Alternatively referred to as read/write head arm, head arm, or actuator arm, the access arm is in every mechanical hard drive; similar in appearance to the arm of a record player. As the platter spins, the access arm adjusts the read/write heads to facilitate the reading, writing, or deletion of information.
One or more aluminum, glass, or ceramic disk that is coated in a magnetic media and is located within a hard drive to permanently store all your computer's data. When the computer is turned on, these platters will begin to rotate at so many RPM (rotations per minute). This rate varies depending on the model of hard drive you have; an example of how fast a hard drive may spin is 7200 RPM. As the disk platters are rotating, the read/write head accesses information on one of the platters.
The heart of PCB is the biggest chip in the middle called Micro Controller Unit or MCU. On modern HDDs MCU usually consists of Central Processor Unit or CPU which makes all calculations and Read/Write channel - special unit which converts analog signals from heads into digital information during read process and encodes digital information into analog signals when drive needs to write. MCU also has IO ports to control everything on PCB and transmit data through SATA interface.