Simple Operating System

A 32-bit x86 operating system built from scratch in C and NASM assembly — bootloader to GUI to TCP/IP stack.

Blog & Demo

• 自幹作業系統 - Simple OS
• 自幹作業系統 - Networking Fundamentals
• 自幹作業系統 - 初探 Timer 原理
• 自幹作業系統 - Task and Scheduler
• 自幹作業系統 - Context Switch
• Demo / 錄影

What's Implemented

Area	Details
Boot	GRUB → boot.S → main.c, GDT/IDT, IRQ handling
Memory	Physical memory manager, kernel heap, MMU paging
Multitasking	PIT timer, context switch, round-robin scheduler
Processes	fork / exec / wait / exit, Ring 0↔3 transition, IPC, Mutex
File System	ATA driver, MBR parser, SimpleFS, VFS, ELF loader
Shell & CLI	shell, ls, cat, touch, mkdir, rm, ps, top, kill, ping
GUI	VESA framebuffer, window manager, double buffering, PS/2 mouse/keyboard
Window Apps	clock, notepad, paint, image viewer, file explorer, task manager, tic-tac-toe
Networking	RTL8139 driver, Ethernet, ARP, IPv4, ICMP, UDP, TCP, DNS, HTTP, wget
User libc	malloc / free / printf, syscall wrappers, crt0.S

The final kernel binary (myos.bin) is ~62 KB.

Quick Start

Requires Docker (macOS: OrbStack) and QEMU.

make build-env   # Build the Docker cross-compile image (one-time)
make all         # Compile kernel + user apps → myos.iso
make run         # Boot in QEMU
make debug       # Boot with interrupt logging (-d int -no-reboot)
make clean       # Remove build artifacts

Architecture

Boot sequence: GRUB → src/kernel/arch/x86/boot.S → src/kernel/init/main.c

src/
├── kernel/
│   ├── arch/x86/    # Boot, GDT/IDT, paging, PIT, context switch
│   ├── mm/          # Physical memory (pmm.c), kernel heap (kheap.c)
│   ├── kernel/      # Scheduler, task lifecycle, syscall dispatch, GUI/WM
│   ├── fs/          # VFS, SimpleFS, ELF loader, ATA, MBR
│   ├── drivers/     # VESA, TTY, PS/2 keyboard/mouse, RTC, PCI, RTL8139
│   ├── net/         # Ethernet → ARP → IPv4 → ICMP/UDP/TCP
│   ├── lib/         # Kernel printf, string/memory utilities
│   └── include/     # All kernel headers
└── user/
    ├── bin/         # ~29 standalone ELF applications
    ├── lib/         # Minimal libc
    └── asm/         # crt0.S (user-space C runtime entry)

• Kernel linked at physical base 0x100000 via scripts/linker.ld
• Syscalls via int 0x80, dispatched in src/kernel/kernel/syscall.c
• User processes run in Ring 3; each .c in src/user/bin/ becomes a standalone ELF

Prerequisites

• Basic C and x86 assembly
• Familiarity with computer organization concepts
• macOS or Ubuntu 24.04
• Docker (OrbStack recommended on macOS) + QEMU