What is the part in the cumputer that holds information in the cumputer that is held in a magnetic cilinder?

The component you are referring to is likely the hard disk drive (HDD). In an HDD, data is stored on magnetic platters that spin within a sealed casing. Information is written to and read from these platters using read/write heads that move across the surfaces, allowing for the storage of large amounts of data in a non-volatile format.