Unix: The Unix Philosophy

Essentially, UNIX is made up of files. In fact, every aspect of UNIX is looked at as a file. When we write some data to be displayed on screen for example, the data is actually written to a screen file and then a certain device driver in the kernel is activated. This controls a particular device, in our case the screen. And the contents of the screen file are displayed on the screen. Files that relate to hardware are known as "special files".

We have one universal file - unix itself. But this file is broken up into many other smaller file systems. By default, i.e. when we install UNIX, there is one root and two user file systems created. Normally file systems correspond to physical sections of the disk, basically the root file system and many user file systems.

These file systems are again broken up into directories (which are again viewed as files) and files. These directories can further have sub-directories and files giving rise to a hierarchical tree-like structure.

In DOS, we sometimes divide the disk into logical sections like C and D. Each of these logical drives has its own set of directories and files. To move from one drive to another we just need to specify the drive as the DOS prompt and hit enter.

But while we are at one drive we can access a file from another drive. Now both these drives are always available by default. In UNIX there is a slight difference. While the root file system and the two user file systems that are created by default are loaded, access to any other file system is only possible if they are explicitely mounted. Mounting means nothing but loading them into memory. And considering that file systems are viewed by UNIX as files, if a time comes for them to be accessed, they have to be in memory (as like any other file).

For example, the floppy drive. This too is considered by UNIX as a file. And read or write to a floppy drive is first done in a "special file", from which then the contents are transferred to actual floppy. But to be able to access the floppy drive through the file connected to it, the file has to be mounted i.e. in memory.