Intel 8051 microcontroller family

Intel 8051 and 80C51 are members of Intel MCS-51 family of 8-bit microcontrollers. In addition to on-chip clock oscillator, 2 16-bit timers, 4 I/O ports and a serial port, all 8051 and 80C51 chips have 128 bytes of RAM and 4 KB masked ROM. If necessary, 8051 memory can be expanded up to 128 KB by adding up to 64 KB of external program and data memory.