ANSWER: The most obvious difference is size. The parallel port on the back of your computer is a 25-pin port, while the serial port has room for nine pins. But the real difference is in the way the… ...

But there are two big problems: 1) nobody knows the percentage of existing serial workloads that can be usefully parallelized (but it's probably small), and 2) parallel programming is hard.

Of course, the basic difference between NAND and NOR serial flash memory is the underlying transistor architecture. Both are available as parallel memory as well, with the same characteristics.