AVR microcontrollers are Harvard architecture. This means, that in this architecture are separate memory types (program memory and data memory) connected with distinct buses. Such memory architecture allows processor to access program memory and data memory at the same time. This increases performance of MCU comparing to CISC architecture, where CPU uses same bus for accessing program memory and data memory.
As all AVR microcontrollers Atmega microcontrollers are 8 bit RISC microcontrollers. Their core are the same as tiny series, just they are more powerful and has more peripheral devices built in like:
AVR microcontrollers are 8-bit on chip systems. AVR Tiny are very impressive microcontrollers. They small from outside, but inside they are not so small. In side is the same AVR RISC architecture which is compatible to all AVR microcontrollers. They have In system Programming (ISP) Flash memory, internal EEPROM and RAM, timers, interrupt sources, analog comparator, ADC and more.
Development tools for Tiny microcontrollers are the same as for other AVR MCU.
The biggest advantage of tiny microcontrollers is that they are extremely economical.
This applies to all types of AVR microcontrollers because they all use same AVR core technology. So lets go through some of them:
Ability to work at 1MIPS/MHz (MIPS – Millions Instructions Per Second);
On chip Flash memory (now tiny series have up to 8kB, mega up to 256kB) with write cycle not less than 1000 times;
On chip RAM memory (tiny series up to 512B, mega up to 8kB);
On chip EEPROM memory (tiny series up to 512B, mega up to 4kB) with write cycle not less than 100000 times;
Working frequencies up to 20MHz;
Protection fuses from unintentional reading and modification of program and data memories;
Ability to program in system – directly on board using ISP cable;
Four types of clock generators: Internal generator, RC generator of clock cycles, Internal generator with external crystal resonator, and External synchronisation;
Two or three power down modes;
Some microcontroller can work at very low voltages like 1.8V;
AVR microcontroller are 8-bit on chip system with RICS (Reduced Instruction Set Computer) command system. The most of commands are performed in one clock cycle.
In AVR microcontroller reading next command is done during execution of previous command. So the overal number of commands in 1second is almos equal to working frequency.
AVR microcontrollers are manufactured using high quality CMOS technology, contains EEPROM memory inside the chip and differs from other microcontrollers that they require less power in higher frequencies.
Atmel AVR 
