Overview of Monolithic kernel vs Microkernel (μ-kernel)
The following article provides a difference between Monolithic kernel vs Microkernel. Let’s see first what is Kernel? In today’s world, we are all dependent on computers and mobile devices and use them in our day to day lives. Have you ever wondered how these tiny devices work internally? Have you ever tried understanding an operating system and happen to come across the term “kernel” and wonder what it is or where did it come from? Ever used a mouse for the first time and been amused with how the computer recognizes your mouse movement? That’s where the Kernel comes into play.
A kernel is a software that forms a layer between the hardware and the operating system. It is the first program to get loaded on system start-up. It manages memory resources, CPU resources, and all processes/ tasks on any computer. All requests to other resources go through the kernel. If we want to print, the print instruction is processed through the kernel.
Every click of our mouse is processed through the kernel. If a process requires memory to execute, it will be the kernel that is allocating the memory. It is at the center of every operation being executed by your computer. It is responsible for memory management, networking, device control, file systems to name a few. Every computer system uses a kernel. All operating systems such as Windows, Mac OS, Linux use kernel. It’s not just limited to computers, even your mobile device operating systems such as Android, Windows mobile and iOS use kernel.
How does Kernel differ from an Operating System?
A kernel is part of an operating system or you could say it the heart of an operating system. A kernel put together with useful applications becomes an operating system.
The important thing to note here is that an operating system consists of two parts:
- The kernel space (privileged mode)
- The userspace (unprivileged mode)
There are different types of the kernel. The two main types are namely:
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- Monolithic kernel
- MicroKernel
These types of the kernel are segregated based on how they manage a request from a process (also known as system calls) and resources. Monolithic kernels are much older than microkernels. Microkernels were discovered in the late 1980s.
Head to Head Comparison between Monolithic Kernel vs MicroKernel
Below are the top 10 differences between Monolithic Kernel vs MicroKernel
Key Differences between Monolithic Kernel vs MicroKernel
Let us discuss some of the major differences between Monolithic Kernel vs MicroKernel.
- Space usage for execution: Monolithic kernel runs all the operating system instructions in the same address space that is the kernel space, whereas Microkernel runs the majority of system instructions in userspace and only a few in kernel space. That is in the case of microkernels only important processes such as interprocess communication, scheduling, and memory management take place in kernel space.
- Size of the kernel: In Monolithic since all system instructions are executed under kernel space it increases the overall size of the kernel. This leads to an increase in the size of the operating system as well.
- Speed of Execution: Monolithic kernel provides better speed when compared to Microkernel as it runs all instructions under the same address space, which makes execution faster. In the case of Microkernel, the execution is slower due to additional messages passing between the different services running in different address spaces.
- Stability: If a process crashes in a monolithic kernel, it results in a system-wide halt. This is because every process running in the same address space is affected. Whereas in the case of microkernel due to the division of system operation between kernel and userspace, a service crash does not affect other services.
- Interprocess communication: Monolithic kernels make use of signals and sockets to achieve interprocess communication whereas micro kernels make use of messaging queues to achieve the same.
- Extensibility: One of the major differences between the two kernel types is extensibility. For adding new features to a monolithic kernel, one would have to recompile the whole kernel. Recompilation would lead to more memory and time consumption. On the other hand in the case of the microkernel, the services are isolated from each other as it implements messaging queues, making it more flexible to add or remove features.
- Maintainability: This is similar to extensibility. In order to fix any bugs in the monolithic kernel, one would have to recompile the entire kernel. Whereas that is not the case for microkernel.
- Debug: A crash in the privileged mode that is kernel space could corrupt the debugger itself. Due to this, it’s difficult to debug a monolithic kernel when compared to a microkernel.
- Security: Microkernels are more secure as compared to monolithic kernel since monolithic kernel runs their entire code in privileged mode increasing the chances of a disaster.
Monolithic Kernel vs Microkernel Comparison Table
Let us discuss the topmost differences between Monolithic Kernel vs MicroKernel.
| Basis of Comparison between Monolithic Kernel vs MicroKernel | Monolithic Kernel | MicroKernel |
| Execution Style | All processes are executed under the kernel space in privileged mode. | Only the most important processes take place in the Kernel space. All other processes are executed in the user space. |
| Size | Kernel size is bigger when compared to Microkernel. | Kernel size is smaller with respect to the monolithic kernel. |
| Speed | It provides faster execution of processes. | Process execution is slower. |
| Stability | A single process crash will cause the entire system to crash. | A single process crash will have no impact on other processes. |
| Inter-Process Communication | Use signals and sockets to achieve interprocess communication. | Use messaging queues to achieve inter process communication. |
| Extensibility | Difficult to extend. | Easily extensible. |
| Maintainability | Maintenance is more time and resource consuming. | Easily maintainable |
| Debug | Harder to debug | Easier to debug |
| Security | Less Secure. | More Secure |
| Example | Linux | Mac OS |
Conclusion
Both the kernel architectures come with their own set of pros and cons. Therefore there is not a straight forward answer as to which one is better and should be used. The kernel style should be selected based on the needs and requirements one has to meet. A few other types of kernels are the hybrid kernel, nanokernel, exokernel.
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