Virtuabotix ATMEGA328P-PU Optiboot Arduino Uno Bootloader
ATMEGA328P-PU Pin-out for Arduino Uno Bootloader & Chip
Clock speed: up to 20 MHz Clock Speed (16 MHz Recomended)
Memory: Flash 32 KB | EEPROM 1 KB |SRAM 2 KB
Pins: Digital I/O Pins 14
Analog input Pins: 6
PWM (Pulse Width Modulation): 6 pins
What is a bootloader?
A bootloader is to a microcontroller what an operating system is to a computer. The Arduino Bootloader provides start up services, and is what allows the chip to be programmed through the serial port, since normally you must program an Atmel chip using a SPI programmer.
The Arduino Uno bootloader is virtually identical to the Arduino Duemilanove bootloader, except for some minor changes to program UART baud rate, and start up order. Because of that anything written for the Arduino Duemilanove can be run on the Arduino Uno.