Difference Between Monolithic and Layered Operating Systems

The operating system is the primary platform on top of all the other programs and applications and serves as the medium for the user to communicate with the computer systems. The system structure is a crucial aspect of the functioning of the Operating Systems like monolithic and layered determines how different tasks are processed and the output is printed for them.

Introduction

To begin with, there is a simple fundamental structure called a Monolithic Operating System which only includes a few complex layers, and all the tasks are processed in one place. But there are complex structures to make the OS functions more organized. One such widely used structure is the Layered Operating System. Both approaches and their details are discussed in detail in the upcoming sections.

What is the Monolithic Operating System?

The Monolithic Operating Systems were first introduced in the 1970s as an elementary structured OS where the kernel directly controls all the basic tasks. These tasks include: 

• File management 
• Memory management 
• Device management 
• Process management 

These Monolithic systems are characterized by Monolithic Kernels, as these systems have a single kernel processing all kinds of tasks. 

There are three layers in a monolithic OS: hardware, application, and monolithic kernel. 

The Monolithic Design has no significant arrangement for an OS’s particular function. In some cases, the procedure may be separated, but essentially, they exist in the same kernel. Hence, adding special authorization or privilege to any particular function partition becomes difficult. 

Another key feature is the relatively low delay due to communication time taken by different parts of the kernel as they are located close. Hence, they can quickly transfer the required information. Although this system is efficient in terms of delay, it exposes the system to various risks and factors that lead to complete system failure.  

In the next section, we will discuss the advantages and disadvantages of the OS’s monolithic structure. 

Advantages of Monolithic Operating System

• Provides Speed: Faster as all the tasks are performed at the same place inside the memory. 
• Execution Inside Kernel: Complete execution occurs inside the monolithic kernel, a static binary file. 
• Structure: Straightforward structure. 

Disadvantages of Monolithic Operating System  

• Single Point Failure: Risk of Single Point Failure exists as everything happens in the kernel. The complete system will be disrupted if any function in the kernel is disrupted. 
• Difficulty in Adding Programs: Adding a new program requires the user to tweak the entire system. 

Example of a Monolithic Operating System 

Based on the above pros and cons of this structure, the following are the most common examples of the Monolithic Structure: 

• OS-9 OpenVMS 
•  Linux 
•  BSD 
•  SunOS 
•  AIX 
• MULTICS 

All these systems were built to enhance the benefits of this structure and use them for a particular use case.

Structuring an Operating System: Layered Approach

Introduction to Layered Approach

A proper hardware system backing the OS can be divided into compartments, leading to better functioning with fair task distribution. Such a system with layers on top of hardware and each layer handling a different set of tasks is referred to as the layered structure of the OS. 

As illustrated in the diagram following the basic hardware, multiple layers of different services are created. Finally, the last layer represents the user interface from where the user gives commands for the system. 

In such a system, if Layer n has to interact with Layer 1, the response will travel through all the layers until the end layer. The key in such a system is that all the layer below a particular layer has all the necessary functions inside of them to support the above ones.  

In modern systems where the layered structure is followed, precisely six essential layers are built on top of the hardware. These layers are: 

• Hardware: It is the innermost core and the layer on which all the other layers are built. This is the layer where all the hardware components are managed. 
• CPU Layer: This is where all the tasks are allocated to the CPU to process. 
• Memory: The layer on top of the CPU is the Memory. All the functions performed or performed by the CPU are stored here. Based on the status of the process, it is moved from temporary to permanent memory and back and forth. 
• Process Management: As the modern OS is multitasking, multiple tasks need CPU attention at a given time. This process manager manages the CPU’s attention and tasks simultaneously, which unbiasedly allocates CPU time to the tasks. 
• I/O Buffer: This is the layer where the User inputs and the outputs to be displayed to the user are temporarily stored. As both the input and output are tedious, time-consuming processes, a separate buffer helps in efficient CPU and memory management. 
•  User Interface: The last layer is in direct contact with the user and using which the user interacts with the system. 

Diagram of Layered Approach

Advantages of the Layered Approach

This structure is commonly used due to its multiple advantages to the system and its operations. Following are a few of its key benefits: 

• Updating the System: Functions of a particular layer can easily be modified without disturbing the functioning and system of the others. 
• Resolving Bugs: It is straightforward to solve the various bugs that might come as the error in a particular function directs us to the layer with an issue, and we only need to debug that layer. 
• Hardware Protection: Since fewer tasks have direct access to the hardware, it is not at risk. 

Disadvantages of the Layered Approach

The Layered approach, although it has a lot of benefits but comes with its own set of disadvantages: 

• Complex Architecture: The complex, layered structure is challenging to implement and organize and needs a lot of technical knowledge. 
• Execution Delay: As every response goes through all the layers, the execution of tasks can often become tiresome and delayed.

Example of Layered Approach

The Windows-NT is a commonly known example of the Layered OS approach. Windows Vista and Windows XP are some commonly used operating systems that the readers might have experienced from the Windows-NT family. This operating system has two modes of utilization – the user mode, which provides restricted access to the hardware resources and requires interaction with the hardware with the help of drivers, and the kernel mode, which does not have such restrictions and offers complete control over the hardware resources.

Difference between Monolithic and Layered Operating Systems

Monolithic Operating System	Layered Operating System
The Monolithic OS contains all the features inside its Monolithic Kernel.	In contrast, the Layered Architecture has several layers, each having specific functionalities to perform individually.
The whole Monolithic OS functionalities occur in the kernel itself.	This is not the case in a layered approach.
The number of layers is fixed to three for the monolithic OS.	The number of layers is usually six in the layered approach.
In the Monolithic Approach, all the components are situated at one address. Hence, they can directly interact with each other leading to lesser modularity.	In the layered approach, updating and debugging is more accessible as the functions are abstract. The code of a particular layer needs to be modified only.

Direct Comparison of Monolithic and Layered Operating Systems 

Following is a brief difference map between the two structures: 

Monolithic	Layered
Complete OS functions inside the kernel space itself.	OS functions are divided into multiple layers.
It consists of a total of three layers.	It consists of multiple layers which cannot be allotted a fixed number.
Components interact directly with one another.	Components do not interact directly with one another.
Lesser modularity.	More modularity.
Debugging and modification are less accessible.	Debugging and modification are more accessible.

Conclusion

This article briefly discussed the features, advantages, and disadvantages of the two famous OS structuring approaches, the Monolithic system, and the layered approach. Following the detailed understanding of the monolithic and layered operating system structures, we saw how they exist compared to one another. Finally, we understood that both have their own set of advantages and utilities. . Readers are encouraged to take notes of their most important findings from this article and visit them time and again to keep their memory refreshed about the fundamental structures of operating systems.

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FAQs

How do monolithic operating systems differ from layered operating systems? 

The monolithic and the layered approach of the OS structure can be differentiated based on two significant differences. One is that in a Monolithic, every task is performed, and every system is inside the kernel. Second, the monolithic has precisely three layers, and the Layered OS has multiple layers with different tasks allotted to other layers. 

Which Operating System is Better, Monolithic or Layered? 

Both Systems have their own set of pros and cons. The Monolithic system can be helpful when small tasks need to be performed, and quick processing is necessary. In contrast, the Layered Structure is suitable for situations where complex tasks need to be completed and abstraction is required as the number of functions needed is higher. 

Do you prefer a monolithic or layered operating system? 

In the present-day scenario where multitasking is necessary, the downtime should be zero. Therefore, it is better to use the Layered Approach for a better experience and to keep the system error-free. 

Operating systems can be monolithic or layered. Which is better? 

Both the system structures have their advantages, and based on the requirements, the suitable one can be selected. For example, if the task has minimalistic requirements and a fast output is a focus, then the monolithic OS can be a good option; on the other hand, layered can be helpful when a complex task with multiple functional requirements is at hand.