Atmel's AVR microcontrollers have an 8 bit RISC core running single cycle instructions and a well-defined I/O structure that limits the need for external components.

The wide range of available devices from 8pin/1K Flash to 100pin/256K Flash and the high degree of integration make it an ideal choice for low cost, small dimensions to medium range applications from small actuars/sensors up to embedded WEB server applications.

The AVR devices are available in two families TINY and MEGA.

All devices have the same core while the MEGA devices have more instructions than the TINY devices.

The AVR RISC is a Harvard architecture with separate buses and address space for program and data memories, load and store operations and a 32 bytes register file.
The AVR has up to 133 instructions [PDF 663KB] which are either 16/32 bit wide and 80% of these are executed in a single cycle