SUB-OS is a modular monolithic 64-bit x86_64 operating system designed and engineered from scratch following modern Linux kernel architectural patterns and incorporating the LazyBox multi-call userland binary suite.

🌟 Key Features

64-Bit Long Mode Bare-Metal Core: Custom two-stage MBR bootloader with BIOS E820 memory mapping and 4GB 4-level PML4 identity paging.
Modular Monolithic Linux Layout: Clean directory structure (arch/, kernel/, mm/, drivers/, fs/, net/, crypto/, lib/, userland/).
Preemptive Multitasking Scheduler: Round-Robin scheduling driven by 8254 PIT (100 Hz, 10ms resolution) with atomic spinlocks & semaphores.
Physical & Dynamic Memory Management: 64-bit Page Frame Allocator (4 KB bitmap) and Kernel Dynamic Heap (4 MB pool) with boundary tag splitting and coalescing.
Virtual File System (VFS): Path resolver (vfs_namei), file descriptors (64 max), in-memory RAMFS, synthetic /dev device filesystem, and /proc dynamic system metrics filesystem.
Hardware Drivers:
- Char: VGA Text Mode, Virtual Terminals TTY1-4 with ANSI escape parsing, 16550 UART Serial (COM1), PS/2 Keyboard with circular buffer.
- Block: ATA / IDE Hard Disk PIO driver (28-bit LBA).
- PCI: PCI Bus Enumeration & MMIO BAR configuration.
- Network: Intel 82540EM/82545EM Gigabit Ethernet NIC with circular DMA RX/TX rings.
- Sound: PC Speaker square-wave tone generator.
Network Protocol Stack: Ethernet encapsulation, ARP resolution table, IPv4 routing/checksums, and ICMP Echo client/server (ping).
Kernel Cryptographic Engine: FIPS 180-4 SHA-256, RFC 1321 MD5, IEEE 802.3 CRC32, and Xorshift128+ CSPRNG.
LazyBox Multi-Call Userland Suite: 42 built-in applets with history, arrow-key line editing, and ANSI color support.

📁 Source Tree

├── arch/x86_64/            # Hardware-specific CPU, paging, and entry code
│   ├── boot/               # 64-bit kernel entry point (entry.asm)
│   ├── cpu/                # GDT/TSS, IDT (256 gates), Dual 8259A PIC, 8254 PIT, CPUID
│   └── mm/                 # 4-Level PML4 Paging & TLB management
├── boot/                   # Custom two-stage MBR bootloader
│   ├── boot.asm            # Stage 1: 512-byte MBR loader (INT 13h LBA/CHS)
│   └── stage2.asm          # Stage 2: A20, E820 Memory Map, 4GB Identity Paging, Long Mode switch
├── kernel/                 # Core Monolithic Kernel Engine
│   ├── main.c              # 11-step master initialization sequence
│   ├── printk.c            # ANSI loglevel printk with 64KB dmesg ringbuffer & COM1 serial port output
│   ├── panic.c             # Kernel panic screen with 64-bit register dump
│   ├── task.c              # Task Control Blocks (PCB) & Process Management
│   ├── sched.c             # Preemptive Round-Robin Multi-Tasking Scheduler
│   └── sync.c              # Atomic spinlocks and semaphores
├── mm/                     # Memory Management Subsystem
│   ├── pmm.c               # 64-bit Physical Page Frame Allocator (4 KB bitmap)
│   └── kmalloc.c           # Kernel Dynamic Heap Allocator (4 MB initial pool)
├── drivers/                # Device Driver Tree
│   ├── char/               # VGA text driver, Virtual Terminals TTY1-4, 16550 UART COM1, PS/2 Keyboard
│   ├── block/              # ATA / IDE Hard Disk PIO driver (28-bit LBA)
│   ├── pci/                # PCI Bus Enumerator & BAR mapping
│   ├── net/                # Intel 82540EM/82545EM Gigabit Ethernet NIC Driver (Circular DMA Rings)
│   └── sound/              # PC Speaker tone generator & PIT Channel 2
├── fs/                     # Virtual File System (VFS)
│   ├── vfs.c               # VFS core, path resolver (vfs_namei), file descriptor table (64 max)
│   ├── ramfs.c             # In-memory RAM filesystem
│   ├── devfs.c             # Synthetic Device Filesystem (/dev/null, /dev/zero, /dev/random, /dev/tty)
│   └── procfs.c            # Dynamic Information Filesystem (/proc/version, /proc/meminfo, /proc/cpuinfo)
├── crypto/                 # Kernel Cryptographic Engine
│   ├── sha256.c            # FIPS 180-4 Standard SHA-256 Digest
│   ├── md5.c               # RFC 1321 MD5 Message-Digest
│   ├── crc32.c             # IEEE 802.3 32-bit Cyclic Redundancy Check
│   └── prng.c              # Xorshift128+ High-Performance CSPRNG
├── net/core/               # Network Protocol Stack
│   └── net.c               # Ethernet encapsulation, ARP Table, IPv4 routing, ICMP Echo ping client/server
├── lib/                    # Standard Kernel Runtime Library
│   ├── string.c            # String & memory manipulation
│   ├── vsprintf.c          # vsnprintf with width, alignment, and formatting
│   └── bitmap.c            # Bit manipulation utilities
└── userland/lazybox/       # Userland Shell & Multi-Call Suite
    ├── lazybox.c           # Multi-call binary dispatcher with 42 applets
    └── shell.c             # Interactive terminal shell (history, tab-completion, ANSI color)

⚡ 11-Step Master Boot Pipeline

[1/11] GDT & TSS: 64-bit flat segment selectors + Task State Segment with dedicated 64KB kernel stack.
[2/11] IDT & ISRs: 256-entry Interrupt Gate Table with CPU exception and hardware IRQ handlers.
[3/11] Dual 8259A PIC: Remapped hardware IRQs 0-15 to vectors 32-47 with cascade handling.
[4/11] 8254 PIT Timer: Configured for 100 Hz (10ms resolution) driving preemptive multitasking.
[5/11] PS/2 Keyboard: Full scancode translation table with Shift, CapsLock, and circular buffer.
[6/11] Physical Memory Manager: 64-bit frame allocator tracking 128 MB RAM (31,712 free pages).
[7/11] Kernel Dynamic Heap: 4 MB initial pool with boundary tag headers, coalescing, and reallocation.
[8/11] ATA / IDE Hard Disk: 28-bit LBA PIO controller supporting read/write operations.
[9/11] PCI & Intel E1000 NIC: Intel Gigabit Ethernet controller (52:54:00:12:34:56), DMA RX/TX rings.
[10/11] Virtual File System: Root RAMFS, /dev synthetic device filesystem, /proc dynamic info filesystem.
[11/11] LazyBox & Scheduler: Preemptive scheduler initialization and interactive multi-call binary userland.

🛠️ Build and Run

Prerequisites

nasm (>= 2.15)
x86_64-elf-gcc (>= 13.0) & x86_64-elf-ld
qemu-system-x86_64
make

Commands

# Build the 1.5MB bootable disk image
make

# Launch in QEMU with Intel E1000 Gigabit NIC
make run

# Clean build artifacts
make clean

💻 LazyBox Applet Reference

  [Filesystem]
    ls           cat          touch        mkdir        wc
  [Crypto]
    md5sum       sha256sum    crc32
  [Network]
    ifconfig     ping         arp
  [Storage]
    hdparm
  [System]
    uname        free         uptime       dmesg        sleep
  [Terminal]
    clear
  [Core]
    lazybox      echo         neofetch

📄 License

This project is open-source software licensed under the MIT License.