assume cs:codesg,ds:datasg
datasg segment
db 'ibm             '
db 'dec             '
db 'dos             '
db 'vax             '
datasg ends

codesg segment
start: mov ax,datasg
       mov ds,ax
       mov bx,0

       mov cx,4
   s0: mov si,0
       mov cx,3
    s: mov al,[bx+si]
       and al,11011111b
       mov [bx+si],al

       inc si

       loop s

       add bx,16
       loop s0

       mov ax,4c00h
       int 21h
codesg ends
end start