The 8051 is a Harvard Architecture, CISC instruction set, single chip microcontroller. It is a very popular 8 Bit microcontroller. It has a typical RAM memory of 128 or 256 bytes and ROM or Flash memory of 4KB to 64 KB. It can have external memory of 64 KB. Typical peripherals include two UARTS, Two Timers, and Four general purpose PORTS, interrupt pins etc. With a 12 MHz clock frequency the 8051 can execute 1 million one-cycle instructions per second or 500,000 two-cycle instructions per second.
The 89v51 variant comes with features such as 64KB on chip flash and In-System Programming, 12 clock or 6 clock operation, Three timers, 3 counters etc. It can be operated up to 40 MHz.
In many engineering schools the 8051 microcontroller is used in introductory microcontroller courses.
The Micro-51S is a development board with minimum features on-board. Most of the pins as brought out on headers for interfacing standard peripherals by the user. Basic programming interface and headers are available on the board.