uses System.Classes, System.SysUtils,
  System.Generics.Collections;

var
  Dic: TDictionary<Integer, string>;
  Pair: TPair<Integer, string>;
  Writer: TBinaryWriter;
begin
  Dic := TDictionary<Integer, string>.Create;
  Dic.Add(1, 'one');
  Dic.Add(2, 'two');

  Writer := TBinaryWriter.Create(
    'data.bin', False);
  try
    Writer.Write(Dic.Count);
    for Pair in Dic do
    begin
      Writer.Write(Pair.Key);
      Writer.Write(Pair.Value);
    end;
  finally
    Writer.Free;
  end;

  WriteLn('data written to file');
end.