Why does pptx save as a smaller file than ppt?

PPTX files are saved in a compressed XML format, which reduces their file size compared to the older PPT format, which uses a binary file structure. The XML format allows for more efficient storage of data and better compression algorithms. Additionally, PPTX can store images and other media in a more space-efficient manner. This results in PPTX files typically being smaller and easier to share than their PPT counterparts.