There is no such thing as a ''Dell Computer". The whole system is built of parts badged up as Dell.
Your hard drive isn't Dell because they dont make hard drives, they install a WD or a Samsung or a Seagate or whatever they have bulk purchased at the time.
Your optical drive will have a Dell badge on it but likewise they dont make optical drives ... Sony,Samsung, etc do.
So your whole system is created from various parts from various suppliers The system is built to Dell standards thats all. ... and nearly all parts are interchangeable and upgradeable, depending on specifications.