File Comparison

I think this is what you need...
code could be optimized..

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Memo1: TMemo;
    OpenDialog1: TOpenDialog;
    OpenDialog2: TOpenDialog;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
    fname1,fname2:string;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
begin
  if opendialog1.execute then fname1:=opendialog1.filename;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  if opendialog2.execute then fname2:=opendialog2.filename;
end;

procedure TForm1.Button3Click(Sender: TObject);
var s1,s2:Tfilestream;
    i,j:integer;
    a,b:byte;
begin
  s1:=tfilestream.Create(fname1,fmOpenRead);
  s2:=tfilestream.Create(fname2,fmOpenRead);

  if s1.Size > s2.size then i:=s2.size else i:=s1.size;

  For j:=1 to i-1 do
  Begin
    s1.Read(a,1);
    s2.Read(b,1);
    if a<>b then memo1.lines.add(inttohex(j,6)+'  '+inttohex(a,2)+' '+inttohex(b,2));
  End;

  if s1.Size > s2.size then memo1.Lines.add(fname1+' is lager than '+fname2);
  if s1.Size < s2.size then memo1.Lines.add(fname2+' is lager than '+fname1);

  s1.free;
  s2.free;
end;

end.