How to Make Your Own Operating System

Introduction

Step 1—understand what you are about to build and why. Building an OS from scratch is less about producing a Linux replacement the first time and more about learning how computers work: boot process, CPU modes, memory layout, interrupts, drivers, and scheduling. Expect a steep learning curve, but also rewarding clarity about low-level computing.

Step 2—accept constraints. Start with a tiny, well-defined goal: a bootable image that prints text on screen, accepts keyboard input, and can run tiny programs. Expand from there.

Step 3—keep safety in mind. Use emulators (QEMU/VirtualBox) for development and debugging. Don’t flash untested code to real hardware until you understand the consequences.

Decide your target and scope.

Step 1—pick BIOS+GRUB (legacy) or UEFI. BIOS+GRUB with a Multiboot header is the simplest path for a first hobby OS; GRUB handles many low-level tasks for you. UEFI is modern and necessary if you want a pure 64-bit path early but adds complexity.

Step 2—pick 32-bit or 64-bit. Many tutorials start with a 32-bit protected-mode kernel (easier entry), then move to 64-bit (long-term). If you already know x86_64 assembly, you may opt for a 64-bit kernel via UEFI or Multiboot2.

Step 3—define minimal initial features: boot → kernel entry → print text → wait forever. Later add keyboard, timers, interrupts, memory management, a simple scheduler, a file system, and user programs.

Prerequisites

Step 1—know C and a little assembly. C is the primary language for kernels; assembly is used for the entry code and low-level constructs.

Step 2—Know basic computer architecture concepts: CPU registers, stack, memory addressing, interrupts, and I/O ports.

Step 3—be comfortable with the command line: make, gcc/ld/objcopy, and basic file operations.

Step 4—Choose your development host: Linux (recommended) or macOS/WLS. Windows users should use WSL2 or a Linux VM.

Tools and environment setup

Step 1—install an emulator for testing:QEMU is the most convenient (qemu-system-i386 or qemu-system-x86_64).

Step 2—install an assembler and linker: NASM or GAS, and LD. For 32-bit builds on a 64-bit host, install gcc-multilib or a cross-compiler.

Step 3—install GRUB tools: grub-mkrescue (often packaged with GRUB) and an ISO tool like xorriso if required.

Step 4—consider a cross-compiler. A cross-compiler (e.g., i686-elf-gcc) avoids toolchain mismatch. For quick experiments, gcc -m32 is often enough on Linux with multilib installed.

Step 5—get a text editor or IDE you like; version control (git) is helpful.

Project layout and files

Step 1—Create a small, tidy project tree:

• boot.s—assembly holding multiboot header/entry glue
• kernel.c—kernel main and basic functions
• linker.ld—linker script to place sections
• grub.cfg—GRUB menu entry
• Makefile—automate build steps
• isodir/—temporary folder to assemble ISO contents

Step 2—Keep a single directory initially so paths are simple. As the project grows, split it into src/, lib/, drivers/, and user/.

Step: Create a bootable image that GRUB can load.

Step 1—write a minimal grub.cfg.

Step 2—put the compiled ELF kernel into isodir/boot/ and copy grub.cfg into isodir/boot/grub/.

Step 3—Create the ISO with grub-mkrescue -o os-image.iso isodir.

Step 4—boot the ISO with QEMU:

qemu-system-i386 -cdrom os-image.iso

Step: Write the multiboot header and minimal entry code.

Step 1—create a very small assembly file boot.s with a Multiboot header so GRUB knows how to load your kernel.

Step 2—Include the magic number 0x1BADB002, flags, and checksum.

Step 3—add a minimal entry label so GRUB can jump into the kernel.

Step: Write a minimal kernel in C that prints to VGA.

Step 1—create kernel.c with a kernel_main() function.

Step 2—write to the VGA text buffer at 0xB8000.

Step 3—compile with -ffreestanding and -m32.

Step: Link the objects with a custom linker script.

Step 1—create linker.ld.

Step 2—link objects with ld -m elf_i386 -T linker.ld.

Step 3—place kernel.elf in ISO and boot with QEMU.

Step: Debugging the early boot

Step 1—Check GRUB messages.

Step 2—use objdump or readelf to inspect ELF headers.

Step 3—debug with QEMU and GDB.

Step: Add keyboard input and interrupts

Step 1—remap the PIC.

Step 2—set up an IDT.

Step 3—handle IRQ1 (keyboard).

Step 4—enable interrupts with STI.

Step: Add a timer and basic scheduling.

Step 1—program the PIT to generate IRQ0.

Step 2—implement a tick counter.

Step 3—design a simple scheduler.

Step 4—Test context switching with two tasks.

Step: Implement GDT and protected/long mode

Step 1—set up a GDT.

Step 2—load it with lgdt.

Step 3—If 64-bit, enable long mode and jump into it.

Step: Basic memory management and paging

Step 1—Use Multiboot to read the memory map.

Step 2—create a frame allocator.

Step 3—Implement page tables and enable paging.

Step 4—add a kernel heap allocator.

Step: Filesystem and initial ramdisk

Step 1—Include an initramfs via GRUB.

Step 2—read files from RAM.

Step 3—Later implement disk drivers and FAT.

Step: Loading and running user programs

Step 1—design a simple executable format.

Step 2—set up per-process address spaces.

Step 3—implement syscalls.

Step 4—run user programs in ring 3.

Step: Add basic drivers

Step 1—disk drivers.

Step 2—VGA or framebuffer console.

Step 3—network driver for virtual NIC.

Step: Build a userland and shell

Step 1—create small programs.

Step 2—build a shell to launch them.

Step 3—implement pipes and messaging.

Step: Improve tooling and automation

Step 1—write a Makefile.

Step 2—script frequent commands.

Step 3—Set up CI with QEMU.

Step: Use serial for debugging.

Step 1—add a COM1 serial driver.

Step 2—redirect output to host.

Step 3—automate tests over serial.

Step: Working with UEFI and 64-bit

Step 1—write UEFI boot apps.

Step 2—move to long mode.

Step 3—handle Secure Boot if needed.

Step: Version control and documentation

Step 1—use git.

Step 2—document ABI and syscalls.

Step 3—join OSDev communities.

Common pitfalls

Step 1—missing multiboot header.

Step 2—VGA writes crashing.

Step 3—bad IDT or privilege transition.

Step 4—mismatched compilation targets.

Next-level features

Step 1—advanced scheduler.

Step 2—journaling filesystems.

Step 3—networking stack.

Step 4—security features.

Testing and CI

Step 1—automate boot tests.

Step 2—capture output.

Step 3—run tests in CI.

Where to learn more

Step 1—CPU manuals.

Step 2—OS textbooks.

Step 3—study xv6 and Minix.

Step 4—OSDev Wiki.

Safety and tips

Step 1—always use emulators.

Step 2—backup work.

Step 3—stay patient.

Example workflow checklist

Step 1—write boot.s.
Step 2—write kernel.c.
Step 3—write linker.ld.
Step 4—compile and assemble.
Step 5—link into kernel.elf.
Step 6—prepare ISO with grub.cfg.
Step 7—run in QEMU.
Step 8—add features incrementally.

Conclusion

Building your own operating system is not just a programming project; it is a journey into how computers really work. The first time your “Hello, Kernel!” message appears on the screen, you realize that you have full control over the hardware beneath you. From there, every new feature—interrupts, memory management, processes, filesystems—teaches you concepts that will shape your understanding of software forever.

The key is patience and small, steady progress. No one writes a full Linux clone in one go, but by mastering each layer step by step, you create something that is uniquely yours. More importantly, you gain the confidence to understand and tinker with systems at their very core. Whether your OS becomes a playground, a learning tool, or the foundation for future projects, the knowledge you build will stay with you for life.

References

1. OSDev Wiki – Main Resource for OS Development
   👉 https://wiki.osdev.org/
2. Bran’s Kernel Development Tutorial (Legacy but Classic Guide)
   👉 http://www.osdever.net/bkerndev/Docs/title.htm
3. JamesM’s Kernel Development Tutorials
   👉 https://wiki.osdev.org/James_Molloy%27s_Tutorials
4. Intel® 64 and IA-32 Architectures Software Developer Manuals
   👉 https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
5. Operating Systems: Three Easy Pieces (OSTEP) — Free Online Book
   👉 https://pages.cs.wisc.edu/~remzi/OSTEP/
6. Minix 3 Official Website (Educational OS Project by Andrew Tanenbaum)
   👉 https://www.minix3.org/
7. xv6: A Simple Unix-like Teaching Operating System
   👉 https://pdos.csail.mit.edu/6.828/2020/xv6.html
8. GNU GRUB Manual (Bootloader Reference)
   👉 https://www.gnu.org/software/grub/manual/
9. QEMU Official Documentation (Emulator for OS Testing)
   👉 https://www.qemu.org/docs/master/
10. Linux From Scratch Project (Learn by Building Your Own Linux Distro)
    👉 https://www.linuxfromscratch.org/