Brief overview of 8051 microcontroller

In1981, Intel Corporation introduced an 8-bit microcontroller called the 8051. This microcontroller had 128 bytes of RAM, 4K bytes of on chip ROM, two timers, one serial port, and 4 ports all on a single chip. 8051 is an 8-bit processor, meaning that the CPU can work on only 8 bits of data at a time.
         ...(Reference: The 8051 microcontroller and Embedded systems by-Mazidi)