Branded OS discs are special discs designed to work with that brand of computer.  In most cases, it is for simplicity and ease of activation - Dell discs will work on HP machines, but will NOT activate Windows, because it is not a Dell computer; HP discs will usually NOT work on any other brand - or even model - than it was designed for.  A Dell installation disc will automatically activate Windows when installed on a Dell; HP on an HP.  Dell installation discs are fairly "clean" ... they do NOT include drivers or any factory-installed software - they contain ONLY Windows installation files, as found on a regular retail Windows disc, with the addition of some Dell branding information (Dell backgrounds, user account pictures, support badge, etc.).

For Windows 7 the Dell branded OEM Reinstallation DVD has a system Locked Preinstallation Key and activation mechanism inbuilt.

If the correct BIOS is available it will activate i.e. if a Dell BIOS is present which Dell have certified for Windows 7. It will not activate on any other brand of computer. Sometimes the installation DVDs are sold with a COA however and activation can be carried out by inputting the key on the COA and phoning Microsoft. Dell OEM Reinstallation DVDs and COAs may not be legal without being provided with Dell hardware.

Users should not use Dell Reinstallation DVDs on a non-Dell. They should instead look to a generic system builders OEM Windows 7 license or retail license. The OEM license/system builders license has the drawback that it is tied to the original machine, in particular the motherboard and cannot be transferred from computer to computer. Also in most cases the OEM has to provide support opposed to Microsoft. It is cheaper however.