4.1 The Operating System
4.1.1 Components of an operating system
Operating Systems (OS) are software programs that control thousands of operations, provide an interface between the user and the computer, and run applications. An OS is designed to control the operations of programs such as web browsers, word processors, and e-mail programs. Today, most computer systems are sold with an operating system already installed. Computers that are designed for individual users (called personal computers or PCs) have operating systems that are designed for individuals running less complex jobs than a server would run. 

With the development of processor technology, computers have become capable of executing more and more instructions per second. These advances have made it possible to run operating systems that are capable of running many complex tasks simultaneously. When a computer needs to accommodate concurrent users and multiple jobs, Information Technology (IT) professionals usually turn to faster computers that have more robust operating systems.

Computers that are capable of handling concurrent users and multiple jobs are often called network servers or simply "servers". Servers have operating systems installed called Network Operating Systems (NOS). A fast computer with a NOS installed may run a large company or a large Internet site, which involves keeping track of many users and many programs.

There are three basic elements that make up the major design components of any operating system. These components are described as modular because each has a distinct function and can be developed separately: 

  • User interface – A user interacts with the computer OS through the user interface. Simply put, the user interface is the part of the operating system that a person can use to issue commands by either typing them at a command prompt or pointing and clicking the mouse on the screen of a Graphical User Interface (GUI).
  • Kernel – This is the core of the OS. The kernel is responsible for loading and running programs (processes) and for managing input and output.
  • File management system – The file management system is what the OS uses to organize and manage files. A file is a collection of data given a single logical name called a "filename". Virtually all of the information that a computer stores is in the form of a file. There are many types of files, including program files, data files, text files, and so on. The way an OS organizes information into files is called the file system. Most operating systems use a hierarchical file system in which files are organized into directories under a tree structure. The beginning of the directory system is referred to as the root directory.