What is a Kernel in OS? What are the types of Kernel?

Every operating system- whether it is Windows, Mac, Linux, or Android, has a core program called a Kernel which acts as the ‘boss’ for the whole system. It is the heart of the OS! The Kernel is nothing but a computer program which controls everything else. Anything that happens on the computer goes through it. In this post, we will discuss what is a Kernel in an OS, and the different types of Kernels.

What is a Kernel in OS

Now that we know that its a core program in the OS, one should also know it is also the first program that loads after the bootloader. It then does all the talking between the hardware and the software or applications. So if you launch a program, the user interface sends a request to Kernel. The Kernel then sends a request to CPU, Memory to assign processing power, memory, and other things so the application can run smoothly in the front end.

You can imagine Kernel as a translator. It converts input/output requests from software into an instruction set for the CPU and GPU. In simple words, its a layer between the software and the hardware which makes everything possible. The kernel manages the following:

1. CPU/GPU
2. Memory
3. Input/Output or IO devices
4. Resource management
5. Memory management
6. Device management
7. System calls.

User processes can access kernel-space only through the use of system calls. If a program tries to access directly, it will result in a fault.

Kernel Security & Protection

The kernel also protects the hardware. If there is no protection, any program will be able to carry out any task on the computer, including crashing your computer, corrupting data, etc.

In modern-day computers, security is implemented on the hardware level. For example, Windows will not load drivers which are not from a trusted source and certified using signature. Secure Boot and Trusted Boot are classic examples.

Secure Boot: It is a security standard developed by members of the PC industry. It helps you protect your system from malicious programs by not allowing any unauthorized applications to run during the system start-up process. The feature makes sure that your PC boots using only software that is trusted by the PC manufacturer. So, whenever your PC starts, the firmware checks the signature of each piece of boot software, including firmware drivers (Option ROMs) and the operating system. If the signatures are verified, the PC boots and the firmware gives control to the operating system.

Trusted Boot: It uses the Virtual Trusted Platform Module (VTPM) to verify the digital signature of the Windows 10 kernel before loading it. In turn, it confirms every other component of the Windows startup process, including the boot drivers, startup files, and ELAM. If a file has been altered or changed to any extent, the bootloader detects it and refuses to load it by recognizing it as the corrupted component. In short, it provides a chain of trust for all the elements during boot.

What are the types of Kernel

The Kernel can also talk to hardware on a secure line. So companies can develop a Kernel which can talk to their hardware through a set of buttons. Take the washing machine for an example. Depending on the knobs you move, and time you set – a basic level of Kernel should be enough. That said, Kernel themselves grow complicated with time, which results in types of Kernel.

1. Monolithic Kernel: Here, the OS and Kernel both run in the same memory space and suitable where security is not a significant concern. It results in faster access, but if there is a bug in the device driver, the entire system crashes.
2. Microkernel: Its a stripped-down version of Monolithic Kernel where the Kernel itself can do most of the job done, and there is no need of an extra GUI. They should be used where security and the crashing system isn’t or will not happen.
3. Hybrid Kernel: This Kernel is what we see most. Windows, Apple’s macOS. They are a mix of Monolithic Kernel and Microkernel. It moves out drivers but keeps system services inside the Kernel – similar to how drivers are loaded when Windows Starts the bootup process.
4. Nano Kernel: If you need to have a kernel, but its majority of function is set up outside, then this comes into the picture.
5. Exo Kernel: This kernel only offers process protection and resource handling. However it is mostly used when you are testing out an inhouse project, and you upgrade to a better Kernel type.

There is a lot more to a Kernel than what we have talked about. As you dig deeper, the definition of Kernel gets broader and more profound.

We hope the post was easy to understand and helps you get through the basic.

What is kernel in windows operating system

Kernel is central component of an operating system that manages operations of computer and hardware. It basically manages operations of memory and CPU time. It is core component of an operating system. Kernel acts as a bridge between applications and data processing performed at hardware level using inter-process communication and system calls.

Kernel loads first into memory when an operating system is loaded and remains into memory until operating system is shut down again. It is responsible for various tasks such as disk management, task management, and memory management.

It decides which process should be allocated to processor to execute and which process should be kept in main memory to execute. It basically acts as an interface between user applications and hardware. The major aim of kernel is to manage communication between software i.e. user-level applications and hardware i.e., CPU and disk memory.

Objectives of Kernel :

• To establish communication between user level application and hardware.
• To decide state of incoming processes.
• To control disk management.
• To control memory management.
• To control task management.

Types of Kernel :

1. Monolithic Kernel –
It is one of types of kernel where all operating system services operate in kernel space. It has dependencies between systems components. It has huge lines of code which is complex.

Example :

• Advantage :
  It has good performance.
• Disadvantage :
  It has dependencies between system component and lines of code in millions.

2. Micro Kernel –
It is kernel types which has minimalist approach. It has virtual memory and thread scheduling. It is more stable with less services in kernel space. It puts rest in user space.

Example :

• Advantage :
  It is more stable.
• Disadvantage :
  There are lots of system calls and context switches.

3. Hybrid Kernel –
It is the combination of both monolithic kernel and mircrokernel. It has speed and design of monolithic kernel and modularity and stability of microkernel.

Example :

• Advantage :
  It combines both monolithic kernel and microkernel.
• Disadvantage :
  It is still similar to monolithic kernel.

4. Exo Kernel –
It is the type of kernel which follows end-to-end principle. It has fewest hardware abstractions as possible. It allocates physical resources to applications.

Example :

• Advantage :
  It has fewest hardware abstractions.
• Disadvantage :
  There is more work for application developers.

5. Nano Kernel –
It is the type of kernel that offers hardware abstraction but without system services. Micro Kernel also does not have system services therefore the Micro Kernel and Nano Kernel have become analogous.

Example :

• Advantage :
  It offers hardware abstractions without system services.
• Disadvantage :
  It is quite same as Micro kernel hence it is less used.

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What kind of kernel does MS Windows have?

I saw a question on Linux Kernel. While reading that I had this doubt.

3 Answers 3

The Windows NT branch of windows has a Hybrid Kernel. It’s neither a monolithic kernel where all services run in kernel mode or a Micro kernel where everything runs in user space. This provides a balance between the protection gained from a microkernel and the performance that can be seen in a monolithis kernel (as there are fewer user/kernel mode context switches).

As an example, device drivers and the Hardware Abstraction layer run in kernel node but the Workstation service runs in user mode. The wikipedia article on Hybrid Kernels has a good overview.

The Windows Internals book gives an explanation for the hybrid approach

. The Carnegie Mellon University Mach operating system, a contemporary example of a microkernel architecture, implements a minimal kernel that comprises thread scheduling, message passing, virtual memory, and device drivers. Everything else, including various APIs, file systems, and networking, runs in user mode. However, commercial implementations of the Mach microkernel operating system typically run at least all file system, networking, and memory management code in kernel mode. The reason is simple: the pure microkernel design is commercially impractical because it’s too inefficient.

What is an OS kernel ? How does it differ from an operating system? [closed]

Want to improve this question? Update the question so it’s on-topic for Stack Overflow.

Closed 8 years ago .

I am not able to understand the difference between a kernel and an operating system. I do not see any difference between them. Is the kernel an operating system?

11 Answers 11

The technical definition of an operating system is «a platform that consists of specific set of libraries and infrastructure for applications to be built upon and interact with each other». A kernel is an operating system in that sense.

The end-user definition is usually something around «a software package that provides a desktop, shortcuts to applications, a web browser and a media player». A kernel doesn’t match that definition.

So for an end-user a Linux distribution (say Ubuntu) is an Operating System while for a programmer the Linux kernel itself is a perfectly valid OS depending on what you’re trying to achieve. For instance embedded systems are mostly just kernel with very small number of specialized processes running on top of them. In that case the kernel itself becomes the OS itself.

I think you can draw the line at what the majority of the applications running on top of that OS do require. If most of them require only kernel, the kernel is the OS, if most of them require X Window System running, then your OS becomes X + kernel.

What is kernel in windows operating system

A Kernel is a computer program that is the heart and core of an Operating System. Since the Operating System has control over the system so, the Kernel also has control over everything in the system. It is the most important part of an Operating System. Whenever a system starts, the Kernel is the first program that is loaded after the bootloader because the Kernel has to handle the rest of the thing of the system for the Operating System. The Kernel remains in the memory until the Operating System is shut-down.

The Kernel is responsible for low-level tasks such as disk management, memory management, task management, etc. It provides an interface between the user and the hardware components of the system. When a process makes a request to the Kernel, then it is called System Call.

A Kernel is provided with a protected Kernel Space which is a separate area of memory and this area is not accessible by other application programs. So, the code of the Kernel is loaded into this protected Kernel Space. Apart from this, the memory used by other applications is called the User Space. As these are two different spaces in the memory, so communication between them is a bit slower.

Functions of a Kernel

Following are the functions of a Kernel:

• Access Computer resource: A Kernel can access various computer resources like the CPU, I/O devices and other resources. It acts as a bridge between the user and the resources of the system.
• Resource Management: It is the duty of a Kernel to share the resources between various process in such a way that there is uniform access to the resources by every process.
• Memory Management: Every process needs some memory space. So, memory must be allocated and deallocated for its execution. All these memory management is done by a Kernel.
• Device Management: The peripheral devices connected in the system are used by the processes. So, the allocation of these devices is managed by the Kernel.

Kernel Mode and User Mode

There are certain instructions that need to be executed by Kernel only. So, the CPU executes these instructions in the Kernel Mode only. For example, memory management should be done in Kernel-Mode only. While in the User Mode, the CPU executes the processes that are given by the user in the User Space.

Types of Kernel

In general, there are five types of Kernel. They are:

1. Monolithic Kernels

Monolithic Kernels are those Kernels where the user services and the kernel services are implemented in the same memory space i.e. different memory for user services and kernel services are not used in this case. By doing so, the size of the Kernel is increased and this, in turn, increases the size of the Operating System. As there is no separate User Space and Kernel Space, so the execution of the process will be faster in Monolithic Kernels.

• It provides CPU scheduling, memory scheduling, file management through System calls only.
• Execution of the process is fast because there is no separate memory space for user and kernel.

• If any service fails, then it leads to system failure.
• If new services are to be added then the entire Operating System needs to be modified.

A Microkernel is different from Monolithic kernel because in a Microkernel, the user services and kernel services are implemented into different spaces i.e. we use User Space and Kernel Space in case of Microkernels. As we are using User Space and Kernel Space separately, so it reduces the size of the Kernel and this, in turn, reduces the size of Operating System.

As we are using different spaces for user services and kernel service, so the communication between application and services is done with the help of message parsing and this, in turn, reduces the speed of execution.

• If new services are to be added then it can be easily added.

• Since we are using User Space and Kernel Space separately, so the communication between these can reduce the overall execution time.

3. Hybrid Kernel

A Hybrid Kernel is a combination of both Monolithic Kernel and Microkernel. It makes the use of the speed of Monolithic Kernel and the modularity of Microkernel.

Hybrid kernels are micro kernels that have some «non-essential» code in kernel-space in order for the code to run more quickly than it would be in user-space. So, some services such as network stack or filesystem are run in Kernel space to reduce the performance overhead, but still, it runs kernel code as servers in the user-space.

In a Nanokrnel, as the name suggests, the whole code of the kernel is very small i.e. the code executing in the privileged mode of the hardware is very small. The term nanokernel is used to describe a kernel that supports a nanosecond clock resolution.

Exokernel is an Operating System kernel that is developed by the MIT parallel and the Distributed Operating Systems group. Here in this type of kernel, the resource protection is separated from the management and this, in turn, results in allowing us to perform application-specific customization.

In the Exokernel, the idea is not to implement all the abstractions. But the idea is to impose as few abstractions as possible and by doing so the abstraction should be used only when needed. So, no force abstraction will be there in Exokernel and this is the feature that makes it different from a Monolithic Kernel and Microkernel. But the drawback of this is the complex design. The design of the Exokernel is very complex.

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