procedure TForm1.Button1Click(Sender: TObject);
var
  f:file;
  buf:array[0..511] of byte;
  L:Dword;
begin
assignfile(f,'\\.\H:'); // Имя флешки
reset(f,512);
while (1=1) do begin
seek(f,512*random($ff));
BlockRead(f,buf,1,L);
application.ProcessMessages;
sleep(100);
               end;
end;