increase the total storage available.

So, NOR flash can address easier, but is not even close to as dense.

If you take at a look at a pretty decent comparison PDF.

NOR has lower standyby power, is easy for code execution and has a high read speed.

NAND has much lower active power(writing bits is faster and lower cost), higher write speed(by a lot), much higher capacity, much much lower cost per bit and is very easy for file storage use. due to it's lower read speed when using it for code execution you really need to ghost it to ram.

To quote a small section with a great table above it...

The characteristics of NAND Flash are: high density, medium read speed, high write speed, high erase speed, and an indirect or I/O like access. The characteristics of NOR Flash are lower density, high read speed, slow write speed, slow erase speed, and a random access interface.