x16 PRos

About the Project

x16-PRos is a minimalistic 16-bit operating system written in NASM for x86 architecture. It supports a text interface, loading programs from disk, and basic system functions such as displaying CPU information, time, and date.

System Lightweight

x16-PRos is a lightweight system. On disk, it takes up only 12.5 kilobytes.

Extensibility

Ability to add your own 16-bit programs.

Educational

Great project for learning the principles of operating systems.

Understandability

All programs have convenient hints that will definitely help you understand everything.

x16 PRos includes a small set of built-in programs. You can add your own program to the system image and then run it using the load command, specifying the disk sector number where you wrote the program as an argument.

Here's how you can add a program:

dd if=YourProgram.bin of=disk_img/x16pros.img bs=512 seek=DiskSector conv=notrunc

× Warning! Do not write the program to sectors 1 through 5. The system itself is located there.

× Pay attention to the build file It shows which sectors are occupied by programs.

When trying to load sectors 1 through 5 using load, you will encounter artifacts or system freezes.

Supported commands in x16 PRos terminal

Basic set of x16 PRos terminal commands:

help display list of commands
info brief system information
cls clear screen
shut shut down the system
reboot restart the system
date display date
time show time (UTC)
CPU CPU information
load load program from disk sector (0000x800h)
writer start writer program
brainf start brainf interpreter
barchart start barchart program
snake start Snake game
calc start calculator program

x16 PRos Software Package

Basic x16 PRos software package includes:

Notepad for writing and saving texts to disk sectors
Brainf IDE for working with Brainf language
Barchart program for creating simple diagrams
Snake classic Snake game
Calc help with simple mathematical calculations

To run x16 PRos, use emulators such as QEMU or Bochs. Example command for QEMU:

qemu-system-x86_64 -fda x16-PRos-disk-image.img

You can also try running x16-PRos on a real PC (preferably with BIOS, not UEFI)

If you still want to run x16-PRos on a UEFI PC, you will need to enable "CSM support" in your BIOS. It may be called slightly differently.

Developer Documentation

Quick guide to developing programs for x16 PRos.

OS Architecture

Boot

The OS boots at address 0000x500h (500h in hexadecimal)

Memory

User programs are loaded at address 0000x800h

Disk

25 sectors are used
Programs are distributed across predefined sectors (see build-linux.sh)

Program Development

Program Requirements

Format: The program must be 16-bit executable code written in NASM
Organization: Use the org 800h directive
Termination: The program should return control to the OS in one of the following ways:
int 0x19 - reboot (highly recommended)
jmp 500h - return to shell

Available System Calls

Video Service (int 0x10)

AH=0x00 - set video mode
AH=0x02 - set cursor position
AH=0x0E - output character

Keyboard Input (int 0x16)

AH=0x00 - read character with wait

Disk Operations (int 0x13)

AH=0x02 - read sector
AH=0x03 - write sector

And other BIOS interrupts.

Minimal Program Example

[BITS 16]
[ORG 800h]  ; For user programs

start:
    ; Clear screen
    mov ax, 0x03
    int 0x10
    
    ; Display message
    mov si, hello_msg
    call print_string
    
    ; Wait for key press
    mov ah, 0x00
    int 0x16
    
    ; Terminate program
    int 0x19

print_string:
    mov ah, 0x0E
    mov bh, 0x00
    mov bl, 0x0F
.print_char:
    lodsb
    cmp al, 0
    je .done
    int 0x10
    jmp .print_char
.done:
    ret

hello_msg db 'Hello, x16 PRos!', 0

Limitations

No multitasking support
No memory protection
Limited set of system calls
Maximum program size - several sectors (can be increased in build-linux)

x16-PRos Developers

PRoX (Faddey Kabanov) lead developer. Creator of the kernel, command interpreter, writer, brainf, snake programs.
Loxsete developer of the barchart program.
Saeta developer of the calculation logic in the program "Calculator".

Contribute to the Project

If you want to contribute to the development of x16 PRos, you can:

Report bugs via GitHub Issues.

Suggest improvements or new features on GitHub.

Help with documentation by emailing us at prox.dev.code@gmail.com.

Develop new programs for the system.

The project is distributed under the MIT license. You are free to use, modify and distribute the code.

MIT License:


Copyright © 2025 PRoX2011 (Faddey Kabanov)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files ("x16-PRos"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Note: We especially welcome contributions in the form of documentation, sample programs and tests.