Registry

Data File for OS to Hardware/Drivers:

The Registry is a database of all the settings and locations of 32-bit drivers in the system. When the OS needs to access hardware devices, it uses drivers, even if the device is a BIOS-supported device. Non-BIOS-supported devices that are installed must also have a driver. The drivers are independent of the OS, but the OS needs to know where to find them, the filename, the version, and other settings and information. Without Registry entries for each of the devices, they would not be usable.

Data File for OS to Applications:

When a user attempts to launch an application, the Registry supplies application information to the OS so the application can be found, the correct data file locations are set, and other settings are available. The Registry holds information about default data and auxiliary file locations, menus, button bars, window status, and other options. It also holds installation information such as the date of installation, the user who installed the software, the version number and date, and sometimes the serial number.
Depending on the actual software installed, it may contain other application-specific information.