Uses Crt,Dos;
Var C:Word;Regs:Registers;
Begin
For C:=0 to 3999 do Mem[$B800:C]  := 10;
For C:=0 to 4202 do Mem[$B800:C+4000]  := 20;
ReadKey;
Regs.AH:=5;
Regs.AL:=1;
Intr($10,Regs);
ReadKey;
Regs.AL:=2;
Intr($10,Regs);
Readkey;
Regs.AL:=0;
Intr($10,Regs);
Readkey;
End.