http://sebastianmihai.com/snowdrop/

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[ideo_snowd] Snowdrop OS - a homebrew operating system from scratch,
in assembly language

  * Introduction
  * Binaries and Sources
  * Visuals
  * Organization
  * Apps
  * System Calls
  * Game Development
  * GUI Framework
  * BASIC
  * x86 Assembler
  * x86 Debugger
  * Development Log

Introduction section


Welcome to the pages of Snowdrop OS, my homebrew operating system
project.

[snowdrop-i]

Snowdrop OS was born of my childhood curiosity around what happens
when a PC is turned on, the mysteries of bootable disks, and the
hidden aspects of operating systems. It is a 16-bit real mode
operating system for the IBM PC architecture. I designed and
developed this homebrew OS from scratch, using only x86 assembly
language.

I have created and included a number of utilities, including a file
manager, text editor, graphical applications, BASIC interpreter, x86
assembler and debugger. I also ported one of my DOS games to it.
After all, what kind of an operating system doesn't have games?

The Snowdrop OS and the apps are distributed as both a floppy disk
(1.44Mb) image, as well as a CD-ROM image. The images contain the
following, all programmed from scratch:

  * a boot loader which loads the kernel into memory
  * a kernel which sets up interrupt vectors to be used by user apps,
    and then loads the startup app
  * user apps, including a shell (command line interface), utilities,
    test apps, and aSMtris, my Tetris clone

Snowdrop OS can also be installed to a hard disk - prompting the user
to do so during boot - if it detects one.

I hope that Snowdrop can serve other programmers who are looking to
get a basic understanding of operating system functions. Like my
other projects, the source code is fully available, without any
restrictions on its usage and modification.



Source code browser


Some interesting areas in the source code are:

  * Boot loader is crammed into 512 bytes; it locates and loads the
    kernel
  * Snowdrop OS's kernel provides fundamental services and
    abstractions to applications
  * Graphics and GUI framework are the foundations needed to create
    graphical, mouse-driven applications
  * Snowdrop's x86 assembler can be used to create low-level
    applications directly inside Snowdrop OS
  * BASIC interpreter is great for creating high-level applications
    quickly
  * The x86 debugger can be used in conjunction with the assembler
  * Dynamic data structure libraries for working with linked lists,
    trees, BSTs, etc.
  * All applications games, text editor, file manager, tools, test
    applications



Versions


v1 - initial version, single tasking, shell, aSMtris
v2 - PS/2 mouse driver and mouse test apps
v3 - basic multi-tasking support and virtual display support
v4 - FAT12 driver write/delete, file manager, text editor
v5 - serial port driver, formatting utilities, file copy support
v6 - multiplayer snake game (over serial port)
v7 - slide show presentation app
v8 - "keep memory" task lifetime mode, for custom services
v9 - parallel port driver, BMP image support, sprites
v10 - system timer frequency change
v11 - animated sprites, sound driver (internal speaker)
v12 - keyboard driver
v13 - more sprites functionality, Storks game
v14 - kernel config, program arguments, file utilities
v15 - 16x2 LCD controller app, text editor fixes
v16 - GUI framework
v17 - Snowmine (Minesweeper-like game)
v18 - BASIC interpreter and linker
v19 - install to hard disk
v20 - BASIC and text editor improvements
v21 - integration of BASIC and GUI framework
v22 - x86 assembler, multi-disk support, file view utilities
v23 - x86 debugger
v24 - service loading
v25 - dynamic memory and data structures
v26 - installer improvements, pseudo-mouse driver
v27 - kernel and inter-task messaging
v28 - GUI higher resolution, draw application, desktop application
v29 - data compression, Hangman game
v30 - pseudo-mouse driver improvements
v31 - runtime libraries (RTL), BASIC interpreter RTL

[snowdrop_m]