About Maximum number of columns

Hi All.

I have a question about the Maximum number of columns in a table ?

In FAQ for PostgreSQL,I can find this description :
  Maximum number of columns in a table?
          250-1600 depending on column types
But , I want to know what type is 1600 limit , and what type is 250
limit . it is important for me  , thanks .

Regards ,
zhao xin