uses crt;
var M,N : Integer;
type
    MyType = Integer;
type
    MyMatrix = array [1..1,1..1] of MyType;
    TMatrix = ^MyMatrix;

{-----------------------------------------------}
Procedure ReadMatrix(var mx : TMatrix);
var i,j : Integer;
begin
     for i := 1 to M do
        for j := 1 to N do begin
           Write('Element [',i,',',j,']:');
           ReadLn(mx^[i,j]);
        end;
end;
{-----------------------------------------------}

{-----------------------------------------------}
Procedure WriteMatrix(var mx : TMatrix);
var i,j : Integer;
begin
     for i := 1 to M do
        for j := 1 to N do begin
           Write(mx^[i,j]:3);
           if j = N then WriteLn;
        end;
end;
{-----------------------------------------------}

var a : TMatrix;
    Size : Word;

begin
     {$R-}
     Clrscr;
     Write('Input M:');
     ReadLn(M);
     Write('Input N:');
     ReadLn(N);
     Size := M * N * SizeOf(MyType);
     GetMem(a,Size);
     WriteLn('Input Matrix:');
     ReadMatrix(a);
     WriteLn;
     WriteLn('Source Matrix:');
     WriteMatrix(a);
     FreeMem(a,Size);
     Readkey;
end.

GetMem(a,Size);

type
  MyType = Integer;
  PVector = ^TVector;
  TVector = Array[1 .. maxInt div sizeof(MyType)] Of MyType;

  PMatrix = ^TMatrix;
  TMatrix = Array[1 .. MaxInt div sizeof(PVector)] Of PVector;

  ReadLn(M);
  GetMem(a, M*SizeOf(PVector));
  ReadLn(N);
  For i := 1 To M Do
    GetMem(a^[i], N*SizeOf(MyType));

Procedure WriteMatrix(mx : PMatrix);
var i, j : Integer;
begin
  for i := 1 to M do begin
    for j := 1 to N do
      Write(mx^[i]^[j]:3);
    WriteLn;
  end;
end;

MaxInt div sizeof(Type)

выводит правильно, но вместо того чтобы ждать нажатия клавиши (Readkey), выдает Runtime - error 204...

  For i := 1 To M Do
    FreeMem(a^[i], N*SizeOf(MyType));
  FreeMem(a, M*SizeOf(PVector));

MaxInt div sizeof(Type)

TVector = Array[1 .. 2 * maxInt div sizeof(MyType)] Of MyType;

type
  ...
  TVector = Array[1 .. 1] Of MyType;
  ...
  TMatrix = Array[1 .. 1] Of PVector;

  For i := 1 To M Do
    FreeMem(a^[i], N*SizeOf(MyType));
  FreeMem(a, M*SizeOf(PVector));

FreeMem(a, M*SizeOf(PVector));
For i := 1 To M Do
    FreeMem(a^[i], N*SizeOf(MyType));

FreeMem(a, M*SizeOf(PVector));
For i := 1 To M Do
    FreeMem(a^[i], N*SizeOf(MyType));

GetMem(x1, ...);
GetMem(x2, ...);
...

...
FreeMem(x2, ...);
FreeMem(x1, ...);