An operating system is an interface between the user and the machine which controls and coordinates the use of the hardware among the various application programs for the various users.
The four types of operating system structures are −
This is the simplest of all the other structures. In this structure, both the system processes as well as the user processes are allowed to access the system hardware.
DOS is a 16-bit operating system.
Here the input is typed with basic system commands.
It allows 2 GB maximum.
It is a free OS.
DOS is usually called as single operating system.
It does not support a graphical interface.
It can perform the fundamental operation
It uses straightforward commands
Lack of flexibility.
Here the OS is divided into multiple layers and is thereby called the layered approach. These layers are cooperative, and each layer will just communicate with its immediate inside and outside layers, and not beyond that.
It is decomposable
It allows good maintenance.
It is difficult to assign functionalities to the correct and appropriate layer
Because of too many layers, the performance of the system is degraded.
Placing of layers should be difficult as no layer can call services of higher layers.
It is a kind of customization of the operating system. When memory is really crucial, instead of having all the services that the operating system provides in the OS, every service is divided into microkernels, and only the required services are picked as per the machine/device design requirements.
Deadlocks and error conditions are possible between components of the system.
In most modern OS development, the kernel is being minimized and a set of modules are being built on top of the kernel and are linked dynamically. The modularized approach is pretty similar to the layered approach but the freedom here is that each module is independent and is allowed to contact any other module as per requirement.
Easy to maintained
Easy to debug and update
It may lose stability