[rbanffy]

> If I use Linux I can load a number of different filesystems. Are these not part of the OS?

Actually, most filesystems are part of the kernel. There is the FUSE mechanism, on which you can attach user-space file systems. Filesystem drivers attached in such way are usually (unless you are doing something wrong) portable across OSs that share similar mechanisms and, as the name implies, are withing the user space. not OS-space.

> it is often a feature of the OS

Much like tires are a feature of a car. The fact you bought them together does not mean they are the same object. A tire is not a car much like a GUI is not an OS.

[icebraining]

Never said they were the same thing. My original post was "is part of the OS".

OS space

Again, that's kernel space. OS is something bigger. Debian is an OS. GNU/Linux is an OS. Linux by itself isn't.