I tried to use the breadboard-1-6.zip to burn a Atmega328p on a breadboard as in the tutorial.I did this on a Windows 10 PC. At first burning seemed to work, but not the uploading. In the board manager I saw the entry "Atmega on a breadboard (8 Mhz internal clock)".
- uninstall Arduino and manually erase all files from "Program files"- reinstall Arduino IDE 1.8.5The entry "Atmega on a breadboard (8 Mhz. internal clock)" was still there ! allthough there was no more boards.txt containing that message !
The board manager should display the entries that are listed in boards.txt but in the case of my windows 10 PC the board manager does not take its list from there but from somewhere else on my PC and that cannot be changed ....
Now I am figuring out how I was so lucky to have an additional board on W7 simply by replacing the boards.txt and by putting a bootloader directly into C:\Program Files(x86)\Arduino, because that seems not to work on my W10 PC.
So if you edit C:\Program Files(x86)\Arduino\hardware\arduino\avr\boards.txt it will make no difference.
This is true on my W10 PC. I can assure you it is not true on my W7 netbook. I can edit that file in the Program Files directory at will and it is reflected in the IDE when I restart it.
The editing of the original boards.txt was mentioned somewhere on my quest for a 1 Mhz bootloader, but I don't recall where I found it. I think there exists even a Boards.txt.Editor just to do that.