I want to build a small operating system as an educational project—to understand how complex software works, practice systems programming, create something useful for my portfolio, and explore related areas of computer science. My goal is a basic university-level OS that demonstrates concepts such as memory allocation, process scheduling, system calls, and perhaps simple device drivers.
I assume I should begin with computer architecture and assembly language, but I'm unsure how much of an operating system is actually written in assembly. I also don't understand where compilers, libraries, debuggers, and drivers fit into the learning path, or how to compile and debug a system that cannot simply rely on a normal desktop toolchain.
What sequence of topics would you recommend? Are there textbooks or courses that can be followed in order—for example, computer architecture, then assembly and C, followed by operating-system implementation? I'd especially appreciate resources that guide the reader through building a small OS rather than only explaining theory.
4 Answers
Do not overlook the toolchain. An OS normally cannot use the host system’s libraries or assumptions, so you will eventually learn about freestanding C, cross-compilation, object files, linking, linker scripts, binary formats, and debugging with an emulator. Standard libraries are not automatically available inside the kernel; you either provide small replacements or initially avoid them. Drivers are part of operating systems, but begin with simple console and timer devices before tackling storage, networking, or graphics.
Start by defining the scope. A tiny educational kernel is very different from a full desktop operating system. For a manageable project, target one architecture and run it in an emulator. Implement a boot path, basic kernel entry, text or serial output, interrupts, memory management, a simple scheduler, system calls, and perhaps a minimal filesystem. You do not need to build every driver or support multiple processors and users at first.
Learn C, basic data structures, computer organization, assembly, and then operating-system concepts. Most of the kernel can be written in C, with a small amount of assembly for bootstrapping, interrupt entry, context switching, and other architecture-specific work. You will also need a cross-compiler, linker scripts, an emulator, and a debugger, but these can be introduced as you reach each stage.
A practical project roadmap would be: boot a kernel, print diagnostic output, set up a descriptor or exception table, handle interrupts, add physical and virtual memory management, implement threads and context switching, add a scheduler, expose a few system calls, and finally run simple user programs. Keep the design deliberately small and document every stage. This gives you a complete learning project without requiring you to recreate all the features of a production operating system.
A useful learning sequence is: become comfortable with C and pointers; study digital logic and computer architecture; learn enough assembly to read calling conventions, registers, stack frames, and interrupt code; then study OS fundamentals while implementing each topic. You do not need to master all of assembly before starting, but you should understand the target CPU’s architecture and how compiled C interacts with it.
For resources, combine a systems programming or C text with a computer-organization book, then use an operating-systems text that includes projects. The xv6 source and accompanying commentary are particularly useful for seeing a small Unix-like kernel, while an OS course with staged labs can provide structure. Build and test one feature at a time in an emulator instead of attempting the whole system at once.
That scope sounds much closer to what I mean: implementing a basic version of the concepts usually covered in an introductory operating-systems course, rather than trying to create a general-purpose desktop OS.