followed is the code:
.model small
.stack 256
tes  db  'M'
mov  ax,@data
mov  ds,ax
mov    ah,00
mov    al,07h
int    10h

mov  ah,09h
mov  al,'M'
mov  bh,0h
mov  bl,01h
mov  cx,2h
int    10h
mov    ah,4ch
int    21h
end      start
;the runing environment is a DOS6.22 virtual machine.
Posted on 2005-05-09 09:11:13 by photon
Emulation of EGA in virtual machine covers only main functionality, underscoring seems not no be among them. If you run your program in real DOS, it will work as expected.
It also runs in my WinXP NTVDM fullscreen:

  • set the console window property to 80*25

  • enlarge to fullscreen (Alt-Enter)

  • run your program

Double underlined MM will be displayed then.
Posted on 2005-05-09 14:11:09 by vit$oft
I have tried again according your second methord, program run smothly adn successfuly!
I beg you give me a hint about the reason!
Posted on 2005-05-10 07:47:58 by photon