Types of operating systems
Operating systems can be classified according to:
1.Number of tasks.
2.Number of users.
3.Human computer interface(HCI).
Classification according to tasks
Single program operating system
Single program operating system allows processing of only one user program in the main memory at a time.This means that the user can only run one interactive program at a time.Then the user must exit from the program before loading and running another program.An example of a single user operating system is MS DOS from Microsoft Corporation.
Multitasking operating system
This type of operating system allows a single CPU to execute what appears to be more than one program at the same time.However,internally only one program is being executed at a time.The CPU switches its attention between programs as it receives requests for processing,executing statements from one program,and then from another using the concept of giving a time slice to each application.This switching of attention is so fast that it appears as if the programs are being executed simultaneously.
Classification according to number of users
Single user operating system
A single user operating system is designed for use by only one person.It cannot support more than one person and runs only one user application at a time.
Multi user operating system
Multi user or multi access operating system allows more than one user to interactively use the computer.It can be installed on a computer that is
accessed by many people at the same time.Examples of such operating systems are UNIX,Novell and Windows NT/2000,Linux.
Classification according to interface
The term human computer interface refers to the method of interaction between the computer and the user and determines how easily the user can operate the computer.The underlying principle in operating system design is to make complex tasks very simple for the user to carry out.This is the reason why a lot of time has been spent by software developers in trying to come up with user friendly interfaces.
Currently the three main types of human computer interface are:
Command line Interface
The user interacts with a computer by typing a command at the prompt found on a command line.A computer reads instructions from the command line and executes them.For a command to be more user friendly,the words used should be descriptive verbs e.g.print,copy etc.Unique abbreviations can also be used e.g.Del Ren Chkdsk etc.
For example,if you are using MS DOS operating system,you can copy a file called Fruits.Dat from a hard disk C to floppy disk A as follows:COPY
C:\Fruits.Dat A:\
NB:The user must press the enter key for the command to be executed
Examples of command line interface are the early versions of MS DOS,PC DOS,OS/2,and UNIX. MS DOS Interface
Menu driven interface
This type of interface provides the user with a list of options to choose from.The interface therefore is suitable for beginners who may have difficulties recalling commands.
Some operating systems present the user with simple menus while others have sophisticated menus.The user makes a selection`by typing any of the letters I,V,E,D or Q to activate a sub menu.
Later versions of DOS came with a menu driven interface called the DOS shell or DOS editor
The graphical user interface(GUI)
The GUI is the latest effort to make the user-interface more user friendly.Besides menus,GUI make use of rectangular work areas called windows,graphical objects called icons and most commands executed using a pointing device (cursor).The features are given an acronym WIMP which stands for Windows,Icons,Menus and Pointing devices.
Examples of GUI based operating systems are OS/2s ,Presentation Manager,Microsoft Windows,Linux and Apple Macintosh.