SectorsTable[FileHandle]=(300, 4, 46, 35, ....)

 TForm1=...
 public
  function ReadThread1Execute(Sender: PThread): Integer;
  function ReadThread2Execute(Sender: PThread): Integer;
 end;

var
 ReadThread1, ReadThread2 : PThread;
...
function TForm1.ReadThread1Execute(Sender: PThread): Integer;
var
S : PStream;
begin
S := NewReadFileStream('blablabla.gfc');
S.Position := 0;
цикл отS.Position до определенного места файла;

Free_And_Nil(S);
ReadThread1.Terminate;
end;

function TForm1.ReadThread2Execute(Sender: PThread): Integer;
var
S : PStream;
begin
S := NewReadFileStream('blablabla.gfc');
S.Position := определенное место файла;
цикл от S.Position до конца файла;
Free_And_Nil(S);
ReadThread2.Terminate;
end;

procedure TForm1.Button1Click(Sender: PControl);
begin
ReadThread1 := NewThreadAutoFree(Form1.ReadThread1Execute);
ReadThread2 := NewThreadAutoFree(Form1.ReadThread2Execute);
ReadThread1.Resume;
ReadThread2.Resume;
repeat
 ReadThread1.WaitForTime(1000);
until ReadThread1.Terminated and ReadThread2.Terminated;
Free_And_Nil(ReadThread2);
Free_And_Nil(ReadThread1);
end;

TForm1=...
public
 function ReadThread1Execute(Sender: PThread): Integer;
 function ReadThread2Execute(Sender: PThread): Integer;
end;

var
ReadThread1, ReadThread2 : PThread;
R1Stop, R2Stop : boolean;

function TForm1.ReadThread1Execute(Sender: PThread): Integer;
begin
pb1.MaxProgress := 1000;
pb1.Progress := 0;
repeat
 Form1.pb1.Progress := Form1.pb1.Progress + 1;
 Form1.pb1.ProcessMessages;
until Form1.pb1.Progress >=  Form1.pb1.MaxProgress;

R1Stop := true;
ReadThread1.Terminate;
end;

function TForm1.ReadThread2Execute(Sender: PThread): Integer;
begin
pb2.MaxProgress := 10000;
pb2.Progress := 0;
repeat
 pb2.Progress := pb2.Progress + 1;
 pb2.ProcessMessages;
until pb2.Progress = pb2.MaxProgress;

R2Stop := true;
ReadThread2.Terminate;
end;

procedure TForm1.Button1Click(Sender: PObj);
begin
R1Stop := false;
R2Stop := false;
ReadThread1 := NewThreadEx(Form1.ReadThread1Execute);
ReadThread1.Resume;

ReadThread2 := NewThreadEx(Form1.ReadThread2Execute);
ReadThread2.Resume;
repeat
 Form1.Form.ProcessMessages;
until R1Stop and R2Stop;
Free_And_Nil(ReadThread2);
Free_And_Nil(ReadThread1);
end;

repeat
 Form1.Form.ProcessMessages;
until R1Stop and R2Stop;