Atmega328 With UNO Boot-loader (Optiboot)

This is an Atmega328P-PU chip in DIP package loaded with Arduino UNO Bootloader, which is known as Optiboot . Fuse bits are also configured for UNO, ready to run with 16MHz Crystal. Every Atmega328P-PU chip is tested with Arduino UNO board and blinky example is loaded in to the chip whih confirms every chip will work in your project. 

Atmega328P is a low power version and can work with wide varity of voltages and supports 20MHz speed grades. Atmega328 is can only work with 4.5-5.5V range. Atmega328P chip can be used for 3.3V oparations so it removes the need for level converters.