Microkernel in Operating System: Architecture, Advantages
Nathaniel Brooks
⚡ Smart Summary
Microkernel is a minimal operating system core that keeps only essential functions—memory management, process scheduling, and inter-process communication—in kernel space, while device drivers, file servers, and other services run separately in user space.
Before we learn Microkernel, let’s understand:
What is Kernel?
A kernel is an important part of an OS that manages system resources. It also acts as a bridge between the software and hardware of the computer. It is one of the first programs which is loaded on start-up after the bootloader. The kernel is also responsible for offering secure access to the machine’s hardware for various programs. It also decides when and how long a certain application uses specific hardware.
What is Microkernel?
Microkernel is a software or code which contains the required minimum amount of functions, data, and features to implement an operating system. It provides a minimal number of mechanisms, which is good enough to run the most basic functions of an operating system. It allows other parts of the operating system to be implemented as it does not impose a lot of policies.
Microkernels and their user environments are usually implemented in the C++ or C programming languages with a little bit of assembly. However, other implementation languages are possible with some high-level coding.
What is a Monolithic Kernel?
A monolithic kernel runs all the basic system services like process management, memory management, I/O communication, and interrupt handling, file system, etc., in kernel space.
In this type of kernel approach, the entire operating system runs as a single program in kernel mode. The operating system is written as a collection of procedures that are linked together into a large executable binary program.
Microkernel Architecture
A microkernel is the most important part for correct implementation of an operating system. As you can see in the diagram below, the microkernel fulfills basic operations like memory, process scheduling mechanisms, and inter-process communication.
Microkernel Based Operating System
The microkernel is the only software executing at the privileged level. The other important functionalities of the OS are removed from kernel mode and run in user mode. These functionalities may be device drivers, applications, file servers, inter-process communication, etc.
Components of Microkernel
A microkernel comprises only the core functionalities of the system. A component is included in the microkernel only if putting it outside would interrupt the functionality of the system. All other non-essential components should be put in user mode.
The minimum functionalities required in the microkernel are:
- Memory management mechanisms like address spaces should be included in the microkernel. It also contains memory protection features.
- Processor scheduling mechanisms should contain process and thread schedulers.
- Inter-process communication manages the servers that run their own address spaces.
Difference Between Microkernel and Monolithic Kernel
| Parameters | Monolithic Kernel | Microkernel |
|---|---|---|
| Basic | It is a large process running in a single address space. | It can be broken down into separate processes called servers. |
| Code | In order to write a monolithic kernel, less code is required. | In order to write a microkernel, more code is required. |
| Security | If a service crashes, the whole system collapses in a monolithic kernel. | If a service crashes, it never affects the working of a microkernel. |
| Communication | It is a single static binary file. | Servers communicate through IPC. |
| Example | Linux, BSDs, Microsoft Windows (95, 98, Me), Solaris, OS-9, AIX, DOS, XTS-400, etc. | L4Linux, QNX, Symbian, K42, Mac OS X, Integrity, etc. |
Advantages of Microkernel
Here are the pros/benefits of using a microkernel:
- Microkernel architecture is small and isolated, therefore it can function better.
- Microkernels are secure because only those components are included that would otherwise disrupt the functionality of the system.
- The expansion of the system is more accessible, so it can be added to the system application without disturbing the kernel.
- Microkernels are modular, and the different modules can be replaced, reloaded, or modified without even touching the kernel.
- Fewer system crashes when compared with monolithic systems.
- The microkernel interface helps you to enforce a more modular system structure.
- New features can be added without recompiling.
- Server malfunction is also isolated, just like any other user program’s malfunction.
- The microkernel system is flexible, so different strategies and APIs implemented by different servers can coexist in the system.
- Increased security and stability result from a decreased amount of code running in kernel mode.
Disadvantages of Microkernel
Here are the drawbacks/cons of using a microkernel:
- Providing services in a microkernel system is expensive compared to a normal monolithic system.
- A context switch or a function call is needed when the drivers are implemented as procedures or processes, respectively.
- The performance of a microkernel system can be indifferent and may lead to some problems.
