Bootloader Hex file

anyone got any idea about which hex file to use from which directory to bootload a atmega328p?

i am actually searching for the same file!

Look in a directory like:

<installation path>\arduino-0022\hardware\arduino\bootloaders\optiboot

You might use the optiboot_atmega328.hex file perhaps.

On a Mac it would be a bit different but you could search for a similar place.

The IDE normally can find that automatically, but you might need to know where it is if you are using a different programmer.

On a Mac, the default location would be:


However, to actually see the corresponding directories, you need to select the file 'Arduino' or 'Arduino,app' in your 'Applications' folder and do 'Show Package Contents' in the context menu (right mouse button or control left mouse button), as the IDE comes as application package.