One of the major differences between ANSI and Unicode is that the former is a very old character encoding scheme, whereas the latter is the newer of the two. As you would expect, ANSI has so many shortcomings. In contrast, Unicode comes with some important features which make it a better choice. For instance, ANSI is a width fixed character encoding scheme and uses just 8 bits to represent a character.
This means ANSI can only be used to represent up to 256 characters. On the other hand, Unicode uses 32 bits to represent a character i.e., four bytes for a character. However, since Unicode can use either fixed width or variable width, character encodings like UTF-8 and UTF-16 can be used to represent a character. Although ANSI can still work on current computers, it is not as fast as Unicode. In contrast, Unicode only works on current computers.