type

 t1 = record
 b: byte;
 end;

 t2 = record
 w: word;
 end;

 t4 = record
 d: dword;
 end;

 t8 = record
 i: int64;
 end;

 t9 = record
 i: int64;
 b: byte;
 end;

 t10 = record
 i: int64;
 w: word;
 end;

 t12 = record
 i: int64;
 d: dword;
 end;

 t16 = record
 i: int64;
 i2: int64;
 end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 Edit1.Text:=Format('%d %d %d %d %d %d %d %d',
 [SizeOf(t1), SizeOf(t2), SizeOf(t4), SizeOf(t8),
  SizeOf(t9), SizeOf(t10), SizeOf(t12), SizeOf(t16)]);
end;

Type
TRec1=Record
 a:Int64;
 b:Byte;
 c:Integer;
 d:Byte;
End;

TRec2=Record
 a:Int64;
 b:Byte;
 d:Byte;
 c:Integer;
End;

Move(r1,abc,SizeOf(t1)); //тут скопируется 1 байт
Move(r5,abc,SizeOf(t5)); //тут скопируется 8 байт, а не 5, как ожидаю я

 t44 = record
 i1: int64;
 i2: int64;
 i3: int64;
 i4: int64;
 d1: dword;
 d2: dword;
 d3: dword;
 end;

If two fields share a common type specification, they are packed even if the declaration does not include the packed modifier and the record type is not declared in the {$A-} state. Thus, for example, given the following declaration
type
 TMyRecord = record
   A, B: Extended;  
   C: Extended;
 end;
A and B are packed (aligned on byte boundaries) because they share the same type specification. The compiler pads the structure with unused bytes to ensure that C appears on a quadword boundary.

unit SizeOfU2;

interface

type
 TMy1= integer;
 TMy2= record
   pref: int64;
   i2: integer;
   end;

implementation

end.

uses
 SizeOfU2;

procedure TForm1.Button1Click(Sender: TObject);
var
 i1: TMy1;
 i2: TMy2;
begin
Edit1.Text:=Format('%d %d',
[SizeOf(TMy1), SizeOf(TMy2)]);
end;

type
 T1n= record
   a: byte;
   end;
 T1p= packed record
   a: byte;
   end;
 T2n= record
   a: integer;
   b: byte;
   end;
 T2p= packed record
   a: integer;
   b: byte;
   end;

 T11nn= packed record
   a: T1n;
   b: T1n;
   end;
 T11np= packed record
   a: T1n;
   b: T1p;
   end;
 T11pn= packed record
   a: T1p;
   b: T1n;
   end;
 T11pp= packed record
   a: T1p;
   b: T1p;
   end;

 T21nn= packed record
   a: T2n;
   b: T1n;
   end;
 T21np= packed record
   a: T2n;
   b: T1p;
   end;
 T21pn= packed record
   a: T2p;
   b: T1n;
   end;
 T21pp= packed record
   a: T2p;
   b: T1p;
   end;

 T22nn= packed record
   a: T2n;
   b: T2n;
   end;
 T22np= packed record
   a: T2n;
   b: T2p;
   end;
 T22pn= packed record
   a: T2p;
   b: T2n;
   end;
 T22pp= packed record
   a: T2p;
   b: T2p;
   end;

 N11nn= record
   a: T1n;
   b: T1n;
   end;
 N11np= record
   a: T1n;
   b: T1p;
   end;
 N11pn= record
   a: T1p;
   b: T1n;
   end;
 N11pp= record
   a: T1p;
   b: T1p;
   end;

 N21nn= record
   a: T2n;
   b: T1n;
   end;
 N21np= record
   a: T2n;
   b: T1p;
   end;
 N21pn= record
   a: T2p;
   b: T1n;
   end;
 N21pp= record
   a: T2p;
   b: T1p;
   end;

 N22nn= record
   a: T2n;
   b: T2n;
   end;
 N22np= record
   a: T2n;
   b: T2p;
   end;
 N22pn= record
   a: T2p;
   b: T2n;
   end;
 N22pp= record
   a: T2p;
   b: T2p;
   end;

procedure TForm1.Button1Click(Sender: TObject);
begin
Memo1.Lines.Add(Format('T1n=%d T1p=%d',
[SizeOf(T1n), SizeOf(T1p)]));

Memo1.Lines.Add(Format('T2n=%d T2p=%d',
[SizeOf(T2n), SizeOf(T2p)]));

Memo1.Lines.Add(Format('T11nn=%d T11np=%d T11pn=%d T11pp=%d',
[SizeOf(T11nn), SizeOf(T11np), SizeOf(T11pn), SizeOf(T11pp)]));

Memo1.Lines.Add(Format('T21nn=%d T21np=%d T21pn=%d T21pp=%d',
[SizeOf(T21nn), SizeOf(T21np), SizeOf(T21pn), SizeOf(T21pp)]));

Memo1.Lines.Add(Format('T22nn=%d T22np=%d T22pn=%d T22pp=%d',
[SizeOf(T22nn), SizeOf(T22np), SizeOf(T22pn), SizeOf(T22pp)]));

Memo1.Lines.Add(Format('N11nn=%d N11np=%d N11pn=%d N11pp=%d',
[SizeOf(N11nn), SizeOf(N11np), SizeOf(N11pn), SizeOf(N11pp)]));

Memo1.Lines.Add(Format('N21nn=%d N21np=%d N21pn=%d N21pp=%d',
[SizeOf(N21nn), SizeOf(N21np), SizeOf(N21pn), SizeOf(N21pp)]));

Memo1.Lines.Add(Format('N22nn=%d N22np=%d N22pn=%d N22pp=%d',
[SizeOf(N22nn), SizeOf(N22np), SizeOf(N22pn), SizeOf(N22pp)]));
end;

T1n=1 T1p=1
T2n=8 T2p=5
T11nn=2 T11np=2 T11pn=2 T11pp=2
T21nn=9 T21np=9 T21pn=6 T21pp=6
T22nn=16 T22np=13 T22pn=13 T22pp=10
N11nn=2 N11np=2 N11pn=2 N11pp=2
N21nn=12 N21np=12 N21pn=6 N21pp=6
N22nn=16 N22np=16 N22pn=16 N22pp=10

the largest alignment of the fields in the record

t9 = record
i: int64;
b: byte;
end;

t1 = record
b: byte;
end;

tt1 = record
b: byte;
b2: byte;
end;

tt2 = record
b: integer;
b2: byte;
end;

tt2 = record
b: integer;
b2: byte;
end;

the largest alignment of the fields in the record

tt1 = record
c: integer;
b2: int64;
c1: integer;
end;

tt1 = record
c: integer;
b2: int64;
c1: byte;
c2: byte;
end;

tt1 = record
b2: int64;
c1: byte;
w: integer;
c2: byte;
end;

t9 = record
 i: int64;
 b: byte;
 end;

procedure TForm1.Button1Click(Sender: TObject);
var
 t: t9;
begin
 ShowMessage(IntToStr(pchar(@t.b)-pchar(@t.i)));
end;

{$A8}
TMR1=Record
 a:Byte;
 // - щель 1b
 c:Word;
 d:Byte;
 // - щель 1b
 e:Word;
End; // 8b

TMR2=Record
 a:Byte;
 // 1b
 c:Word;
 // 2b
 d:Byte;
 // 3b
 e:Integer;
End; // 12b

хотя

{$A2}
TMR1=Record
 a:Byte;
 // - щель 1b
 c:Word;
 d:Byte;
 // - щель 1b
 e:Word;
End; // 8b

TMR2=Record
 a:Byte;
 // 1b
 c:Word;
 // 2b
 d:Byte;
 // 1b
 e:Integer;
End; // 10b

{$A2}
TMR2=Record
a:Byte;
// 1b
c:Word;
d:Byte;
// 1b
e:Integer;
End; // 10b

{$A8}
TMR1=Record
 a:Byte;
 "просвет" 1b
 c:Word;
 d:Byte;
 "просвет" 1b
 e:Word;
End; 8b

TMR2=Record
 a:Byte;
 "просвет" 1b
 c:Word;
 d:Byte;
 "просвет" 3b
 e:Integer;
End; 12b

{$A2}
TMR1=Record
 a:Byte;
 "просвет" 1b
 c:Word;
 d:Byte;
 "просвет" 1b
 e:Word;
End; 8b

TMR2=Record
 a:Byte;
 "просвет" 1b
 c:Word;
 d:Byte;
 "просвет" 1b
 e:Integer;
End; 10b