检测点13.1
     comment            ;
1、转移地址在bx中，所以最大偏移位移是ffff
2、编写新的7ch中断 
;       
              assume    cs:code
        data  segment
              db        'conversation',0
        data  ends
        code  segment
      start:
              push      cs
              pop       ds
              mov       si,offset begin
              mov       ax,0
              mov       es,ax
              mov       di,200h
              mov       cx,offset over-offset begin
              cld
              rep       movsb
;修改中断向量表      
              mov       ax,0
              mov       ds,ax
              mov       word ptr ds:[7ch*4],200h
              mov       word ptr ds:[7ch*4+2],0
;测试程序      
              mov       ax,data
              mov       ds,ax
              mov       si,0
              mov       ax,0b800h
              mov       es,ax
              mov       di,12*160
          s:
              cmp       byte ptr [si],0
              je        ok
              mov       al,[si]
              mov       es:[di],al
              inc       si
              add       di,2
              mov       bx,offset s-offset ok
              int       7ch
         ok:
;暂停
              mov       ah,1
              int       21h
;退出         
              mov       ax,4c00h 7
              int       21h
      begin:
              push      bp
              mov       bp,sp
              add       [bp+2],bl
              pop       bp
              iret
       over:  nop
        code  ends
              end       start
检测点13.2
(1)不对，因为ffff:0在cffff以后，参见课本12页（第二版）可知这里属于ROM地址空间是不能修改的
(2)不对，因为机子刚启动调用int 19h中断时操作系统还没起来，还没有加载操作系统相应的中断程序，所以不能由dos提供int 19h