新手请教为何 API函数编程 速度太慢

如题,以下是代码:
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  hFile: THandle;
  iLen: LongWord;
  Buffer: AnsiString;
  SizeDisk: int64;
  FreeSize: int64;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  FreeSize := DiskFree(4); //获取D:可用空间
  Buffer := '00000000'; //一个字节的0
  hFile := CreateFile('D:\Data.dat',
                      GENERIC_WRITE,
                      0,
                      Nil,
                      CREATE_ALWAYS,
                      FILE_ATTRIBUTE_NORMAL  ,
                      0);
  if (hFile = INVALID_HANDLE_VALUE) then
    begin
      MessageBox(GetActiveWindow(),'创建文件失败!',Nil,MB_OK or MB_ICONERROR);
      Exit;
    end;
  SetFilePointer(hFile,1,NIL,FILE_BEGIN);
  WrITeFile( hFile, Buffer[1], Length(Buffer), iLen, Nil);
  while FreeSize>0 do
    begin
      FreeSize:=FreeSize-1;
      SetFilePointer(hFile,1,NIL,FILE_CURRENT);
      WrITeFile( hFile, Buffer[1], Length(Buffer), iLen, Nil);
    end;
  CloseHandle(hFile);
end;

end.


[ 本帖最后由 tomsen1968 于 2010-4-4 12:01 编辑 ]