Before downloads became the norm, software was sold on physical storage media, such as CDs or disks, from which the programs could be installed and launched. But since these media were often copied or lent out to friends or acquaintances, software manufacturers began assigning individual numbers to every copy sold. This ensured that software could only be used once the purchased product key had been entered.
But with the majority of software now available for download, the days of printed product keys on CD sleeves are long gone. Because operating systems come preinstalled when you purchase a desktop or laptop computer, you no longer need to make note of a product key to get started. However, if your hard disk requires formatting because of malware or for performance reasons, you will need to enter the product key during the Windows 7 reinstallation, in order to be able to use the operating system.