When purchasing AVRs note…

• The -10xx means 10MHz max speed, -16xx means 16MHz, etc.
• However, the speed the chip can run at is proportional to the voltage, check the datasheet for the max speed at a given VCC (its near the end)
• The -nnPx means DIP, -nnAx means TQFP and -nnMx means QFN
• The -nnxU means RoHS, -nnxI is not RoHS
• The V postfix means "Low voltage" generally 1.8V+
• The P postfix is 'picopower' which is a different chip fabrication technology, thus Atmega168P is compatible with but slightly different than the Atmega168. P parts can run as low as 1.8V