VentureMaker, thanks you for answer on my question.
Now I have the other question. Let's see the example:
Mr. Brown installed WordPress MU 2.6.5 and updated it to version 2.7.
Mr. Green waited for WordPress MU 2.7 out and did fresh install of WordPress MU 2.7.
Is there the difference between Mr. Brown's and Mr. Green's WordPresses MU 2.7? Are Mr. Brown's WordPress MU 2.7 will works 100% without any errors like Mr. Green's fresh installed (without updates) WordPress MU 2.7?
I was studing in the school with deep learning of English language and I am happy, that I am on 90% understand all English text (when reading it, in writing I am not so good). And I am happy, that you helps me. I am so happpy! I am full of happiness. All my words are written without any dictionary.