Operating System (OS)

An operating system (OS) is software, consisting of programs and data that runs on computers manages computer hardware resources, and provides common services for executing different application software.

The operating system is the most important type of system software in a computer system.

Without an operating system, a user cannot run an application program on their computer.

For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between application programs and the computer hardware.

Eg:

1. Ms-Windows
2. GU/Linux
3. UNIX
4. MacOS
5. Sun Solaris
6. OS/2
7. Android OS
8. Palm OS

Functions of OS

1. Memory management - is the act of managing computer memory. This involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed.

2. Process management - is an integral part of any modern day operating system (OS). The OS must allocate resources to processes, enable processes to share and exchange information, protect the resources of each process from other processes and enable synchronization among processes.

3. Input / Output management.

4. Acts as an intermediary between application programs and the computer hardware.

5. Manages hardware devices manages and maintains disk file systems and supports application programs.

6. The OS provides you with the tools or commands that enable you to interact with the computer.

7. Loads application programs such as word processing and spreadsheet programs from backing storage into the computer’s main memory.

8. Coordinates how programs work with the computer’s hardware and other software

Types of Operating Systems

There are four major types of Operating systems.

1. Real-Time Operating Systems

These Operating systems support real-time applications. A real-time application is an application that responds to certain inputs very quickly. It accepts inputs, processes the inputs and gives the appropriate response in milliseconds or microseconds.

Real-time applications are used in medical diagnostic equipment, life-support systems, machinery, scientific equipment and industrial machines. Real-time operating systems are very fast.

2. Single-User/Single-Tasking Operating Systems

Allow a single user to perform just one task at a time. A user may at any given time be able to do only one function such as printing a document, editing a text file, saving a file or downloading some content from a network server.

MS-DOS, Palm OS, used on the Palm handheld computers are examples for this type of operating systems.

3. Single-User/Multitasking Operating Systems

Allow a user to perform two or more functions at any given time.

For example an office user may print a very large document in his computer and while it is being printed he may edit another document in his computer, thus increasing his productivity.

Similarly, you may need to share data between two different programs. For example, when you prepare a presentation in MS-PowerPoint you may want to include a graph that you have done in MS-Excel in it.

Windows 95 and Windows 3.1 are examples for this type of operating systems

4. Multi-User/Multitasking Operating Systems

Support more than one user at a time, performing more than one task at a time. Multiple users use programs that are simultaneously running on a single network server called the terminal server.

Examples of Multi-User/Multitasking Operating Systems are UNIX, VMS and mainframe operating systems such as MVS.

Providing a User Interface

When you work on a computer, you see and use a set of items on the screen. Taken together these items area called the user interface. The two most common types of user interfaces are graphical and command line.

1. Graphical User Interfaces

Most current OSs provides a graphical user interface (GUI). They are so called because you use a mouse or some other pointing device to work with graphical objects such as windows, menus, icons, buttons and other tools.

This is sometimes known as a WIMP (Windows, Icons, Mouse, and Pointer) environment too.

The GUI enables you to issue commands to the computer by using these graphical objects rather than memorizing and typing text commands.

2. Command-Line Interfaces

Operating systems such as MS-DOS, UNIX and Linux use a command-line interface, which uses typewritten commands and not graphical objects to execute tasks. Users interact with the OS by typing strings of alphanumeric characters at a prompt on the screen.