- - Kernel: The kernel is the core of the operating system that controls the basic functions of the system, such as process management, memory management, device management, and system calls.
- - Bootloader: The bootloader is a small program that runs when the computer is turned on and loads the kernel into memory and executes it.
- - Shell: The shell is a program that provides a user interface to interact with the operating system, such as typing commands and running programs.
The operating system can be implemented with the help of various structures. The structure of the OS depends mainly on how the various standard components of the operating system are interconnected and melded into the kernel. A design known as an operating system enables user application programs to communicate with the machine’s hardware. Given its complex design and need to be easy to use and modify, the operating system should be constructed with the utmost care. A straightforward way to do this is to supernaturally develop the operating system. These parts must each have unique inputs, outputs, and functionalities.
In this blog post, we will compare and contrast some of the most popular and widely used operating system architectures, based on the following criteria:- Performance and efficiency
- Simplicity and modularity
- Reliability and security
- Portability and compatibility
We will also provide some examples of operating systems that use each architecture, as well as some resources and tools for learning and using them.
Operating System Architectures
Monolithic Kernel
A monolithic kernel is an operating system architecture that implements all the components and services of the operating system in a single kernel. The kernel runs in the privileged mode of the processor and has direct access to the hardware and the system resources. The user applications run in the user mode of the processor and communicate with the kernel through system calls.
Some examples of operating systems that use a monolithic kernel are Linux, Windows, and macOS.
Pros:- High performance and efficiency, as the kernel can execute the system functions without switching modes or contexts.
- Simplicity and reliability, as the kernel is a single unit that can be tested and verified easily.
- Security and portability, as the kernel can control and protect the hardware and the system resources from unauthorized access or modification.
- Large size and complexity, as the kernel contains all the components and services of the operating system, which makes it difficult to maintain and debug.
- Lack of modularity, as the kernel is a single unit that cannot be modified or extended easily without recompiling the whole kernel.
- - [Monolithic Kernel]: A comprehensive and beginner-friendly tutorial on monolithic kernel.
- - [Linux]: The official website for Linux, with documentation, guides, tutorials, courses, and more.
- - [Windows]: The official website for Windows, with documentation, guides, tutorials, courses, and more.
- - [macOS]: The official website for macOS, with documentation, guides, tutorials, courses, and more.
Microkernel
A microkernel is an operating system architecture that implements only the essential components and services of the operating system in a small kernel. The kernel runs in the privileged mode of the processor and provides the basic functions of the system, such as process management, memory management, inter-process communication, and system calls. The other components and services of the operating system, such as device drivers, file systems, network protocols, and user interfaces, are implemented as separate modules or processes that run in the user mode of the processor and communicate with the kernel and each other through message passing.
Some examples of operating systems that use a microkernel are QNX, Minix, and Hurd. Pros:- Small size and modularity, as the kernel contains only the essential components and services of the operating system, which makes it easy to maintain and extend.
- Flexibility and functionality, as the other components and services of the operating system can be added, removed, or modified without affecting the kernel.
- Ease of maintenance and debugging, as the kernel and the other components and services of the operating system can be tested and verified independently.
- Fault tolerance and security, as the kernel and the other components and services of the operating system are isolated from each other and can be recovered or replaced in case of failure or attack.
- Low performance and efficiency, as the kernel and the other components and services of the operating system have to switch modes and contexts and exchange messages frequently, which causes overhead and latency.
- Complexity and difficulty of implementation, as the kernel and the other components and services of the operating system have to coordinate and synchronize with each other through message passing, which requires careful design and programming.
- - [Microkernel]: A comprehensive and beginner-friendly tutorial on microkernel.
- - [QNX]: The official website for QNX, with documentation, guides, tutorials, courses, and more.
- - [Minix]: The official website for Minix, with documentation, guides, tutorials, courses, and more.
- - [Hurd]: The official website for Hurd, with documentation, guides, tutorials, courses, and more.
Hybrid Kernel
A hybrid kernel is an operating system architecture that combines the features and benefits of both the monolithic kernel and the microkernel. The kernel runs in the privileged mode of the processor and provides the essential functions of the system, such as process management, memory management, inter-process communication, and system calls. The other components and services of the operating system, such as device drivers, file systems, network protocols, and user interfaces, are implemented as either modules that run in the kernel mode or processes that run in the user mode, depending on their performance and security requirements. The kernel and the other components and services of the operating system communicate with each other through either direct function calls or message passing, depending on their mode and location.
Some examples of operating systems that use a hybrid kernel are Windows NT, macOS X, and Solaris. Pros:- Improved performance and compatibility, as the kernel and the other components and services of the operating system can execute the system functions without switching modes or contexts, or use message passing to reduce the overhead and latency, depending on their needs and preferences.
- Enhanced functionality and security, as the kernel and the other components and services of the operating system can access the hardware and the system resources directly, or use message passing to isolate and protect them from unauthorized access or modification, depending on their needs and preferences.
- Increased size and complexity, as the kernel and the other components and services of the operating system contain both the monolithic and the microkernel features, which makes it difficult to maintain and debug.
- Inconsistency and ambiguity, as the kernel and the other components and services of the operating system have different modes, locations, and communication methods, which makes it hard to define and verify their roles and responsibilities.
- - [Hybrid Kernel]: A comprehensive and beginner-friendly tutorial on hybrid kernel from GeeksforGeeks.
- - [Windows NT]: The official website for Windows NT, with documentation, guides, tutorials, courses, and more.
- - [macOS X]: The official website for macOS X, with documentation, guides, tutorials, courses, and more.
- - [Solaris]: The official website for Solaris, with documentation, guides, tutorials, courses, and more.
Exokernel
An exokernel is an operating system architecture that implements only the minimal components and services of the operating system in a small kernel. The kernel runs in the privileged mode of the processor and provides the basic functions of the system, such as memory allocation, process creation, and system calls. The other components and services of the operating system, such as device drivers, file systems, network protocols, and user interfaces, are implemented as separate libraries or applications that run in the user mode of the processor and communicate with the kernel and each other through system calls. The kernel does not abstract or manage the hardware and the system resources, but instead exposes them to the user applications, which can access and control them directly.
Some examples of operating systems that use an exokernel are ExOS, Aegis, and Xok. Pros:- High performance and efficiency, as the kernel and the user applications can access and control the hardware and the system resources directly, without any overhead or interference from the kernel.
- Flexibility and customizability, as the user applications can choose and implement their own components and services of the operating system, according to their needs and preferences.
- Low security and stability, as the kernel and the user applications can access and control the hardware and the system resources directly, without any protection or supervision from the kernel.
- Difficulty and complexity of implementation, as the user applications have to implement their own components and services of the operating system, which requires advanced knowledge and skills of the hardware and the system resources.
- - [Exokernel]: A comprehensive and beginner-friendly tutorial on exokernel from GeeksforGeeks.
- - [ExOS]: The official website for ExOS, with documentation, guides, tutorials, courses, and more.
- - [Aegis]: The official website for Aegis, with documentation, guides, tutorials, courses, and more.
- - [Xok]: The official website for Xok, with documentation, guides, tutorials, courses, and more.
Nanokernel
A nanokernel is an operating system architecture that implements only the most basic and essential components and services.
Source: (1) Different Approaches or Structures of Operating Systems. https://www.geeksforgeeks.org/different-approaches-or-structures-of-operating-systems/. (2) Different Types of Operating System [Pros and Cons] - KnowledgeHut. https://www.knowledgehut.com/blog/web-development/types-of-operating-system. (3) Types of Operating Systems : Architecture, Overview and Benefits - ElProCus. https://www.elprocus.com/different-types-of-computer-operating-systems/. (4) en.wikipedia.org. https://en.wikipedia.org/wiki/Operating_system.