Why is the bootlaoder necessary?

Why is the bootlaoder necessary?
specific answers please!

To allow the loading of programs without needing a programmer.

Correct spelling, please!

If you use a programmer instead of loading your code over USB then you don't need the boot loader at all.

For safety, a program should not be able to overwrite its own code. A simple error in programming will erase the entire program. This error may be discovered years later (like a leap year) and now you have thousands of dead devices in the hands of thousands of very angry users. "Turn it off and turn it on" no longer works.

Of course that doesn't really matter too much for a hobbyist who wants to reprogram his Arduino twenty times in an afternoon. So the bootloader was invented to circumvent this safety feature on the chip.

The ultimate expression of this is the "Erase" button on the Arduino Due. If you press that button while the Due has power, it will delete your program. There's no "Are you sure?"

Sounds like you haven't looked the 'Learning' tab at the top of this screen.
Suggest you go through the the whole tab.

Also google is your friend.
https://www.arduino.cc/en/Hacking/Bootloader?from=Tutorial.Bootloader

https://www.google.ca/search?q=arduino+bootloader&rlz=1C9BKJA_enCA713CA713&oq=arduino+bootloader&aqs=chrome..69i57j0l3j69i60.5982j0j7&hl=en-US&sourceid=chrome-mobile&ie=UTF-8

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Its not.

PocketHarambe101:
specific answers please!

Homework?