The AT89C51 is an 8-bit CMOS microcontroller that combines a versatile CPU and flash memory on a single chip. It's a low-power, high-performance device that's compatible with the industry-standard MCS-51 instruction set and pinout. The AT89C51 has the following features:
4K bytes of Flash programmable and erasable read-only memory (PEROM)
128 bytes of RAM
32 I/O lines
Two 16-bit timer/counters
A five vector two-level interrupt architecture
A full duplex serial port
On-chip oscillator and clock circuitry
Three-level program memory lock