The Mac innovated many things in filing systems, and took things in new and better directions. What is it.
File extension have many problems.
Realistically you probably have more like 20,000. Apple created a four letter file type . On the Mac type is denoted by what a file's icon looks like. For example, if it looks like a little painting or drawing, then chances are it is a painting or drawing file. If it looked like a puzzle piece, then it was a system extension.