On former days Flash was unknown and internal EPROM very expensive. So most micros are mask programmed in the factory (8051 devices). And so a long time was needed from software development until production. But this cause, that often many programmed devices unneccesary because buggy or antiquated.

So Intel has the great idea to rename such devices as 8031 and sell it also. Because on any 8051 the internal ROM can be switched of with pulling the EA pin low and external EPROM can be connected.

Thus also the 8051 family so popular today. Since connecting external EPROM / RAM was the only way to start with microcontrollers in former days.


Peter