ATMega328 microcontroller bootloader UNO

ATmega328 microcontroller with Arduino Uno Bootloader

The ATmega328 with a pre-loaded Arduino Uno bootloader is great for your more customised designs where you'd like to add Arduino Uno code without buying the Uno board. To enable the bootloader to function exactly like an Uno board you will need a 16 MHz crystal oscillator or resonator, a 5 V power supply and a serial connection.
Features & Benefits of the Uno Bootloader
•32 K program space
•23 I/O lines
•Runs up to 20 MHz
•1.8 V to 5 V operating voltage