type
  TRec1 = record
    a: Cardinal;
    b: Word;
    c: Byte;
  end;

  TRec2 = packed record
    a: Cardinal;
    b: Word;
    c: Byte;
  end;

procedure TForm1.Button1Click(Sender: TObject);
const
  CCount = 100000000;
var
  LArr1: array of TRec1;
  LArr2: array of TRec1;
  LSum: Cardinal;
  Li: Integer;
  LStart: Cardinal;
  LDrtn1, LDrtn2: Cardinal;
begin
  LStart := GetTickCount;
  LSum := 0;
  SetLength(LArr1, CCount);
  for Li := 0 to CCount - 1 do begin
    LArr1[Li].a := Random(High(LArr1[Li].a));
    LArr1[Li].b := Random(High(LArr1[Li].b));
    LArr1[Li].c := Random(High(LArr1[Li].c));
    LSum := LSum + LArr1[Li].a + LArr1[Li].b + LArr1[Li].c;
  end;
  LDrtn1 := GetTickCount - LStart;
  SetLength(LArr1, 0);

  LStart := GetTickCount;
  LSum := 0;
  SetLength(LArr2, CCount);
  for Li := 0 to CCount - 1 do begin
    LArr2[Li].a := Random(High(LArr2[Li].a));
    LArr2[Li].b := Random(High(LArr2[Li].b));
    LArr2[Li].c := Random(High(LArr2[Li].c));
    LSum := LSum + LArr2[Li].a + LArr2[Li].b + LArr2[Li].c;
  end;
  LDrtn2 := GetTickCount - LStart;
  SetLength(LArr2, 0);
  ShowMessageFmt('NonPacked: %u, Packed: %u, Delta: %.2f%%', [LDrtn1, LDrtn2, 100 - LDrtn1 * 100 / LDrtn2]);
end;