Difference between Microkernel and Monolithic Kernel

The microkernel and monolithic kernels are two types of kernels in the operating system. The kernel is the main part of the OS. As a result, the kernel's important code is stored in different memory spaces. The kernel is a crucial component because it maintains the proper functioning of the complete system. It manages hardware and processes, files handling, and several other functions.

In this article, you will learn about the microkernel and monolithic kernel. But before discussing the differences, you must know about the microkernel and monolithic kernel.

What is Microkernel?

The microkernel is a type of kernel that permits the customization of the OS. It is privileged and provides low-level address space management as well as Inter-Process Communication (IPC). Furthermore, OS functions like the virtual memory manager, file system, and CPU scheduler are built on top of the microkernel. Every service has its address space to make them secure. Moreover, every application has its address space. As a result, there is protection between applications, OS Services, and the kernel.

When an application requests a service from the OS services, the OS services communicate with one another in order to provide the requested service to the application. Inter-Process Communication (IPC) can assist in establishing this communication. Overall, microkernel-based operating systems offer a high level of extensibility. It is also possible to customize the operating system's services to meet the needs of the application.

Advantages and Disadvantages of Microkernel

There are various advantages and disadvantages of the microkernel. Some of the advantages and disadvantages of the microkernel are as follows:

Advantages

1. These are modular, and several modules may be modified, reloaded, replaced without modifying the kernel.
2. The architecture of the microkernel is small and isolated, but it may work better.
3. The Microkernel system is a versatile technique in which the APIs implemented by several servers may coexist.
4. The system can be expanded more easily because it may be added to the system application without interrupting the kernel.
5. It adds new features without recompiling.
6. When compared to monolithic systems, there are fewer system crashes.

Disadvantages

1. A context switch is required in the microkernel when the drivers are run as processes.
2. The microkernel system performance might be variable and cause issues.
3. Microkernel services are more expensive than in a traditional monolithic system.

What is Monolithic Kernel?

The monolithic kernel manages the system's resources between the system application and the system hardware. Unlike the microkernel, user and kernel services are run in the same address space. It increases the kernel size and also increases the size of the OS.

The monolithic kernel offers CPU scheduling, device management, file management, memory management, process management, and other OS services via the system calls. All of these components, including file management and memory management, are located within the kernel. The user and kernel services use the same address space, resulting in a fast-executing operating system. One drawback of this kernel is that if anyone process or service of the system fails, the complete system crashes. The entire operating system must be modified to add a new service to a monolithic kernel.

Advantages and Disadvantages of Monolithic Kernel

There are various advantages and disadvantages of the monolithic kernel. Some of the advantages and disadvantages of the monolithic kernel are as follows:

Advantages

1. The monolithic kernel runs quickly because of memory management, file management, process scheduling, etc.
2. All of the components may interact directly with each other's and also with the kernel.
3. It is a single huge process that executes completely within a single address space.
4. Its structures are easy and simple. The kernel contains all of the components required for processing.

Disadvantages

1. If the user needs to add a new service, the user requires to modify the complete operating system.
2. It isn't easy to port code written in the monolithic operating system.
3. If any of the services fails, the entire system fails.

Main Differences between the Microkernel and Monolithic Kernel

Here, you will learn the main differences between the Microkernel and Monolithic Kernel. Various differences between the Microkernel and Monolithic Kernel are as follows:

1. A microkernel is a kernel type that implements an operating system by providing methods, including low-level address space management, IPC, and thread management. On the other hand, a monolithic kernel is a type of kernel in which the complete OS runs in the kernel space.
2. The microkernel runs user and kernel services in different address spaces. On the other hand, the monolithic kernel runs both kernel and user services in the same address space. In microkernels, only essential processes like IPC, memory management, and scheduling take place in kernel space.
3. The execution of the microkernel is slower because communication between the system's application and hardware is established by message passing. On the other hand, the execution of the monolithic kernel is faster because the system call establishes the communication of the system's application and hardware.
4. Microkernels use the messaging queues to achieve IPC. On the other hand, monolithic kernels use sockets and signals to achieve IPC.
5. The microkernel size is small than the monolithic kernel because only the kernel services run in the kernel address space. On the other hand, the monolithic kernel size is larger because both user and kernel services run in the same address space.
6. The microkernels are more secure than the monolithic kernels because the operating system is unchanged if a service fails in a microkernel. On the other hand, if a service fails in a monolithic kernel, the entire system fails.
7. The microkernel is simple to extend as new services are added in user address space, which is separate from kernel space, and thus the kernel doesn't need to be updated. On the other hand, the complete kernel must be updated if a new service is used in a monolithic kernel.
8. Microkernel designing needs less code that leads to fewer errors. In contrast, the monolithic kernel requires more code that leads to more errors.

Head-to-head Comparison between the Microkernel and Monolithic Kernel

Here, you will learn the head-to-head comparison between the Microkernel and Monolithic Kernel. The main differences between the Microkernel and Monolithic Kernel are as follows:

Features	Microkernel	Monolithic Kernel
Definition	It is a kernel type that implements an operating system by providing low-level address space management, IPC, and thread management.	It is a type of kernel in which the complete operating system runs at the kernel speed.
Size	It is smaller in size.	It is bigger than the microkernel.
Speed	Its process execution is slower.	Its process execution is faster.
Basic	It implements kernel and user services in different address spaces.	It implements both user and kernel services in the same address space.
Security	It is more secure than the monolithic kernel.	It is less secure than the microkernel.
Stability	A single process failure does not affect other processes.	In a monolithic kernel, if a service fails, the entire system fails.
Extendible	It is easy to extend.	It is hard to extend.
Code	More code is necessary to write a microkernel.	Less code is necessary to write a monolithic kernel.
Inter-Process	Communication Microkernels use the messaging queues to achieve IPC.	The monolithic kernels use signals and sockets to achieve IPC.
Maintainability It is easily maintainable.	Maintenance takes extra time and resources.
Debug	It is easy to debug.	It is hard to debug.
Example	Symbian, L4Linux, K42, Mac OS X, PikeOS, HURD, etc.	Linux, BSDs, Solaris, OS-9, DOS, OpenVMS, etc.

Conclusion

Both kernel architectures have many benefits and limitations. So, there is no simple solution as to which is better and must be used. The goals and requirements should choose the kernel style. Other types of kernels have nanokernels, hybrid kernels, and exokernels.