UNIX is a multitasking, multiuser, portable, tool extendable, network supportable and scalable operating system. Initially the OS was designed for small to medium computers, however it worked so well that soon enough it was also adopted for the larger ones.
Multitasking is all about doing many things at the same time and not suffering performance penalties. While you are printing a document, you may still want to edit a file, read a book, log into your mail account and so on. You cannot afford to wait for a task to complete and then follow it by another.
True multi-tasking is off course possible with only multiple cores; however, apparent multi-tasking can be achieved by a correct slicing of the processor time, as I will explain in a later article. Multi-user means the same thing as applied to users rather than applications. Again, if three people were logged onto the same computer at the same time, they could not all print a file at the same time. Instead, they can give the commands at the same time and let the OS prioritize it.
Portability is all about writing a code once and just recompiling it to multiple platforms. The C language is portable itself, and UNIX was written so that this trait could be kept. Backward compatibility is also present, so you can upgrade your system with no negative effects on your business.
Linux tools are something special. There is a history beyond them. This is closely related to the invention of the pipes by Doug McIlroy. Doug was working with macros during the 50s and always trying to show everybody how these could be linked together to eliminate the need to make a series of discrete commands to obtain a result.
From here, there was only another step to the creation of pipes perceived as the connection of a stream like a garden hose. This made it possible for an application to link its output to the input of another, and in this way communicating with each other. Therefore, every little application should only achieve a single task, and we can link multiple applications together to complete a task.
We write this small "applications," put them inside a central toolbox, and call them once we need to use one. With this approach, there are two kinds of tools. There are integral utilities that are required for the operating system to work, like the command interpreter. And then there are tools that are not required for the OS, but still offer additional capabilities for the user -- email applications, for instance. The second category can be extended any time with you own tools.
This is UNIX's modular trait. The tools are simple, and in them you can see the cognitive engineering defined by Joe Cadon as a "black box" -- you form an idea of how things work inside it, and in practice it works just as you imagine. The Linux tools are very honest. You will find every tool described in a manual that has a standard. Here you can even find their bugs. This is an inheritance from McIlroy. Look at the teaser below for an example:
