ASM Calculator BIOS

🇬🇧 English | 🇷🇺 Русский

A simple calculator written in 16-bit x86 Assembly running directly on BIOS.

The project contains a custom bootloader and a small kernel that performs arithmetic operations without using any operating system.

Features

• Integer addition
• Integer subtraction
• Integer multiplication
• Integer division
• Signed 16-bit integer support
• Colored VGA text output
• Input validation
• Backspace support
• Overflow detection
• Division-by-zero handling
• Invalid operation handling
• Custom bootloader
• Modular kernel structure
• BIOS keyboard input
• BIOS text output
• 16-bit Real Mode
• NASM syntax

Requirements

• NASM
• QEMU
• x86 emulator or real hardware with BIOS support

Build

make

Manual build:

nasm -f bin src/boot/boot.asm -o bin/boot.bin
nasm -f bin src/kernel/main.asm -o bin/kernel.bin

Create disk image:

cat bin/boot.bin bin/kernel.bin > bin/disk.img

Run

Using QEMU:

qemu-system-i386 -drive format=raw,file=bin/disk.img

Example

How it works

The calculator starts from a custom bootloader and runs in 16-bit Real Mode.

No operating system is required.

The project uses BIOS interrupts:

• INT 10h (0x10) — video services for text output
• INT 16h (0x16) — keyboard input

The kernel implements:

• string input
• string-to-integer conversion
• integer-to-string conversion
• arithmetic operations
• result printing

Limitations

• Supports only signed 16-bit integers (-32768..32767)
• BIOS systems only
• Floating-point arithmetic is not supported

Project Structure

.
├── src/
│   ├── boot/
│   │   └── boot.asm
│   └── kernel/
│       ├── color.asm
│       ├── data.asm
│       ├── io.asm
│       ├── math.asm
│       └── main.asm
├── bin/
│   ├── boot.bin
│   ├── kernel.bin
│   └── disk.img
├── docs/
│   └── cat.gif
├── Makefile
├── LICENSE
├── README.md
└── README_RU.md

Development

The kernel is loaded by the custom bootloader at address 0x7E00.

The project is split into the following modules:

• boot.asm — bootloader
• main.asm — kernel entry point
• io.asm — keyboard input and text output
• math.asm — arithmetic and number conversion
• color.asm — VGA color management
• data.asm — strings, buffers and global variables

About

This project is a low-level x86 Assembly experiment focused on BIOS programming and operating system independent execution.

The goal was to practice:

• 16-bit x86 Assembly
• BIOS interrupts
• Real Mode programming
• Bootloader development
• Low-level input/output
• Memory layout and binary loading

Completed

• Calculator on libc (System V ABI) - 🔗 asm-calc-libc
• Calculator using raw syscalls (no libc) - 🔗 asm-calc-syscall
• 16-bit BIOS calculator with custom bootloader - 🔗 asm-calc-bios

License

MIT

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