Unix - kernel in unix

1. What is a Kernel?

The kernel is the core component of any operating system (Linux, Unix, Windows, etc.).
It acts as a bridge between hardware and software.

In Linux/Unix, the kernel is responsible for:

  • Managing system resources (CPU, memory, I/O devices).

  • Handling system calls (requests from applications).

  • Providing abstraction so applications don’t directly deal with hardware.

Think of it as the “heart” of the operating system.

2. Functions of the Kernel in Linux/Unix

  1. Process Management

    • Creates, schedules, and terminates processes.

    • Example: Running ps -aux in Linux lists all running processes.

  2. Memory Management

    • Allocates/deallocates memory to processes.

    • Manages virtual memory and paging.

  3. Device Management

    • Provides drivers so applications can use hardware (disk, keyboard, printer).

    • Example: /dev/sda represents a storage device.

  4. File System Management

    • Provides a way to read/write files.

    • Example: Linux uses ext4, xfs, etc.

  5. System Calls Interface

    • Provides APIs that applications use to interact with the kernel.

    • Example: open(), read(), write() system calls.

3. Example

Suppose you run the command:

cat file.txt

Here’s what happens:

  1. Shell sends request to kernel to open file.txt.

  2. Kernel looks up the file in the file system.

  3. Kernel asks disk driver (hardware) to fetch the data.

  4. Kernel passes data back to the shell.

  5. Shell displays content on your terminal.

You didn’t need to write instructions for disk hardware — kernel handled it!

4. Visual Diagram of Kernel in Linux/Unix

Here’s a simple layered diagram:

+---------------------------------------------------+
|                 User Applications                 |
|   (Shell, Browsers, Editors, Compilers, etc.)     |
+---------------------------------------------------+
|             System Call Interface (API)           |
+---------------------------------------------------+
|                     Kernel                        |
|   - Process Management                            |
|   - Memory Management                             |
|   - File System Management                        |
|   - Device Drivers                                |
|   - Networking                                    |
+---------------------------------------------------+
|                 Hardware (CPU, RAM, I/O)          |
+---------------------------------------------------+

5. Types of Kernels

  • Monolithic Kernel (Linux, traditional Unix)

    • All OS services run in kernel space.

    • Faster, but large in size.

  • Microkernel (Minix, QNX)

    • Only essential parts (CPU, memory, IPC) in kernel space.

    • Other services run in user space (safer, but slower).

Linux uses a Monolithic Kernel, but with modular support (drivers can be loaded/unloaded at runtime using modprobe).

In summary:
The Linux/Unix kernel is the core program that manages hardware resources, allows multiple processes to run, and provides a safe interface for applications. Without the kernel, applications cannot run or interact with hardware.