A simple 16bit OS that asks your name and says hello.

os.asm

MAX_STR_LEN equ 100

org 0x7c00
bits 16

mov ax, 0
mov ds, ax
mov es, ax
mov ss, ax
mov sp, 0x7c00

call cls

mov si, about
call puts

mov si, welcome
call puts

call gets

mov si, hello
call puts

mov si, string_buffer
call puts

mov si, nextline
call puts

main_loop:
jmp main_loop

about db '--- OS MADE BY ALIREZA AHANI ---', 0x0d, 0x0a, 0
welcome db 'Welcome, what is your name? ', 0
hello db 'Hello ', 0
string_buffer times MAX_STR_LEN db 0
nextline db 0x0d, 0x0a, 0

puts:
    pusha

    .loop
        lodsb
        or al, al
        jz .done

        mov ah, 0x0e
        int 0x10

        jmp .loop

    .done:
        popa
        ret

gets:
    mov bx, 0
    pusha

    .loop:
        mov ah, 0x00
        int 0x16

        cmp al, 0x0d
        je .done

        cmp bx, MAX_STR_LEN
        je .done

        mov ah, 0x0e
        int 0x10

        mov byte [string_buffer+bx], al
        inc bx

        jmp .loop

    .done:
        mov byte [string_buffer+bx], 0x00
        mov si, nextline
        call puts
        popa
        ret

cls:
    pusha
    mov ah, 0x00
    mov al, 0x03
    int 0x10
    popa
    ret

times 510-($-$$) db 0
dw 0xaa55