In Excel 2003 we had only 65,536 rows and 256 columns. This would gives us 16.7 million cells to work.
In Excel 2010 we now have 1,048,576 rows and 16,384 columns. This more or less 17.1 billion cells on each worksheet witch represents a 102% increase over the old version.
Columns in Excel 2003 where labeled from A to IV. In Excel 2010 they are labeled from A to XFD. This change means that some old range names such as YTD2005 or TAX2006 cannot be used anymore because now they are valid cell addresses. Excel automatically changes this name ranges during conversion. For example, a range name such as YTD2005 will be changed to _YTD2005.