OSDev.org

What must I read. I wish understend design and work of OS.

Please be a bit more considerate when asking a question.

You can start following the Bare bones that can be finded in the wiki, or also you can follow the Bran's kernel development tutorial.

Well, he should start at the Introduction, and not skip Required Knowledge or Beginner Mistakes... that's why pointing to the start page of the wiki, in my opinion, is much better than pointing right to the copy & paste (& ask the same beginner questions all over again) section ...

If are you begginer, the best article for you is http://os-development.000webhostapp.com/system-assembler.html and http://os-development.000webhostapp.com/system-c.html . It is in Slovak langunge, but you can use translator.

I don't think either of these examples are very good. The page on assembly forgets that SI and DI are registers, and incorrectly claims that you can use [AX] as a memory reference. The page on C doesn't say anything about a cross-compiler.