What is ANSI format?

Question

What is ANSI encoding format? Is it a system default format? In what way does it differ from ASCII?

Answer 1

Basically "ANSI" refers to the legacy codepage on Windows. See also an article by Raymond Chen on this topic:

The source of this comes from the fact that the Windows code page 1252 was originally based on an ANSI draft, which became ISO Standard 8859-1.

The first 127 characters are identical to ASCII in most code pages, the upper characters vary, though.

However, ANSI does not automatically mean CP1252 or Latin 1.

All confusion notwithstanding you should simply avoid such issues nowadays and use Unicode.