The AVR is a modified Harvard architecture 8-bit RISC single-chip microcontroller, which was developed by Atmel in 1996. The AVR was one of the first microcontroller families to use on-chip flash memory for program storage, as opposed to one-time programmable ROM,EPROM, or EEPROM used by other microcontrollers at the time.
Most commonly used MCU from atmel is atmega328. This tutorial teaches you to program Atmega328. Here we use a 40-pin atmega16pu controller.