NanoKernel

A tiny two-stage x86 operating system that boots from a 512-byte boot sector into a real interactive shell — with system-info tools and two built-in games. Written from scratch in NASM assembly.

Stack

• Language: x86 real-mode assembly (NASM)
• Firmware interface: BIOS interrupts — int 0x10 (video), int 0x16 (keyboard), int 0x13 (disk), int 0x15 (memory), int 0x1A (timer), CPUID
• I/O: direct VGA text buffer (0xB800) + a 16550 UART serial console (COM1)
• Tooling: NASM to assemble, QEMU to run

Description

NanoKernel started life as a single 512-byte boot-sector shell (still preserved in legacy/). It has since grown into a two-stage system: a small boot sector (boot/stage1.asm) loads a larger second-stage kernel (kernel/stage2.asm) from disk and jumps to it. Stage 2 is a proper little text-mode environment — its own console with scrolling and colour, a command shell, BIOS-backed system-info commands, and two games — all in real mode, no OS underneath.

Every character printed is also mirrored to the serial port, so NanoKernel can be driven and scripted over COM1 as well as from the keyboard.

Features

• Two-stage bootloader — a valid 512-byte boot sector that loads the kernel sector-by-sector (handling track/head boundaries) and hands off control.
• Text-mode console — direct 0xB800 writes with a hardware cursor, line scrolling, backspace, and selectable colour.
• Command shell with:
  • help — list commands
  • echo <text> — print text
  • clear / cls — clear the screen
  • color <0-15> — set the text colour
  • sysinfo — CPU vendor via CPUID, RAM size via BIOS int 15h/E801, boot drive
  • mem — full BIOS E820 memory map (base / length / type)
  • about — banner and credits
  • reboot — restart via the 8042 controller
  • shutdown — ACPI power-off (QEMU)
• Games:
  • guess — number-guessing game (1–100) with higher/lower feedback
  • snake — a real-time text-mode snake with score, growing tail, and food

How to Build / Run

You need nasm and qemu.

# build the bootable floppy image -> build/nanokernel.img
./build.sh           # or: make

# run it in QEMU
make run             # or: qemu-system-i386 -drive file=build/nanokernel.img,format=raw,if=floppy

Drive it over serial

NanoKernel's shell reads from COM1 as well as the keyboard, so you can script it:

qemu-system-i386 -drive file=build/nanokernel.img,format=raw,if=floppy \
                 -display none -serial tcp:127.0.0.1:4455,server,nowait
# then connect to 127.0.0.1:4455 and type commands

Project layout

Path	What it is
boot/stage1.asm	512-byte boot sector; loads and jumps to stage 2
kernel/stage2.asm	the mini-kernel: console, shell, sysinfo, games
build.sh / Makefile	assemble the two stages into a bootable image
legacy/boot_shell.asm	the original single-sector shell NanoKernel grew from

License

Released under the MIT License.