---
tags:
  - operating-systems
  - linux
---

# Basic model of a \*nix operating system

We can abstract the Linux OS into three operational levels or tiers, from the
bottom up:

- **User processes: user space**
  - The running programs that the kernel manages. Also known as the user space
    which is the memory that the kernel assigns for user processes. Comprising:
    - Graphical user interface
    - Servers
    - Shell

- **Kernel: kernel space**
  - The core of the operating system. Software residing in memory that tells the
    CPU where to look for its next task. Acts as a mediator and primary
    interface between the hardware and the user processes. Known as kernel
    space: the memory that the kernel allocates for itself. Comprising:
    - System calls
    - Process management
    - Memory management
    - Device drivers

- **Hardware**
  - The base: one or more CPUs and RAM memory performing computations and
    writing to memory. Comprising:
    - Processor (CPU)
    - Main memory (RAM)
    - Disks
    - Network ports