Intel Corporation fabricated the 8 – bit microcontroller which was referred as MCS-51 in 1981. This microcontroller was also referred as “system on a chip” because it has 128 bytes of RAM, 4Kbytes of ROM, 2 Timers, 1 Serial port, and four ports on a single chip. The CPU can work for only 8bits of data at a time because 8051 is an 8-bit processor.8051 microcontrollers use two different kinds of memory such as UV- EPROM, Flash and NV-RAM. Hence 8051 will not be seen in the part number even though it is the most popular member of the 8051 family. Atmel fabricated the flash ROM version of 8051 which is popularly known as AT89C51 (‘C’ in the part number indicates CMOS). The flash memory can erase the contents within seconds which is best for fast growth.