XLS Vs. XLSXby Collier Jackson
Starting with Microsoft Excel 2007, the default file extension for spreadsheets is .xlsx instead of the older .xls. The "x" at the end stands for "XML," which means Extensible Markup Language -- a method of encoding documents. Although you will typically not need to view the XML used to produce the spreadsheet, if you do it will appear as a series of headers, tags and data. This text then becomes the spreadsheet you see when you open Excel.
If you've ever downloaded a "zipped" file from the Internet, you know that it is considerably smaller than the contents inside the file. The .xlsx file type allows Excel to automatically compress files by "zipping" them when you close the program and "unzipping" the files when you open the program. This means that you will save hard drive space with the new file format as the program automatically compresses all the files.
If you open an .xls file and a warning appears notifying you that the file is corrupt, there is often nothing you can do to view the file contents. As XML stores information as separate containers within the file -- even if one section is corrupted, you can still open the file and view the information that has not been damaged.
XML saves certain information separately from your document, such as the comments, notes and hidden rows and columns. If you want to share the document with another person or organization, the .xlsx file extension allows you to make these sections invisible to the other party. This can be helpful if you need to hide sensitive information but don't want to create an entirely new spreadsheet.
Macros are pieces of Visual Basic script that can be run from inside a spreadsheet. While often helpful, they can be used maliciously. The .xls file extension doesn't let you know if any macros are present in the spreadsheet, but the .xlsx file format does, because it cannot be used with documents that contain macros. Spreadsheets with macros will save as .xlsm files by default.