[Day 6] 2. Types of Kernel

1. Monolithic Kernel

A monolithic kernel is an operating system architecture where the entire kernel operates as a single large program in memory. It handles key tasks such as file management, device drivers, memory management, and system calls, all directly in kernel space.

• Imagine the OS as a team: In a monolithic kernel, the team works together in one big room without dividing tasks into separate areas.
• This enables faster communication between tasks, but fixing issues or adding features becomes more complicated due to tight integration.

In technical terms:

• Copy

  .c

  files → compiled into
  Copy

  .o

  files (object files)
• Copy

  .o

  files → linked into a single executable binary file, which is the kernel.

!2. Monolithic.png

Example: UNIX

2. Micro kernel

A micro kernel architecture keeps only essential functions in the kernel, such as basic process management and inter-process communication (IPC). Other components, like device drivers, file systems, and network management, run in user space as separate processes.

• Think of the micro kernel as a small control centre for critical tasks, with most work being handled by "external workers."
• This modular structure improves maintainability and security, though communication between components is slower.

!2. Micro.png

Monolithic vs. Microkernel:

• Monolithic: Faster, but harder to maintain. If one component fails, the entire kernel can crash.
• Microkernel: Slower, but more stable and easier to maintain. One failure doesn't bring down the whole system.

Examples: Symbian, MACH

3. Modular Kernel

A modular kernel is a hybrid of monolithic and microkernel architectures. It uses dynamically loadable modules, meaning only essential parts of the kernel load at startup. Additional modules load at runtime when needed.

• Faster than a microkernel but slower than a monolithic kernel.
• Easier to maintain with no need for IPC. However, if one module fails, the whole kernel can still crash.

!3. Modular.png

Example: Windows

Linux Kernel

The Linux Kernel is a combination of monolithic, micro, and modular kernel architectures, making it highly versatile.

Static Components

• Kernel (vmlinuz) located in

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  /boot/

  , containing features required at all times.

  Functions include:

  • Process Management
  • CPU Scheduling
  • Memory Management
  • IO Management
  • File Management
  • Hardware Abstraction
  • System Calls

Dynamic Components

• Dynamically loadable modules loaded into RAM only when needed during runtime.

  Examples:

  • File System Managers: FAT, NTFS, ZFS
  • Device Drivers

• These modules are called kernel objects with the extension

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  .ko

  .

• Location: /lib/modules/ `uname -r`

Note: mac OS uses a hybrid kernel like Linux, combining MACH and UNIX. The kernel is named Darwin.

For Linux kernel source code, visit kernel.org.