XLS and XLSX extensions represent popular Excel file formats that were introduced by Microsoft as part of its Office suite over a period of time. XLS being the oldest and widely used file type is also known to be the Excel97-2003 file format. The XLSX file format was introduced as a replacement of XLS file type with the launch of Excel 2007. Common users may not know the underlying differences between the two file formats, however, XLS is different than XLSX file format in several ways as detailed below.


So what is it that is actually different between XLS and XLSX? Following is a list of differences between the XLS and XLSX file formats.

The File Format Difference

The underlying file format is what makes the main difference between the XLS and XLSX files.

XLS files are based on the Binary Interchange File Format (BIFF) and store information in binary format as per XLS File Format Specifications.  Data is arranged in an XLS file as binary streams in the form of a compound file as described in [MS-XLS].

In contrast, an XLSX file is based on Office Open XML format that stores data in compressed XML files in ZIP format. The underlying structure and files can be examined by simply unzipping the .xlsx file. A sample XLSX file when renamed to .zip and extracted, its contents can be observed in a folder as any other folder of files.

Support for Macros

XLS files, being old format, provided the support for Macros which are programs that are written by end-users and are used for automation of tasks such as opening files, data comparison, etc. Macros at one end facilitate users to automate tasks, but on the other hand can be risky as well since these run directly when you open an Excel file.

In contrast, XLSX files do not support Macros. If you need to embed and execute Macros, you will have to save your file as XLSM which is an Excel Open XML Macro-Enabled spreadsheet file format.

Excel Supportability

XLS files can be opened with all versions of Excel due to the backward compatibility. However, XLSX can only be opened with Excel 2007 and lateral versions only.

Have any further queries about the internal details of XLS or XLSX file formats? You can get in touch with file format experts over the file format forum to have guidance for your questions.