MenuetOS KolibriOS: A Non-POSIX Operating System Built in Assembly
Source: Dev.to
What This Operating System Is
MenuetOS is a standalone operating system written almost entirely in x86 assembly.
KolibriOS is a continuation of the same design after MenuetOS development slowed, keeping the system alive and actively maintained.
Together, they represent a single OS lineage with these characteristics:
- native graphical desktop
- preemptive multitasking
- basic networking
- custom system APIs
- no Unix or Linux components
They are not Linux distributions, do not reuse Unix userland, and do not depend on POSIX.
Why MenuetOS and KolibriOS Exist
Most modern OS design assumes:
- abstraction is cheap
- memory is plentiful
- safety must be layered on
MenuetOS exists because its creator wanted to answer a different question: how small can a usable operating system actually be?
KolibriOS continues this idea by keeping the system practical while preserving the original philosophy.
These operating systems exist to show that:
- graphical systems do not need millions of lines of code
- multitasking does not require heavy runtimes
- modern hardware often hides waste behind abstraction
Kernel
MenuetOS and KolibriOS use a custom monolithic kernel written largely in assembly. The kernel is responsible for:
- task scheduling
- memory management
- basic hardware access
- system calls for applications
There is very little abstraction between the kernel and the hardware. The kernel is intentionally small, direct, and predictable, which improves performance and simplicity but reduces portability.
POSIX Status
MenuetOS and KolibriOS are explicitly non‑POSIX. They do not provide:
- POSIX system calls
fork/execprocess model- Unix signals
- Unix permissions
- POSIX shells or utilities
This is intentional. POSIX assumes unsafe C‑style programming and compatibility over minimalism, whereas these operating systems assume:
- explicit control
- minimal overhead
- purpose‑built APIs
Processor Architecture
Both operating systems target the x86 architecture (primarily 32‑bit with limited 64‑bit support). This narrow focus allows:
- direct CPU feature usage
- predictable interrupt handling
- extremely small system size
Portability to ARM or other architectures is not a goal; efficiency on x86 is.
File System
MenuetOS and KolibriOS use simple custom filesystems. Design priorities include:
- minimal metadata
- low overhead
- fast access
- easy implementation
They are not designed for:
- journaling
- enterprise reliability
- large storage arrays
- complex permission models
The filesystem exists to support the OS, not to act as a general storage platform.
Hardware Requirements
These operating systems have extremely low hardware requirements.
Typical expectations:
- CPU: older x86 processors
- RAM: tens of megabytes
- Storage: very small disk footprint
- Graphics: basic framebuffer support
They run comfortably on:
- old PCs
- virtual machines
- minimal hardware setups
This makes them suitable for hardware reuse and low‑resource environments.
Who Should Use MenuetOS or KolibriOS
These operating systems make sense for people who:
- study low‑level OS design
- want to understand systems without abstraction layers
- care about performance per line of code
- work close to hardware
- want to reuse old x86 machines
They are especially useful as:
- learning platforms
- reference systems
- experimentation environments
Where They Do Not Make Sense
MenuetOS and KolibriOS are not suitable for:
- modern desktop workflows
- gaming
- enterprise systems
- security‑critical environments
- POSIX‑dependent software
They intentionally trade compatibility and safety layers for simplicity.
MenuetOS and KolibriOS remain relevant because they demonstrate that complexity is optional. They do not argue against modern operating systems; they simply prove that a small, explicit, non‑POSIX OS can still exist and work today.