Placing the above inside your .vimrc file will draw a vertical line inside vi. This is helpful if your coding style prefers to not have lines over a certain length.
I'm pretty sure this doesn't work in vi. Vim >= 7.3 only.
By the way, here's the generic version of config (doesn't not error if option is not present):
Extending on @dmedvinsky
au BufWinEnter * let w:m2=matchadd('ErrorMsg', '\%80v.\+', -1)
will emulate colorcolumn by simply coloring the overflowing characters.