Installing Windows 8 in new hard drive

Hi Guys,
Most of the laptops now comes with Windows 8 pre-installed but the license key is not on the laptops anymore. I guess, the key is stored somewhere in BIOS but it is impossible to read it. So what I want to know if I need the product key to download Windows 8 from Microsoft? Does anybody have some insights about it? Anyone can help? Thank you.
