The Operating System determine the type of processing that a computer system is able to perform, since it controls the allocation and use of the computer resources.
Operating systems can be classified according to;
1. Number of tasks that the system can perform concurrently.
• Single-tasking (program) operating system.
• Multi-tasking operating system.
2. Number of users the system can support at the same time.
• Single-user operating systems.
• Multi-user operating systems.
3. Human Computer interface (i.e., how the user and the computer interact).
• Command line.
• Menu driven interface.
• Graphical user interface (GUI).
Classification according to tasks handled concurrently.
1. Number of tasks that the system can perform concurrently.
• Single-tasking (program) operating system.
• Multi-tasking operating system.
2. Number of users the system can support at the same time.
• Single-user operating systems.
• Multi-user operating systems.
3. Human Computer interface (i.e., how the user and the computer interact).
• Command line.
• Menu driven interface.
• Graphical user interface (GUI).
Classification according to tasks handled concurrently.
Single-tasking OS.
Single-tasking OS allows only one user-program in the main memory to be processed at a particular time.
This means that, the user can only run one interactive program at a time. The user must then exit from the program before loading and running another program
Multi-tasking OS.
A Multi-tasking OS allows a single CPU to execute/process more than one program, all of which are m memory, at the same time.
Each program is allocated a time-slice.
In this case, the programs take turns at short intervals of processing time. The CPU switches its attention between programs as it receives requests for processing, executing statements from one program, and then from another.
The programs to be run are loaded into the memory and the CPU begins execution of the first one. When the request is satisfied, the second program is brought into memory and execution starts on the second program, and so on.
In multi-tasking, the computer is able to work on several programs at the same time. It works on the programs on sequence, one after the other, and that at any given instant it executes instructions from one program only. However, the computer works so quickly that it appears to be executing the programs simultaneously.
Classification according to number of users.
Single-user OS.
A single-user OS is designed to be used by only one person. It allow only one user/person to operate the machine at a time in an interactive, conversational mode, and runs only one user program at a time.
Multi-user OS.
A multi-user OS allows more than one user (many people) to interactively use/access the computer at the same time.
Classification according to Human Computer Interface (HCI).
The term Human Computer Interface (HCI) refers to the method of interaction between the computer and the user, and determines how easily the user can operate the computer.
HCI is expected to be "user-friendly", i.e., it should be one that the end-user finds helpful, and easy to learn and use.
Features of a user-friendly HCI.
i). It should be relatively easy for the user to try to start using the system.
ii).The system should be self-contained, so that the user is not forced into accessing manuals.
iii). The amount of effort and the information required for the user to get the system complete required tasks should be minimal.
iv). The system should be robust and reliable, i.e., the user should be protected from unexpected system actions, including system failures.
v). The system should be able to adjust to different levels of expertise between users and also as users grow in competence.
vi). The user should be made to feel in control of what is going on.
vii). The system should behave in a logical and consistent manner, enabling the user to reason about what is going on and apply what has been learned.
Types of User interfaces.
There are different types of Human Computer Interfaces;
1. Command driven interface.
2. Menu driven interface.
3. Graphical User Interface (GUI).
Command driven interface.
This is an interaction between the user and the computer that requires the use of commands The user types a command at the prompt found on a command line.
The computer then reads instructions from the command line and executes them.
Commands enable the user to quickly instruct the computer what to do.
Command-driven software is more flexible, but it is more difficult to learn.
The user must know what commands are available, what they do and how they should be typed. For this reason, commands are most popular with experienced technical persons, such as computer Operators, Programmers or in situations where the end-user continually works with the same program and has therefore mastered the commands.
Disadvantages of using command driven interfaces
This type of interface provides the user with a list of program commands displayed on the screen to choose from and a simple means of selecting between them.
This interface is suitable for beginners and infrequent users who may have difficulties in remembering commands.
There are 2 types of menus;
(a) Pull-down menus — are special types of menu used mostly in Windows.
(b) Pop-up menus and Pop-down menus. These menus are made to appear above or below an item on the screen in order to obtain a choice from a user.
Advantages of Menu driven interfaces
This is an interaction between the user and computer that involves issuing of commands to the computer by activating certain small graphic images displayed on the screen called Icons.
To issue a command, the icons can be selected using a pointing device like a Mouse.
GUI is mostly found on Workstations or PCs fitted with graphic adapters able to support high resolution graphics.
Examples of GUI based OS;
· They are user friendly.
· Easy to learn and use.
Single-tasking OS allows only one user-program in the main memory to be processed at a particular time.
This means that, the user can only run one interactive program at a time. The user must then exit from the program before loading and running another program
Multi-tasking OS.
A Multi-tasking OS allows a single CPU to execute/process more than one program, all of which are m memory, at the same time.
Each program is allocated a time-slice.
In this case, the programs take turns at short intervals of processing time. The CPU switches its attention between programs as it receives requests for processing, executing statements from one program, and then from another.
The programs to be run are loaded into the memory and the CPU begins execution of the first one. When the request is satisfied, the second program is brought into memory and execution starts on the second program, and so on.
In multi-tasking, the computer is able to work on several programs at the same time. It works on the programs on sequence, one after the other, and that at any given instant it executes instructions from one program only. However, the computer works so quickly that it appears to be executing the programs simultaneously.
Classification according to number of users.
Single-user OS.
A single-user OS is designed to be used by only one person. It allow only one user/person to operate the machine at a time in an interactive, conversational mode, and runs only one user program at a time.
Multi-user OS.
A multi-user OS allows more than one user (many people) to interactively use/access the computer at the same time.
Classification according to Human Computer Interface (HCI).
The term Human Computer Interface (HCI) refers to the method of interaction between the computer and the user, and determines how easily the user can operate the computer.
HCI is expected to be "user-friendly", i.e., it should be one that the end-user finds helpful, and easy to learn and use.
Features of a user-friendly HCI.
i). It should be relatively easy for the user to try to start using the system.
ii).The system should be self-contained, so that the user is not forced into accessing manuals.
iii). The amount of effort and the information required for the user to get the system complete required tasks should be minimal.
iv). The system should be robust and reliable, i.e., the user should be protected from unexpected system actions, including system failures.
v). The system should be able to adjust to different levels of expertise between users and also as users grow in competence.
vi). The user should be made to feel in control of what is going on.
vii). The system should behave in a logical and consistent manner, enabling the user to reason about what is going on and apply what has been learned.
Types of User interfaces.
There are different types of Human Computer Interfaces;
1. Command driven interface.
2. Menu driven interface.
3. Graphical User Interface (GUI).
Command driven interface.
This is an interaction between the user and the computer that requires the use of commands The user types a command at the prompt found on a command line.
The computer then reads instructions from the command line and executes them.
Commands enable the user to quickly instruct the computer what to do.
Command-driven software is more flexible, but it is more difficult to learn.
The user must know what commands are available, what they do and how they should be typed. For this reason, commands are most popular with experienced technical persons, such as computer Operators, Programmers or in situations where the end-user continually works with the same program and has therefore mastered the commands.
Disadvantages of using command driven interfaces
- They are more difficult to learn.
- The user must know the command to type.
- It is less user-friendly.
- It is not easy to use, i.e., one is required to master the command format/syntax.
This type of interface provides the user with a list of program commands displayed on the screen to choose from and a simple means of selecting between them.
This interface is suitable for beginners and infrequent users who may have difficulties in remembering commands.
There are 2 types of menus;
(a) Pull-down menus — are special types of menu used mostly in Windows.
(b) Pop-up menus and Pop-down menus. These menus are made to appear above or below an item on the screen in order to obtain a choice from a user.
Advantages of Menu driven interfaces
- Menus provide many options to select from.
- The user is presented with a choice and therefore, does not need to master any commands.
- They are easier to use.
This is an interaction between the user and computer that involves issuing of commands to the computer by activating certain small graphic images displayed on the screen called Icons.
To issue a command, the icons can be selected using a pointing device like a Mouse.
GUI is mostly found on Workstations or PCs fitted with graphic adapters able to support high resolution graphics.
Examples of GUI based OS;
- Ms-Windows,
- Linux,
- Apple Macintosh.
- Programs are represented graphically by use of Icons.
- Commands are selected and issued using pointing devices, e.g., Mouse, trackball.
- There is use of pull-down menus.
- Programs open by displaying windows.
· They are user friendly.
· Easy to learn and use.
