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As I wrote in http://superuser.com/a/293160/38062:

The problem here is the word "filesystem". In the POSIX/Unix/Linux worlds, it is used to mean several different things.

  1. The "filesystem" is sometimes the entire system of files, rooted at / and as presented to applications softwares by the operating system kernel. With this meaning, people talk of POSIX operating systems having a "single filesystem tree", for example.
  2. A "filesystem" is sometimes one (or more) slice(s) of a (or several) DASD(s) — one or more collections of contiguous disc sectors formatted as a single volume with a given format — as demarcated by some disc partitioning scheme. With this meaning, people talk of, say, "formatting my /usr filesystem". "/usr" here is the (expected) mountpoint of the volume, or (in some partitioning schemes) its identifying label.
  3. A "filesystem" is sometimes an abstract joinable tree of files and directories, presented by a filesystem driver (i.e. the VFS layer) to the rest of the system. With this meaning, people talk of, say, "mounting the proc filesystem on /proc" or "using a tmpfs filesystem for /tmp".

You're seeing meaning #1 when you see "/usr/bin filesystem". It's a filesystem tree rooted at the directory /usr/bin. Yes, Linux very much does have the concept of directories.

Meaning #2 and meaning #3 are what you're mis-reading it as. People are not talking about /usr/bin as an on-disc data set, demarcated by disc slicing/partitioning. Nor are they talking about /usr/bin as a particular type of filesystem driver, or a particular disc volume format.

Further reading

  • Ramesh Bangia (2010). "file system". Dictionary of Information Technology. Laxmi Publications, Ltd. ISBN 9789380298153. p. 224.
  • File System. "Base Definitions". The Open Group Base Specifications. Issue 7 IEEE 1003.1. The Open Group. 2013.
  • Binh Nguyen (2004-08-16). "filesystem". The Linux Dictionary. Version 0.16. p. 616.