History:
1) In 1981, Intel Corporation introduced an 8-bit microcontroller called the 8051.
2) This microcontroller had 128 bytes of RAM, 4K bytes of on-chip ROM, two timers, one serial port, and four ports (each 8-bits wide) all on a single chip.
3) The 8051 is an 8-bit processor, meaning that the CPU can work on only 8 bits of data at a time.
4) Data larger than 8 bits has to be broken into 8-bit pieces to be processed by the CPU.
5) The 8051 has a total of four I/O ports, each 8 bits wide.
6) Although the 8051 can have a maximum of 64K bytes of on-chip ROM, many manufacturers have put only 4K bytes on the chip.
7) The 8051 became widely popular after Intel allowed other manufacturers to make and market any flavors of the 8051 they please with the condition that they remain code-compatible with the 8051.
8) This has led to many versions of the 8051 with different speeds and amounts of on-chip ROM marketed by more than half a dozen manufacturers.
Inside 8051 Microcontroller:
Companies Producing 8051:
Various Versions of 8051 from Atmel:
