I want to read a file that is saved in hard drive to read through assembly language -

the codes shown below structure read file has been saved in computer. how can make program read hard drive? codes shown below sample of codes using in program

code segment  main proc far  ;housekeeping section  assume cs:code,ds:data,ss:stacks  mov ax,data ;establish addressability  mov ds,ax   ;to data segment  ;main process section  xor ax,ax  xor bx,bx  xor cx,cx  xor dx,dx  ;open file  mov ah,3dh  mov al,0  mov dx,offset file  int 21h  ;read file  mov bx,ax  mov ah,3fh  mov cx,40  mov dx,offset buffer  int 21h  jc error  ;closing file  mov ah, 3eh  int 21h  error:  mov ax, 4c00h  int 21h  main endp  code ends  data segment  file    db "file.txt",0  <----------- should put here make   codes read file hard drive  buffer  db 42 dup(?)    ;data buffer      data ends  stacks segment para stack 'stack'  dw  32 dup(?)  stacks ends  end