XLS and XLSX are two file extensions that are utilized by the popular spreadsheet from Microsoft, which is known as Microsoft Excel. An XLSX is different from the older file format that is used in a previous Excel application.
The incompatibility impedes the fast adoption of the new software, and Microsoft quickly addressed this problem by creating a patch that allows older office applications to read the new format. An XLS is stored in a text file format.
Microsoft decided to remove macro support for this file layout. Different file extensions were assigned, which motivated the decision to remove macro support. The older XLS does not have this issue and can hold macro support spreadsheets.