Código Delphi [-]
begin
  AssignFile(myFile, 'C:\Temp\SELE-SAL-CONSTA.tmp');
  i:=0;
  FileMode := fmOpenRead;
  Reset(myFile);
  Memory.Active:=true;
  while not Eof(myFile) do
  begin
    text:='';
    while length(text) < 21 do
    begin
      Read(myFile, letter) ;   // Read and display one letter at a time
      text:=text + letter ;
    end;
    Read(myFile, letter);
    Memory.Append;
    Memorycuil.Value :=copy(text,1,2)+'-'+copy(text,3,8)+'-'+copy(text,11,1);
    Memoryganancias.Value:=copy(text,12,2);
    Memoryiva.Value:=copy(text,14,2);
    Memorymonotibuto.Value:= copy(text,16,2);
    MemoryintegranteSo.Value:= copy(text,18,1);
    Memoryempleador.Value:=copy(text,19,1);
    MemoryactividadMono.Value:=copy(text,20,2);
    Memory.Post;
    i:=i+1;
    Label1.Caption:=inttostr(i);
  end;
end;

Código Delphi [-]
procedure TForm1.Button2Click(Sender: TObject);

var
  Fichero: File of byte;
  Buffer: array[0..21] of Char; // 22 bytes + 1
  Leidos: Integer;
  Str: string;
  b:byte;
  i:integer;
begin
i:=0;
  AssignFile(Fichero,'C:\Temp\SELE-SAL-CONSTA.tmp');
  Filemode:= fmOpenRead;
   Memory.Active:=true;
  {$I-}
    Reset(Fichero);// Reset(Fichero,1);
  {$I+}
  Timer1.Enabled:= true;
  if IOResult = 0 then
  begin

    while not  eof(Fichero) do
    begin
      FillChar(Buffer,Sizeof(Buffer),0);
      BlockRead(Fichero,Buffer,Sizeof(Buffer)-1,Leidos);
      read(fichero,b);
      if Leidos > 0 then
      begin
        Str:= String(PChar(@Buffer));
         i:=i+1;
         Label1.Caption:=inttostr(i);
        CargarGrilla(Str);
      end;
    end;
    Timer1.Enabled:=false;
    CloseFile(Fichero);
  end else
    ShowMessage('No puedo abrir el archivo');
end;

Código Delphi [-]
...
const
  NCHAR = 22;
  LEER_X = 20000 ;
  TOT_BUFFER = LEER_X * NCHAR;

procedure TForm1.btnACDSClick(Sender: TObject);
var
  F: file of Char;
  Buf: array[1..TOT_BUFFER] of Char;
  c, rl: Integer;
  T1,T2: TTime;
  Ciclos: Integer;
begin
  AssignFile(F, 'C:\Archivo.txt');
  try
    Reset(file(F), 1);
    ClientDataSet.CreateDataSet;
    ClientDataSet.Open;
    ClientDataSet.DisableControls;
    T1:= Time;
    Ciclos:= 1;
    repeat
      BlockRead(file(F), Buf, SizeOf(Buf), rl);
      c:= 0;
      while c < TOT_BUFFER do
      begin
        if c mod 100 = 0 Then 
          ClientDataSet.MergeChangeLog;
        ClientDataSet.Append;
        ClientDataSetCuit.AsString:= Buf[c+1]+Buf[c+2]+Buf[c+3]+
            Buf[c+4]+Buf[c+5]+Buf[c+6]+Buf[c+7]+Buf[c+8]+Buf[c+9]+
            Buf[c+10]+Buf[c+11];
        ClientDataSetD1.AsString:= Buf[c+12]+Buf[c+13];
        ClientDataSetD2.AsString:= Buf[c+14]+Buf[c+15];
        ClientDataSetD3.AsString:= Buf[c+16]+Buf[c+17];
        ClientDataSetD4.AsString:= Buf[c+18];
        ClientDataSetD5.AsString:= Buf[c+19];
        Inc(c, NCHAR);
        ClientDataSet.Post;
      end;
      Inc(Ciclos);
    until rl = 0;
    CloseFile(F);
    T2:= Time;
    Caption:= FormatDateTime('hh:mm:ss:dd',T2-T1)+'  realizando '+IntToStr(Ciclos)+' ciclos.';
    ClientDataSet.EnableControls;
  except
    ShowMessage('Archivo inexistente');
  end;
end;