MINI-OS

Currently, MINI-OS is a very small x86 32-bit pure assembly operating system.

MINI-OS supports running ANSI C90 C programs with dynamic memory allocation (malloc/free) and standard library support, excluding floating-point operations (float/double).

Note

MINI-OS is only an experimental system and is far from perfect.

Thanks to Gemini, Gork, GPT, and Mistral for their support.

The documentation and some comments were written by Gemini and GPT. A small part of the code was developed in collaboration with Gemini and GPT.

(Use QEMU)

👉 Flowchart

Current Features

• BIOS boot sector loader with kernel load to memory
• Protected-mode kernel entry ([org 0x8000])
• VGA text console and polling keyboard input
• ATA PIO disk I/O (LBA28, sector read/write)
• Custom filesystem with persistent directory tree
• IDT Interrupt Table & int 0x80 System Call Engine (sys_exit, sys_read, sys_write, sys_brk)
• Executable loader (run <file>) for multi-sector flat binaries at 0x00040000
• C90 application runtime with Dynamic Memory Allocation (malloc/free/realloc/calloc)
• ANSI C90 standard headers (<stdio.h>, <stdlib.h>, <string.h>, <ctype.h>, <limits.h>, <stddef.h>, <assert.h>)
• Host-side disk transport tool (tools/inject_transport.c) for inject /transport/ files
• Built-in shell commands: help, ls, pwd, cd, mkdir, touch, cat, edit, rm, mv, run <file>, format

Project Layout

• OS_src/boot/: bootloader sources
• OS_src/kernel/: kernel, shell, drivers, filesystem, IDT & syscalls, and utilities
• tools/: host build tools (inject_transport.c, elf2bin.c)
• transport/: host files injected into /transport/ on disk image
  • transport/lib/: C90 runtime library, crt0.asm, and standard C header wrappers
  • transport/apps/: user C applications (hello.c, calc.c, guess.c, banner.c)
  • transport/lib_test/: dedicated C library test suites (test_string.c, test_heap.c)
  • transport/build/: compiled flat output binaries (apps/*.bin, lib_test/*.bin)
• docs/: project documentation
• build/: generated kernel binaries and disk image

Requirements

• nasm
• cc / clang / gcc (host C compiler for inject_transport build)
• qemu-system-i386
• standard shell tools used by Makefile (dd, wc, mkdir, rm)

Build and Run

make clean
make
make run

Build artifacts:

• build/boot.bin
• build/kernel.bin
• build/inject_transport
• build/mini_os.img

Quick Usage in Shell

Typical flow after boot:

mkdir docs
cd /docs
touch note.txt
edit note.txt
cat note.txt
mv note.txt note2.txt
ls

cd /transport/build
ls
run hello.bin
run calc.bin

Filesystem Snapshot

Sector layout in current implementation:

• LBA 0: boot sector
• LBA 1..100: reserved kernel area
• LBA 101: superblock
• LBA 102: inode bitmap
• LBA 103..110: data bitmap
• LBA 111..366: inode table
• LBA 367+: data blocks

Documentation Index

• Project overview: docs/Project_Overview.md
• Architecture: docs/Architecture.md
• Code structure: docs/Code_Structure.md
• Build and run: docs/Build_and_Run.md
• Shell and usage: docs/Shell_and_Usage.md
• C90 development guide: docs/C90_Development_Guide.md
• Filesystem (current implementation): docs/Filesystem_Current.md
• Filesystem design draft: docs/DIY-FS.md
• Real hardware boot guide: docs/Real_Hardware_Guide.md
• Known limitations: docs/Limitations_and_Roadmap.md

Real Hardware Note

Caution

MINI-OS uses a very primitive file system implementation and has known flaws (such as aggressive, brute-force disk read/write operations). Therefore, long-term use may increase hardware wear and tear.

Apart from this, MINI-OS does not perform any destructive operations on the machine. Nevertheless, to prevent potential data loss or hardware damage, it is still recommended to run it on a non-critical machine.

This project currently targets BIOS/CSM-style boot flows.

For USB boot on physical machines, read docs/Real_Hardware_Guide.md carefully.

Writing images to raw devices can destroy existing data on that device.