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Table of contents
1.
Introduction
2.
What is Layered Structure of Operating System?
3.
Why Layering in Operating Systems?
4.
Design of Layered Operating Systems
5.
Architecture of Layered Structure
5.1.
Hardware 
5.2.
CPU Scheduling 
5.3.
Memory Management 
5.4.
Process Management
5.5.
I/O (Input/Output) Buffer 
5.6.
User Programs 
6.
Advantages of Layered Structure
7.
Disadvantages of Layered Structure
8.
Frequently Asked Questions
8.1.
Describe the objective of a layered operating system.
8.2.
Why is a layered operating system important?
8.3.
Where is a layered operating system used?
8.4.
How can the layered design of an operating system impact system performance?
9.
Conclusion
Last Updated: Mar 27, 2024
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Layered Structure of Operating System

Author Aditya Singh
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Introduction

The operating system has different layers in layer structure to perform other tasks and services. Each layer has its own specific and dedicatedly defined job to accomplish. Layering in an operating system provides a distinct advantage. Each layer can be individually defined and interact as needed, simplifying the creation, maintenance, and updates of the system when organized into distinct layers.

Layered Structure of Operating System

In this article, we are going to discuss the Layered Structure of the operating system in detail. 

What is Layered Structure of Operating System?

The Layered Structure of the Operating System is a way of organizing the different components of an OS into separate layers. Each layer of an operating system is responsible for specific functions and interacts with the layer above and below it. The bottom layer is the hardware layer, followed by the kernel layer, system call interface, and shell layer. This structure helps in modularizing the OS and allows for easier maintenance, development, and debugging.

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Why Layering in Operating Systems?

Layering in operating systems refers to the architectural approach of organizing system components into distinct layers, with each layer responsible for specific functionalities. This design principle aims to enhance modularity, scalability, and maintainability of operating system software. Here's why layering is employed in operating systems:

  • Abstraction: Layering enables abstraction by encapsulating complex functionalities into discrete layers. Each layer presents a simplified interface to the layers above, hiding implementation details and providing a well-defined set of services.
  • Modularity: By decomposing the operating system into layers, it becomes easier to manage and maintain the system. Changes or updates to one layer can be made independently without affecting other layers, promoting modularity and code reusability.
  • Ease of Understanding: Layering promotes a hierarchical structure that makes the operating system architecture easier to understand and reason about. Developers can focus on one layer at a time, facilitating comprehension and troubleshooting.
  • Portability: Layering facilitates portability by abstracting hardware-specific functionalities into lower layers. Higher layers can remain largely unchanged when porting the operating system to different hardware platforms, as long as the interface between layers remains consistent.
  • Scalability: Layering allows for the addition of new functionalities or components by simply adding new layers or extending existing ones. This scalability ensures that the operating system can adapt to evolving hardware requirements and user needs over time.
  • Standardization: Layering promotes standardization by defining well-defined interfaces between layers. This standardization enables interoperability between different components and facilitates the development of third-party software that interacts with the operating system.

Design of Layered Operating Systems

The whole operating system is divided into some layers (say 0 to n). Each layer of an operating system is responsible for its particular function. Some conventions are also there for the implementation of these layers as follows:

  1. The outermost layer must be a UI (User Interface) layer in a layered operating system.
  2. The innermost layer should be the Hardware layer.
  3. Any layer can access the layers present below its own and can't access the layer above it. For example => Layer n-1 has access to all layers from n-2 to 0, but not the nth layer.

Also see, Difference Between Bit and Byte

Architecture of Layered Structure

This operating system was developed as a step forward from the early monolithic systems.

The layered operating system divides the operating system into numerous levels, each with its own set of capabilities.

The following are some guidelines for layer implementation.

  • Layer 0 is responsible for allocating processes and switching between them when interruptions or timers occur. It also covers the basics of CPU multiprogramming.
     

As a result, if the user layer wants to engage with the hardware layer, the response will pass through all layers from n-1 to 1. Each layer must be planned and implemented to only require services from the layers below it.

layered structure of operating system

Hardware 

This layer communicates with the system hardware and manages the operation of all peripheral devices such as a printer, mouse, keyboard, scanner, and so on. The hardware layer is responsible for managing certain types of hardware devices.

The hardware layer is the lowest and most authoritative layer in the layered operating system architecture. It is directly connected to the system's core.

CPU Scheduling 

This layer is responsible for CPU process scheduling. Processes are handled utilizing a combination of scheduling queues. The methods are placed in the job queue as soon as they enter the system. The ready queue contains the processes prepared to run in the main memory.

Memory Management 

Memory management is concerned with memory and the movement of processes from disc to primary memory for execution, as well as the reverse.

Process Management

This layer manages the processes, which includes assigning the processor to a specific process at a given time. It is also known as Process Scheduling. FCFS (first come first served)SJF (shortest job first)Round-robin scheduling, etc methods are used for process scheduling.

I/O (Input/Output) Buffer 

I/O devices are critical in computer systems. They give end-users the ability to engage with the system. This layer looks after the buffers for the I/O devices and ensures that they function properly.

Suppose you're typing on a keyboard. A keyboard buffer is connected to the keyboard and saves data for a limited period. Similarly, all input/output devices are equipped with a pad. This is due to the slow processing or storage speeds of the input/output devices. The computer uses pads to sync the processor and input/output devices.

User Programs 

This is the highest layer in a tiered operating system. This layer is the reason for the many user programs and applications that run on a computer, such as word processors, games, and browsers. Since it is concerned with application programs, it is sometimes known as an application layer.

Must Read Multiprocessing Operating System and File management in operating system

Advantages of Layered Structure

  • Modularity: This architecture promotes modularity because each layer only does its assigned duties.
     
  • Easy debugging: It is relatively simple to debug because the layers are discrete. If a mistake happens in the CPU scheduling layer, the developer can only debug that layer, as opposed to a Monolithic system where all services are present at the same time.
     
  • Easy update: A change made to one layer will have no effect on the other layers.
     
  • No direct access to hardware: The hardware layer is the design's innermost layer. So, unlike the Simple system, where the user has direct access to the hardware, a user can use hardware services but not directly modify or access it.
     
  • Abstraction: Every layer is focused on its own set of tasks. As a result, the other layers' functions and implementations are abstract.

Disadvantages of Layered Structure

  • Complex and careful implementation: Because a layer can use the services of the levels below it, the layers must be carefully arranged. The memory management layer, for example, is used by the backup storage layer. As a result, it must be placed behind the memory management layer. As a result, significant modularity leads to complicated implementation.
     
  • Slower in execution: When a layer wishes to communicate with another layer, it sends a request that must travel through the layers between the two layers to be fulfilled. As a result, unlike the Monolithic system, which is faster, it increases response time. As an output, increasing the number of layers may result in an inefficient design.
     

Read about Batch Operating System and Process Management in OS.

Frequently Asked Questions

Describe the objective of a layered operating system.

A layered structure is a system structure in which the operating system's numerous services are divided into layers, with each layer performing a distinct, well-defined task.

Why is a layered operating system important?

In an operating system, layering has a specific advantage. Each layer can be defined independently and interact with one another as needed. In addition, creating, maintaining, and updating a system in the form of layers is easy. A change in one layer's specification has no bearing on the other layers.

Where is a layered operating system used?

It was designed to improve existing structures such as the Monolithic (UNIX) and Simple structures ( MS-DOS ). For example, this tiered method is used in the Windows NT operating system.

How can the layered design of an operating system impact system performance?

Distributing operating system layers across multiple physical tiers can enhance performance, scalability, and fault tolerance. It simplifies maintenance due to low coupling and facilitates the addition of new functionality, optimizing the OS.

Conclusion

In this article, we discussed Layered Operating Systems. We also discussed the layers of Layered Operating systems and their working. And finally, in the end, we discussed the advantages and disadvantages of Layered operating systems.

Recommended Readings: 

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