China DOS Union

How do you compare extension sizes? Is it based on which one has more letters, so it's bigger? Then for TXT and DOC, with the same number of letters, which is bigger and which is smaller????
Also, do subdirectories have extensions?

No way?
Extensions don't have any size distinction. They only distinguish file types, just like a person's ID card, making it easier to identify computer software files. The meanings of various extensions are as follows:
1. BMP, GIF, JPG are image files, and their identities are:
＊.BMP: basic drawing format file.
＊.GIF: images in this format support 256 colors and can be used to make small animations.
＊.JPG: a standard image file that uses the JPEG method to compress image data.
2. WAV, MID, MP3, MPG are media files, and their identities are:
＊.WAV: standard digital audio file.
＊.MID: records each note sent out by a MIDI device as a number, then outputs sound through various monotone mixes and synthesis.
＊.MP3: one of the popular digital sound file formats on the Internet.
＊.MPG: moving image and sound files using the MPG compression standard.
3. There are also some other files that can be identified by their extensions:
＊.HLP: system help file.
＊.BAK: system backup file.
＊.ZIP: archive.

Subdirectories do not have extensions. But extensions can also be used to name subdirectories.

Just use "dir /oe"