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procedure TForm1.Button1Click(Sender: TObject);
  var st: TMemoryStream;
      s: string;
  begin
    s := Memo2.Text;
    st := TMemoryStream.Create;
    try
      st.WriteBuffer(s,length(s));
      IdFtp1.Connect;
      IdFtp1.put(st, 'instructions.dat');
    finally
      IdFtp1.Quit;
      st.Free;
    end;
  end;

procedure TForm1.Button2Click(Sender: TObject);
  var st: TMemoryStream;
      s: string;
  begin
    st := TMemoryStream.Create;
    try
      IdFtp1.Connect;
      IdFtp1.Get('instructions.dat',st);
      st.Seek(0, soFromBeginning);
      st.ReadBuffer(s,st.Size);
      Memo1.Text := s;
    finally
      IdFtp1.Quit;
      st.Free;
    end;
  end;

procedure TForm1.Button3Click(Sender: TObject);
  var  st: TMemoryStream;
        s: string;
  begin
    s := Memo2.Text;
    st := TMemoryStream.Create;
    try
      st.WriteBuffer(s,length(s));
      st.Seek(0, soFromBeginning);
      st.ReadBuffer(s,st.Size);
      Memo1.Text := s;
    finally
      st.Free;
    end;
  end;

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st.WriteBuffer(PChar(s)^, Length(s));