Are you looking at an Excel 2003 workbook in Excel 2007? If you are you'll
see compatibility mode after the book name in the title bar and the book
name will have an extension of .xls. If you're working with an Excel 2003
workbook in Excel 2007, you'll have 256 columns and 16,384 rows. If you want
to convert your Excel 2003 workbook to an Excel 2007 workbook which has
16,384 columns and 1,048,576 rows, simply save it as an Excel 2007 workbook
(Office button, Save as, Excel workbook). Close the workbook and reopen it.
It will now be in Excel 2007 format and the book name in the title bar will
have an extension of .xlsx. Excel 2007 allows you to work with both Excel
2007 workbooks and prior release workbooks as well.