procedure TForm1.Button1Click(Sender: TObject);
var
  SerialNum : DWord;
  A,B: DWord;
  C: array [0..255] of Char;
  Buffer: array [0..255] of Char;
begin
  if GetVolumeInformation( PChar('C:\'), Buffer, 256, @SerialNum, A, B, C, 256 ) then
     Label1.Caption := IntToStr( SerialNum );
end;

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유앤아이 현지아빠 C++ 빌더용으로 포팅 합니다..

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    DWORD SerialNum;
    DWORD A,B;
    char  C[256];
    char  Buffer[256];

    if(GetVolumeInformation("C:\", Buffer, 256, &SerialNum, A, B, C, 256)) {
        Label1->Caption = IntToStr(SerialNum);
    }
}