What is the difference between HTM and HTML? What is the difference between HTM and HTML?

In the process of learning web design, I did not delve into many of the problems I encountered, such as the relationship between html and htm. Today I have specially sorted it out, and I hope it will be helpful to you.
The most common extension for files containing HTML content is .html, but older operating systems like DOS limited extensions to a maximum of 3 characters, so the .htm extension was also used. Although less used today, the .htm extension is still widely supported.
Both are extensions of static web page files. The extensions can be interchanged without causing errors (this refers to opening, but for a link, if it points to an htm file, and that htm file is changed to an html file, then the link cannot be found)
HTML loads faster than HTML . HTML was born in the DOS era of three-character file extensions. HTML was born in the Windows era of supporting multi-character extensions.