Purpose of an operating system.

An operating system is the essential layer that exists between the BIOS and application software (e.g. word processing, spreadsheet, graphics, database, web browsers etc.). When a user opens a spreadsheet file the correct instruction needs to travel through the operating system and BIOS levels before the appropriate electronic signals are generated which tell the hard drive's reading heads to find and transfer the required data into RAM.

Here are a few examples of operating systems.

Windows.

When windows was introduced by Microsoft in 1985 it repeated the pattern of many earlier Microsoft: It was slow, ugly and underpowered. Eventually, however they got it right, in 1990, Microsoft released Windows 3.0 a version that did a lot of usual things. By then the machines had become fast enough to support Windows. You could write large applications and multi-task. A few useful applications followed. Then a flood of them, as well as even more powerful, cheaper computers to run them on. With Windows 3.1 in 1992 the speed, reliability and functions of the product improved again. Windows for work groups was added some networking capabilities for those who needed them.

Apple.

Apple is a computer company that specializes in personal computers and computer accessories. Apple has produced many different types of products and is primarily known for the advancement of multimedia personal computers. Most people that are involved with video, music, pictures and sound mainly use Apple computers for their projects because of the quality of the equipment that Apple uses. 

Many people view Apple as a runner up in the computer industry because of Microsoft's almost complete control on personal computers. The truth behind Apple and Microsoft is told in some documentaries. They go into great detail about how Apple was ahead of Microsoft and ended up not releasing their products before Microsoft because their ideas get stolen. What the documentaries try to explain is that Apple is not a runner-up company, but rather, a cutting edge company that pushes computers a step futher every day.

Linux.

Linux was initially created as a hobby project by young students, the students that created Linux software had a goal to create an operating system that exceeded some functionality. The Linux kernel is developed and released under the GNU general public license and as such its source code is freely available to everyone. These days other hand guide Linux's ongoing development and there is hundreds of different Linux distributors which are freely available for download. Each is geared for a particular purpose, some even fit onto a single floppy disk.

Command line & GUI.

Operating system user interfaces come in 2 different varieties.

1. Command Line Interface (CLI).
2. Graphic User Interface (GUI).

CLI.

The CLI is the oldest form of user interface. Being present in early operating systems such as UNIX and MS-DOS (Microsoft disk operating system).

It typically features:

• Text-only output.
• Basic command names.
• Limited user help for commands.
• Very basic error messages.

The most well known CLI is represented by  MS-DOS even today it still exists as a command prompt in modern versions of Microsoft Windows operating systems. In the Linux distributions, the GUI is optional, in theory all system functions can be controlled by the CLI. As such it is more powerful and has better user support in the form of online manuals (MAN files) which tell the user in detail how the command may be used.

GUI.

A GUI is based on WIMP (Windows, Icons, Menus & Pointing device) systems as developed in the early 70's by a famous innovator at Xerox PARC. A GUI creates a user-friendly media-rich environment for users to explore, work and play in using a combination of moveable and resizeable windows. representative icons and intuitive point-and-click mouse control. Also the most familiar GUI is represented by Microsoft Windows.

User interface, resource management & input/output.

User interface.

As detailed above in the command line & GUI section, an operating system has to have some form of user interface.

The interface is responsible for:

• Accepting user commands.
• Parsing user commands (working out what the command actually is).
• Displaying error or warning messages when a device fails.
• Informing users of critical system events e.g. system is about to shut down.
• Confirming that a command has been successfully completed.

As we will see, there are 2 basic types of user interface - the command line (CLI) & the graphic user interface (GUI). The trend towards graphic user interfaces has made a computer system much more user-friendly and more approachable for novice users.

Resource management.

Resources found on a modern computer system are:

• Physical memory (RAM).
• Virtual memory (disk space used as RAM).
• Disc cache (RAM storing the most recently accessed data from the disk).
• CPU (the processor, balance between the operating systems 'time' and application 'time').
• Bandwidth (networking. video, bus etc.).

Input & Output.

Modern operating systems are PnP compatible so they tend to recognise new devices when they are first connected. Through the use of a driver, the operating system can communicate with the hardware.

In addition, it is the operating systems job to control the amount of CPU attention that an input/output device receives. An operating system is also vital in scheduling input and output operations so that the CPU is not idly awaiting data.