BIOS has never been store in HDD since first day of personal computing It is stored in EEPROM on the motherboard.

Unlike before where when we purchased PC or laptop, we are provided with Windows CD and mobo drivers CD, nowadays the installation CD is stored on HDD in image form partitioned separately. Therefore when your Windows gets corrupted, you will be asked if you want to format and reinstall the Windows. The PC will automatically reinstall the Windows itself from this partition (unless the HDD itself failed). Therefore it is advisable to create another partition to store all your documents. Re-installation will format only C:\ drive.