Is Vim compatible with Vi?

Yes. Vim is very much compatible with Vi. You can use the “-C” command-line flag to start Vim in Vi compatible mode:

    $ vim -C

You can also use:

    $ vim -u NONE

You can also set the ‘compatible’ option to enable Vi compatibility:

    :set compatible

If you want to make sure, to start Vim in a ‘nocompatible’ mode to original Vi, supply the -N command line argument:

    $ vim -N