Saving TBs of storage space without sacrificing transfer time

> Also, I couldn't understand why there were several compression software that only compresses single file. I never knew they could be (and were designed to be) used in combination with tar, until I switched to GNU/Linux.

My first experience with Losedows was in the early 1990s, and at that time you couldn't do much of anything without going into the DOS command line system that Losedows sat on top of. Because of that, you learned quite a bit more about how the OS operated. When Losedows decided to hide their underlying structure and push users to only see the gui stuff most of the time, around about Losedows 95 or Losedows 98, I think it hurt the ability of the majority of users to understand what was happening underneath the gui.

Tar files (aka tarballs) are not compressed. In fact a tarball is a (very) little bit larger than the file(s) it contains. Indeed, a tarball is basically a concatenation of files, each of them preceded by its metadata (its name, its permissions, its owner, its last modification date, ..., and its size, what allows to know where the next file will start).

Compressing tarballs, rather than their individual files, usually provides better compression ratios. Indeed a repeating "pattern" (basically a sub-sequence of bytes) may be shared between the files. For instance if they are plain text files in a same language.