littleosbook - OS Development Book

littleosbook provides a comprehensive guide for developers on creating an x86 operating system from scratch, emphasizing low-level programming and system design. The main topics are setting up a development environment with tools like GCC and NASM, and using emulators like Bochs. It also involves creating a GRUB-compatible bootloader to switch from BIOS to kernel execution. The guide outlines important concepts like memory segmentation and the Global Descriptor Table (GDT), explaining how logical addresses correspond to physical addresses. It explains interrupts, focusing on managing hardware events with the Interrupt Descriptor Table (IDT) and configuring the Programmable Interrupt Controller (PIC) to handle signals from devices such as keyboards. The guide emphasizes transitioning to user mode, which involves loading and executing external programs in memory. This necessitates the implementation of GRUB modules and an appropriate configuration of privilege levels. The page explains virtual memory through paging, emphasizing the significance of identity paging and address translation for effectively mapping virtual memory to physical resources. For kernel memory management, the guide discusses higher-half kernel paging to avoid conflicts with user applications. Developers focus on essential system programming skills, such as serial communication, buffer configuration, modem control, and writing data to the serial port. These features are critical for debugging and managing hardware interactions. The page discusses key concepts like kernel development, creating user-mode processes, multitasking with preemptive scheduling using the Programmable Interval Timer (PIT), and efficient memory management through page frame allocation.

The guide is freely available and open-source, making it an accessible resource for anyone interested in operating system development.