vim - Vim set columns not working

Question

On Ubuntu 12.04

:version
VIM - Vi IMproved 7.3 (2010 Aug 15, compiled May  4 2012 04:22:36)
Included patches: 1-429

:set columns=84 has no effect as after it :set columns? gives 151. Why setting columns is not respected by vim?

Answer 1

if exists('+colorcolumn')
  set colorcolumn=80
else
  au BufWinEnter * let w:m2=matchadd('ErrorMsg', '\%>80v.\+', -1)
endif