html

The primary difference between .htm and .html is simply that .html can't be represented in a DOS/16 bit operating system which uses the 8.3 file naming convention. So, .html files were renamed .htm when they were written on DOS/Windows 3.x systems. Most servers (but not all) that can handle 4 character file extensions can be set up to treat .htm and .html files exactly the same, just as they can be set up to treat .jpg and .jpeg files the same. I hope you understand.