Why is "Everything is a file" unique to the Unix operating systems?

So, why is this unique to Unix?

Typical operating systems, prior to Unix, treated files one way and treated each peripheral device according to the characteristics of that device. That is, if the output of a program was written to a file on disk, that was the only place the output could go; you could not send it to the printer or the tape drive. Each program had to be aware of each device used for input and output, and have command options to deal with alternate I/O devices.

Unix treats all devices as files, but with special attributes. To simplify programs, standard input and standard output are the default input and output devices of a program. So program output normally intended for the console screen could go anywhere, to a disk file or a printer or a serial port. This is called I/O redirection.

Does other operating systems such as Windows and Macs not operate on files?

Of course all modern OSes support various filesystems and can "operate on files", but the distinction is how are devices handled? Don't know about Mac, but Windows does offer some I/O redirection.

And, compared to what other operating systems is it unique?

Not really any more. Linux has the same feature. Of course, if an OS adopts I/O redirection, then it tends to use other Unix features and ends up Unix-like in the end.

The idea that "everything is a file" came from Multics. The designers of Unix based a lot of their work on predecessors, especially Multics. Indeed, a lot of things in computing are based on predecessors.

You can read up on the late Dennis Ritchie's work in the design of Unix for more. He referenced things that they "copied" from Multics, such as the tree-like file system, the command shell, and non-structuring of files. I'm not implying that the Unix folks stole from the Multics folks. For all intents and purposes, it was the same folks.

Unique? No. Defining? Absolutely.

Having everything as a file or a device in a known hierarchy means you can use the same set of tools for everything. Plan 9 from Bell Labs takes this further with even hardware devices as files.

More importantly, this allows for two very simple and powerful concepts. Basic utilities that do One Thing Well (tm), which can be strung together with pipes as needed. Want to find something in a text file? Use cat to show it, pass it through grep, and you're cooking with gas. That's the real power of the 'Unix' way - specialised applications working together for massive amounts of flexibility.

Mac OS X also follows the Unix philosophy, but it's better hidden (an 'application' bundle is really a directory full of files), and in fact is a proper, certified Unix, descended from NeXT, which used bits of FreeBSD.

With Windows, there are some binary components such as event viewer and registry since, and there's some speed advantages there, in that particular scenario.