Microcontrollers are classified into two types based on their memory type: those with no on-chip ROM and those with on-chip ROM, The chip without on-chip ROM must be used externally with EPROM (typically 8031); the chip with on-chip ROM is classified as on-chip EPROM (typically 87C51), MASK on-chip mask ROM (typically 8051), on-chip Flash (typically 89C51), and other types.
MCUs are classified into two types based on their intended use: general-purpose and special-purpose. It is classified into4, 8, 16, and 32-bit MCUs based on the width of the data bus and the number of data bytes that can be processed at the same time.
