I think I remember from one of Kalen Delaney's   
   "SQL Server Internals" manuals - probably the   
   2000 edition - that nulls in columns are stored   
   in one or more extra bytes in a table row's   
   storage, each binary digit representing   
   whether the first / second / third column etc.   
   is NULL in the row.  That means that the NULL   
   state is absolutely separate from possibly storing   
   a column value.  It's "extra" bytes in the sense   
   that it doesn't happen in a table where no   
   columns are nullable.   
      
   I once saw a database that was mangled somehow   
   so that a NOT NULL column returned NULL in one row,   
   presumably because the bit was set that way.   
   That's at least very rare (at least after you   
   install Service Pack 1) unless your hardware   
   lets you down - which ours sometimes has.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)