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97 lines
4.1 KiB
Markdown
97 lines
4.1 KiB
Markdown
os-tutorial
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===========
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_⚠️ Hey! This is an old, abandoned project, with both technical and design issues [listed here](https://github.com/cfenollosa/os-tutorial/issues/269). Please have fun with this tutorial but do look for more modern and authoritative sources if you want to learn about OS design. ⚠️_
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How to create an OS from scratch!
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I have always wanted to learn how to make an OS from scratch. In college I was taught
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how to implement advanced features (pagination, semaphores, memory management, etc)
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but:
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- I never got to start from my own boot sector
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- College is hard so I don't remember most of it.
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- I'm fed up with people who think that reading an already existing kernel, even if small, is
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a good idea to learn operating systems.
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Inspired by [this document](http://www.cs.bham.ac.uk/~exr/lectures/opsys/10_11/lectures/os-dev.pdf)
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and the [OSDev wiki](http://wiki.osdev.org/), I'll try to make short step-by-step READMEs and
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code samples for anybody to follow. Honestly, this tutorial is basically the first document but
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split into smaller pieces and without the theory.
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Updated: more sources: [the little book about OS development](https://littleosbook.github.io),
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[JamesM's kernel development tutorials](https://web.archive.org/web/20160412174753/http://www.jamesmolloy.co.uk/tutorial_html/index.html)
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Features
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--------
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- This course is a code tutorial aimed at people who are comfortable with low level computing. For example,
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programmers who have curiosity on how an OS works but don't have the time or willpower to start reading the Linux kernel
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top to bottom.
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- There is little theory. Yes, this is a feature. Google is your theory lecturer. Once you pass college,
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excessive theory is worse than no theory because it makes things seem more difficult than they really are.
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- The lessons are tiny and may take 5-15 minutes to complete. Trust me and trust yourself. You can do it!
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How to use this tutorial
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------------------------
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1. Start with the first folder and go down in order. They build on previous code, so if
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you jump right to folder 05 and don't know why there is a `mov ah, 0x0e`, it's because you missed lecture 02.
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Really, just go in order. You can always skip stuff you already know.
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2. Open the README and read the first line, which details the concepts you should be familiar with
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before reading the code. Google concepts you are not familiar with. The second line states the goals for each lesson.
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Read them, because they explain why we do what we do. The "why" is as important as the "how".
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3. Read the rest of the README. It is **very concise**.
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4. (Optional) Try to write the code files by yourself after reading the README.
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5. Look at the code examples. They are extremely well commented.
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6. (Optional) Experiment with them and try to break things. The only way to make sure you understood something is
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trying to break it or replicate it with different commands.
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TL;DR: First read the README on each folder, then the code files. If you're brave, try to code them yourself.
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Strategy
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--------
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We will want to do many things with our OS:
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- Boot from scratch, without GRUB - DONE!
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- Enter 32-bit mode - DONE
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- Jump from Assembly to C - DONE!
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- Interrupt handling - DONE!
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- Screen output and keyboard input - DONE!
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- A tiny, basic `libc` which grows to suit our needs - DONE!
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- Memory management
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- Write a filesystem to store files
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- Create a very simple shell
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- User mode
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- Maybe we will write a simple text editor
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- Multiple processes and scheduling
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Probably we will go through them in that order, however it's soon to tell.
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If we feel brave enough:
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- A BASIC interpreter, like in the 70s!
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- A GUI
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- Networking
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Contributing
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------------
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This is a personal learning project, and even though it hasn't been updated for a long time, I still have hopes to get into it at some point.
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I'm thankful to all those who have pointed out bugs and submitted pull requests. I will need some time to review everything and I cannot guarantee that at this moment.
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Please feel free to fork this repo. If many of you are interested in continuing the project, let me know and I'll link the "main fork" from here.
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