Final answer:
The round, thin plates of metal within a hard drive are called platters, which store data magnetically and are accessed using technologies like giant magnetoresistance.
Step-by-step explanation:
The round, thin plates of metal within a hard drive are known as platters. These platters are the core components of a hard disk drive (HDD) where data is stored magnetically. Covered with a magnetic coating, they spin at high speeds while a read/write head moves across them to access or record data. They are essential for the HDD's functionality, which has historically been based on the principle of magnetic induction. However, most modern hard drives have advanced to using a technology known as giant magnetoresistance (GMR). This allows for the reading and writing of the digital information that computers use, represented by a series of 0's and 1's, with greater sensitivity and less electrical resistance.