add new interrupt

os.asm

@@ -36,7 +36,7 @@ start:
 
         mov si,int_0x20 ; SI now points to int_0x20 
         mov di,0x0020*4 ; Address of service for int 0x20
-        mov cl,7
+        mov cl,8
 .load_vec:
         movsw           ; Copy IP address
         stosw           ; Copy CS address
@@ -489,6 +489,7 @@ int_0x20:
         dw save_file        ; int 0x24
         dw delete_file      ; int 0x25
 	dw input_line	    ; int 0x26
+	dw 0x7a00	    ; int 0x27
 
 error_message:
 	db 0x13