Computer hard disks store changing digital information in a relatively permanent godway computer disk store format, and are an essential component of almost all desktop and laptop computers.
Your average hard drive contains one or more metal or glass or ceramic platters, each spinning along its axis at a rate of 5,400-7,200 rpm, and carefully storing binary 1s and 0s — coded 1s and 0s — that constitute files. Spinning the platters is one motor, and regulating the read/write heads that magnetise and read the data on each of the platters is another.
Read/Write Heads
Read/Write Heads are (physical constituents of hard disks) Moving over the surface of platters that convert magnetic field into electrical current in other words read/write Goes from electrical polarity of very small particles in the surface of disk (thin ferromagnetic coating protected)
To read those heads, writes head read magnetic polarity to tell which polarity bears either 1 or 0 inside each bit. Drives use logic boards to write data, dispatching small currents to actuator arms that adjust magnetic polarity of heads.
If an engineer wants to control how the head is positioned to an arbitrary degree of accuracy, so that it can read or write a single segment of the disk, then the most robust way to do this is to keep it under control via a voice coil actuator.
Platters
Drives (disks) are plates of metal coated with micron-thin layers of magnetic material mounted by spindles to turn with high RPMs and tracking heads floating directly above each platter reading or writing data magnetically.
Every plate consists of a series of concentric circles known as tracks and sectors. Sets of 0s and 1s are imprinted on each track and read by an electromagnet that sweeps coiled wire over the surface of the disk, magnetising at spots that represent zeros and ones.
Modern drives have Voice Coil Motor (VCM) controls of actuator arm movement between disk surfaces in a closed loop (replacing open loop actuators using cable and pulleys with VCM controlled closed loop) control.
Spindle
Spindle motors in hard drives try to maintain platters at a uniform speed by creating a magnetic field in an electromagnet on their stator assembly.
This force is passed to the spindle via its shaft. Then, read/write heads are driven across platter(s) according to firmware by means of voice coil actuator arms.
In fact, modern HDDs have two shock sensors designed to detect sudden impacts or vibrations with their MCU processing the amplitude and duration. Upon receipt of one of these alerts, the drive will take immediate action (using its drive head actuator) to park its drive heads – and minimise the likelihood of irreversible damage.
The service area of a disk contains modules of embedded software, such as a translation table that maps operating system logical block addressing into physical block addressing on the device. It also contains components that store adaptive data produced by manufacturers during the manufacturing process.
Actuator Arm
Data are read or written as the actuator arm swings read/write heads across each platter. Each head floats atop an actuator arm, all moved together across each platter.
The arms move under the influence of a Lorentz force, where the passage of current through coils generates magnetic fields around them that cause them to be pulled in to or away from a permanent magnet (depending on which coil has how much current passing through it) – and you mechanically alter the amount of current passing through a given coil at any one time in order to make this drive the arms around in a random but controllable way.
Arm motions had to be timed to the nanosecond to keep data on the platters from flying off, making highly accurate, rapid-response locator arms all the more necessary to identify sectors at spin speeds of up to 15,000 RPMs.
PCB
The PCB (Printed Circuit Board) controls power to the drive, controls data flows, contains the calibrations that allow the motors to function optimally and tracks wear leveling and error correction tasks, most of which are easier with firmware.
It has a controller chip to read or write data to the physical disk platters, arrange each part of the disk into sectors for reallocated use, and perform maintenance functions such as sector reallocation. A motor control chip resides on the PCB to make sure the platters spin at a constant speed to facilitate data access.
Before now however, PCBs were relatively exchangeable between different models of a brand’s hard drives. But as technology advances, swapping PCBs is becoming less practical, and any attempts can result in permanent data destruction.
