BY JOSH ALBA
A hard disk is the computers main memory source.
How a Hard Drive works in Slow Motion - The Slow Mo Guys
how it works
Nearly every desktop computer and server in use today contains one or more hard-disk drives. Everymainframe and supercomputer is normally connected to hundreds of them. You can even find VCR-type devices and camcorders that use hard disks instead of tape. These billions of hard disks do one thing well -- they store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.
3D Animation - How The Harddrive Works