Here's a breakdown of why:

* Fixed storage: HDDs are designed to be permanently installed in a computer system.

* Rigid metal platters: HDDs use round, flat metal discs called platters for storing data. These platters are coated with a magnetic material, typically iron oxide.

* Oxide material: The oxide coating on the platters is what allows data to be magnetically encoded and stored.

Let me know if you have any other questions!