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Difference Between XLS and XLSX


XLS and XLSX are two file extensions that are used by the very popular spreadsheet application from Microsoft named Microsoft Excel. XLS is very popular as it has been the default format for Microsoft Excel since it was first created up till 2003. In the Microsoft Office 2007 release, Microsoft decided to change the default file format to a different format and adding and additional x for all their document extensions; for Excel, this ended up as XLSX.

As XLSX is a full departure from the older file format that is used in older Excel applications, it is not readable in versions of Excel prior to 2007. This incompatibility hampers the fast adoption of the new software and Microsoft quickly addressed this issue by releasing a patch that allows older Office applications to read the new XML based file formats. As always, backwards compatibility is always a priority for Office applications. Despite adopting and promoting the new XLSX format, newer versions of Excel are still able to open and save documents to the older XLS format. Although it is worth noting that Microsoft Excel 2007 has dropped support for older file formats that were commonly found in MS-DOS.

As we look deeper into the differences between XLS and XLSX, we can see that the way the information is stored is vastly different for both XLS and XLSX formats. XLS is based on BIFF (Binary Interchange File Format) and as such, the information is directly stored to a binary format. On the other hand, XLSX is based on the Office Open XML format, a file format that was derived from XML. The information in an XLSX file is stored in a text file that uses XML to define all its parameters.

As XLSX is stored in a text file format, Microsoft decided to remove macro support for this file format. Instead they assigned a totally different file extension that allows the use of macros; it is named XLSM. The older XLS file extension does not have this issue and it is able to hold spreadsheets that contain macros or not.

XLS is the default file format for the 2003 version of Excel and older while XLSX for versions since 2007
XLS is readable by all Microsoft Excel versions while XLSX is only readable by versions 2007 and later
XLS is a proprietary binary format while XLSX is based on Office Open XML format
XLSX is not able to support macros while XLS is

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  1. Further FYI on .xlsx format:

    Microsoft has stated several benefits to using the new .xlsx format including reduced file size, increased security, improved interoperability between Office products, and better file recovery technology. In terms of the file size issue, it is reported that the new .xlsx file can be up to 75% smaller than previous .xls files. Excel automatically compresses the .xlsx file (using ZIP compression) when the file is saved, and uncompresses it when it is re-opened. The compression allows for easier and quicker transfer of files between computers or over a network.

    The .xlsx format is essentially a container but Microsoft has introduced new terminology to reflect its new open formats. Instead of calling their structure a container, they have chosen the word “package”. Inside the package are three groups of “parts”. The first group contains three individual parts that store information about document properties, application properties, and customized document properties. The second group contains the data for the individual worksheets, while the third group stores information about styles, charts, and strings. The third group of parts is stored relationally to each individual worksheet.

  2. Thank you Kevin for the information. I was looking for confirmation as to whether or not I should save my spreadsheets in *.xls over the *.xlsx format. When I work on my notebook using Excel 2007, I have no problem, but when I go to another computer to show the spreadsheet with colleagues using either Libreoffice or Gnumeric, I get formatting problems when opening my *.xlsx files. The *.xlsx file is problematic because it nearly always has formatting errors when open in any other software besides Excel. If you have a suggestion, I’d appreciate it.


  3. Thanks for all the valuable information. However, my primary doubt was that if we store the excel file in a binary format .xlsb, will it really dilute or damage any data in the excel sheet as the file size becomes considerably small for sharing on a network, when compared to .xls or .xlsx.

  4. My file is in xlsx format. I was working on that n it suddenly got closed n not opening since Den. Wat is the prob.

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