etfsboot.com

Command executable Reference

A .com file is a command executable. In MS-DOS, the COM format was a flat memory image without a header. Modern Windows still ships some tools with this extension, for example more.com and tree.com, but these files have the normal PE format. The command interpreter starts .com files like .exe files. Windows network boot also uses pxeboot.com, a boot program with an F12 prompt.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.