Use this tag for questions related to the Intel MCS-51 (commonly called 8051) and derivative chips.
The Intel MCS-51 (more commonly known by the name 8051) is a single chip microcontroller series developed by Intel in 1980 for use in embedded systems.
Intel's original versions were popular in the 1980s and early 1990s and enhanced binary-compatible derivatives remain popular today. It is an example of a complex instruction set computer, and has separate memory spaces for program instructions and data (Harvard architecture).
For more detail, refer to the Wikipedia page.