os-study's Introduction

My simple educational OS for learning purpose. It is bootable in Bochs Emulator, by a virtual flobby disk created by the Makefile, disk.dsk. A big thanks to Broken Thorn’s OS Development series. I must say, this is the best free document for learning how to actually write an OS, not just learning about the concepts, or being confined in some assignment framework where many things are already done and you fill in function body. Although the core material is good overall, some important content is missing and you have to figure it out on your own, otherwise you will get stuck forever. When it comes to code, you are also on your own. The code example is fine, but many are outdated (because newer nasm) or missing important parts. You have to fix it yourself, if you want to proceed through the series. But, this is a good thing to me; I consider this a chance for exercising. I believed you truly understand something when you actually work on it, not just being spoon fed. I learned so much from this.

Current state

The OS does not have a file system, because I want to leave it later. So, different parts of the OS is hard coded in the virtual flobby disk by sectors. For example, the kernel is allocated with 15 sectors, interrupt handling code is allocated with 12 sectors and so on. You can check in the target boot.dsk in the Makefile.

Bootloader (first 512 bytes in Master Boot Record)
Second stage bootloader
Basic VGA text output.
Kernel space code (ring 0) It includes code + data descriptor in Global Descriptor Table.
Interrupts handling code: currently handles CPU exceptions (i.e. dividie by 0), PIC interrupts.
Userspace code (ring 3): code + data descriptor in Global Descriptor Table.
Getting memory informaton: total number of memory and system memory map.
Virtual memory managment (in progress).

Demo: