VI and Vim

• Functionally, vim is almost a proper superset of vi. Therefore, everything that is in vi is available in vim.

• Vim tries to resemble the syntax and semantic of Vi command as much as possible. But being an "improved version", Vim adds new commands and features. It also changes the semantic of some Vi commands to better match the current expectations of its programmers.

• Vim can edit files inside a compressed archive (gzip, zip, tar, etc). 

• Vim's Enhancements :

completion, comparison and merging of files (known as vimdiff), a comprehensive integrated help system, extended regular expressions, scripting languages (both native and through alternative scripting interpreters such as Perl, Python, Ruby, Tcl, etc.) including support for plugins, a graphical user interface (known as gvim), limited integrated development environment-like features, mouse interaction (both with and without the GUI), folding, editing of compressed or archived files in gzip, bzip2, zip, and tar format and files over network protocols such as SSH, FTP, and HTTP, session state preservation, spell checking, split (horizontal and vertical) and tabbed windows, Unicode and other multi-language support, syntax highlighting, trans-session command, search and cursor positionhistories, multiple level and branching undo/redo history which can persist across editing
sessions, and visual mode.