Among the components of the mechanical disk, the parts responsible for reading and writing data are:

The read/write head is the core component responsible for the data transfer process in a mechanical hard disk drive (HDD). It is a tiny transducer that floats nanometers above the spinning platter's surface. To write data, it generates a precise magnetic field to alter the magnetic orientation of particles on the platter. To read data, it detects the existing magnetic fields from the platter and converts them back into electrical signals. The other listed components are essential for the drive's operation but do not perform the actual reading or writing.

A. Disc: Also known as a platter, this is the physical medium where data is magnetically stored, but it does not actively read or write the data itself.
C. Magnetic head arm: This component, also called an actuator arm, positions the read/write head over the correct data track on the platter but is not the transducer.
D. Spindle: This is a motor that rotates the platters at a constant, high speed, allowing the read/write head to access different parts of the disk.

1. Huawei Certified ICT Associate (HCIA) - Storage. (2023). H13-611 HCIA-Storage V5.0 Training Material. Section 2.1.1, "HDD Components and Working Principles," describes the read/write head as the component that "reads data from and writes data to disks."

2. Patterson, D. A., & Hennessy, J. L. (2017). Computer Organization and Design: The Hardware/Software Interface (5th ed.). Morgan Kaufmann. Chapter 5, "Large and Fast: Exploiting Memory Hierarchy," Section 5.4, describes the mechanics of magnetic disks, stating, "The heads are the devices that read and write the information on the disk."

3. Arpaci-Dusseau, R. H., & Arpaci-Dusseau, A. C. (2018). Operating Systems: Three Easy Pieces. Arpaci-Dusseau Books. Chapter 37, "Hard Disk Drives," Section 37.2, "The Interface," explains, "To read or write, the head must be positioned at the desired track... Once the head is at the right track, the system waits for the desired sector to rotate under the read/write head." This clarifies the distinct roles of the head and the positioning/rotation mechanisms.