PrimusOS

A minimal 32-bit x86 operating system written in C and Assembly, featuring a custom shell, FAT32 filesystem, ATA disk driver, and basic runtime (heap, math, crypto).

Built from scratch for learning low-level systems programming.

---

Features

• FAT32 filesystem driver with ATA PIO disk I/O (read/write)
• Persistent shell history stored on disk (FAT32-backed)
• Interactive shell with command history navigation (↑)
• Multiboot-compliant kernel (GRUB / QEMU -kernel)
• VGA text mode terminal with color support
• PS/2 keyboard driver (capslock, shift, arrow keys)
• Heap memory allocator
• Mathematical functions (sin, cos, tan, sqrt, pow, log, etc.)
• SHA-224 and SHA-256 cryptographic hashing
• RPN calculator
• Easter eggs

---

Dependencies

Arch Linux

sudo pacman -S gcc nasm qemu-system-x86 mtools xorriso

Ubuntu / Debian

sudo apt update
sudo apt install build-essential nasm qemu-system-x86 mtools xorriso

Fedora

sudo dnf install gcc nasm qemu-system-x86 mtools xorriso make

---

Building

make primus-os.bin

---

Running

# Create disk image (first time only)
make create-disk

# Run in QEMU
make run-qemu

---

Generating a bootable ISO

make primus-os.iso

---

Shell commands

Command	Description
help	List all commands
about	About PrimusOS
math	List mathematical functions
crypto	List cryptography utilities
history	Show command history
clear	Clear the screen
datetime	Show current date and time
date	Show current date
clock	Show current time
fontcolor	Change terminal font color
reboot	Reboot the system
shutdown	Shutdown the system
sha256(x)	SHA-256 hash of x
sha224(x)	SHA-224 hash of x
sin(x), cos(x), ...	Math functions

---

Architecture

High-level overview of kernel subsystems:

src/
├── loader.s        # Multiboot entry point
├── kernel.c        # Shell loop, command dispatcher
├── tty.c           # VGA terminal
├── io.c            # Port I/O, keyboard
├── ata.c           # ATA PIO disk driver
├── fat32.c         # FAT32 filesystem (read/write)
├── memory.c        # Heap allocator
├── string.c        # String utilities
├── math.c          # Math functions
├── sha224.c        # SHA-224
├── sha256.c        # SHA-256
├── calculator.c    # RPN calculator
└── shell_history.c # Persistent command history

---

Roadmap

Near term

• Filesystem commands (ls, cat, write)
• Full FAT32 write support (cluster allocation)

Medium term

• Basic text editor
• Multithreading

Long term

• VGA graphics modes
• Games (tic-tac-toe, chess)

---

Contributing

Please open an issue before submitting a pull request.

---

License

GNU General Public License v3.0