Table of contents

Introduction

What is a Monolithic Operating System?

2.1.

Advantages

2.1.1.

Fast

2.1.2.

Direct Interaction between Components

2.1.3.

Easy and Simple

2.1.4.

Better for Smaller Tasks

2.2.

Disadvantages

2.2.1.

Prone to Errors

2.2.2.

Difficult to Update

2.2.3.

Not Portable

What is a Layered Operating System?

3.1.

Layer-1: Hardware

3.2.

Layer-2: CPU Layer

3.3.

Layer-3: Memory Management

3.4.

Layer-4: Process Management

3.5.

Layer-5: Input-Output Buffer

3.6.

Layer-6: User Programs

Advantages

4.1.

Modularity

4.2.

Abstraction

4.3.

Easy Update

4.4.

Easy Debugging

Disadvantages

5.1.

Slower in Execution

5.2.

Complex Implementation

5.3.

Performance Degradation

Monolithic VS Layered Operating System

Frequently Asked Questions

7.1.

What is a microkernel?

7.2.

Is LINUX monolithic or layered?

7.3.

Are monolithic kernels faster?

Conclusion

Last Updated: Mar 27, 2024

Monolithic vs Layered OS

Author Apoorv Dixit

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Introduction

We all know that an operating system is the most important software that runs on a computer. It manages the computer's memory, processes, software, and hardware. It acts as the interface between the user and the computer system and helps the user to communicate with the computer. OS can be classified into many types based on its architecture. In this blog, we will discuss two important architectures: monolithic and layered OS. We will also see what these are and the key differences between them.

Also see, Multiprogramming vs Multitasking And Open Source Operating System

What is a Monolithic Operating System?

In this operating system, all the major components of the OS are located in the kernel space( it is a computer program at the core of OS). The kernel controls all the major features like memory management, process management, file management, and device management. It is a straightforward and vintage operating system that was first introduced in 1970. It was then used for small work like batch processing and time-sharing. Now let's discuss its architecture.

There are mainly three layers in a monolithic operating system: hardware, application, and monolithic kernel. As discussed above, the kernel handles the OS services like CPU scheduling, memory management, etc. The application requests services from the kernel; system calls do it. When an application requests a service hardware address space, the application switches to the hardware address of the OS; these operating systems also have a high-level virtual interface over computer hardware. Now let's discuss what its advantages and disadvantages are:

Advantages

Fast

Monolithic operating systems are fast. Thus, they provide better process scheduling, memory management, file management, etc.

Direct Interaction between Components

All the components and the kernel can directly interact. It also helps in gaining a better speed.

Easy and Simple

Its structure is easy and simple as all the components are located in the same address space.

Better for Smaller Tasks

Monolithic OS works better for handling smaller tasks.

Disadvantages

Prone to Errors

Monolithic OS can generate errors and bugs in the system. It is because user programs use the same address space as the kernel.

Difficult to Update

In monolithic OS, all the OS code is in a single big chunk; therefore, it is difficult to add or remove features in the OS.

Not Portable

The code written in monolithic OS is difficult to carry with or transfer to another system: this is because all the code works in a big chunk only, and you have to move it all.

You can also read about the Multilevel Feedback Queue Scheduling.

What is a Layered Operating System?

As the name suggests, a layered operating system is an operating system with multiple layers. In the layered operating system, all layers exist separately to perform certain functionality, and modification in one layer does not affect other layers. The layered architecture was developed to overcome the limitations of the monolithic operating system.

Since layered architecture is more modulated, it is easier to create and update.

There are mainly six main layers in layered operating systems. These are:

Layer-1: Hardware

It is the lowest layer in the operating system architecture. The layer handles the hardware devices, where all the hardware devices are installed.

Layer-2: CPU Layer

All the tasks and CPU processes are scheduled in this layer.

Layer-3: Memory Management

The layer handles memory. It moves processes from the disk(secondary storage) to primary memory for execution and returns executed processes to the disk. The layer helps to utilize memory efficiently.

Layer-4: Process Management

The layer assigns the CPU to execute processes.

Layer-5: Input-Output Buffer

The layer provides an I/O device buffer and ensures that all the input-output devices work in synchronization. It allows the user to interact with the system.

Layer-6: User Programs

It is the highest layer in a layered operating system, and it is associated with the user programs like word processors, browsers, etc.

Now let’s discuss certain advantages and disadvantages of the layered OS:

Advantages

Modularity

The layered architecture is modular; therefore, it is easy to debug and update. Changes made to one layer do not affect the other layers.

Abstraction

The functions and implementations of each layer are abstract to each other. One layer is not concerned with the working of other layers and provides necessary input or output to the neighboring layers hiding their own implementation of working.

Easy Update

The modular system is easier to update. Only the layered which needs the update is worked on, and related code is modified. This doesn’t affect other layers, and no changes are required there.

Easy Debugging

The discrete layers are quite easy to debug. If any sort of error occurs in the memory or scheduling layer, then the concerned layers can be debugged.

Disadvantages

Slower in Execution

Layered OS is slow compared to monolithic OS. When a request is sent from one layer to another, it must traverse all the layers between the two, which increases the response time.

Complex Implementation

The layered architecture is somewhat complex, where a layer can utilize the services of the layers below it. And the requested layer should be able to provide the requested services.

Performance Degradation

In layered OS, too many layers are present which degrades the performance of the system.

You can also read about the Multilevel Queue Scheduling.

Monolithic VS Layered Operating System

As we have discussed above, in monolithic OS architecture, the entire OS works in the kernel space, whereas in layered OS architecture, the operating system is divided into several independent layers having specific functionality. The differences can be summarized into two main points:

A monolithic OS is one complete operating system that operates in kernel space, whereas a layered OS is divided into several layers, each layer serving a specific task.
There are mainly three layers in a monolithic operating system, but a layered operating system has multiple layers(mainly six, we have discussed the six above in this article).

Parameter	Monolithic Operating System	Layered Operating System
Working	Complete operating system operating in kernel space.	The operating system is divided into several layers, each performing a specific task.
Number of Levels	Mainly, three layers are present.	Multiple layers are present in layered os.
Modularity	In monolithic OS, all the components and the kernel can directly interact, making it less modular.	The layered architecture is modular; therefore, it is easy to debug and update.
Modification and Updates	These are difficult to modify and update because all the code needs to be recompiled again after a minor update.	These are easier to update since the code of the concerned layer needs to be modified only.

Also see, Difference Between Structure and Union

Frequently Asked Questions

What is a microkernel?

A microkernel is one of the classifications of the kernel that manages all the system resources. It provides a bare minimum of the software to start an operating system. In this user and kernel, services are implemented in different address spaces.

Is LINUX monolithic or layered?

Linux and other UNIX systems are considered monolithic kernels. It is because all the functionalities are compiled into one big chunk of code.

Are monolithic kernels faster?

Monolithic kernels are much faster when compared to microkernels or other OS. It is because all the instructions run in the same address space, which makes the execution faster.

Conclusion

In this article, we have learned about monolithic and layered operating systems. We have discussed their architecture in detail and the layers which they have. We also discussed the main differences between the two in terms of functioning and architecture.