The most common form factors of hard drive are 3.5 and 2.5 inch.
The hard disks are used widely in personal computers, laptops, netbooks, tablet computers, servers, and so on.
What is hard drive? In a semi-hermetic unit there are bilateral platters coated with a magnetic layer. The platters sit on a motor spindle and rotate at a speed of 5400 or 7200 rpm. The unit is not quite tight, but the most important thing is that it prevents fine particles from penetrating inside it and is waterproof. All this adversely affects the lifespan and quality of work of the hard drive.
In modern hard drives, hydrodynamic bearings are used for the shaft. They are less noisy during operation, greatly increases durability and reduces the chance of jamming the shaft due to the destroying of the rolling bearing.
Reading and writing is performed by the head assembly.
When in use, the heads floating above the surface of the disk at a distance of ~ 10 nm. They have an aerodynamic shape and rise above the surface of the disk due to the upward flow of the spinning platters. Magnetic heads are located on both sides of the plate, if each side of the magnetic disk has magnetic layers.
The heads are fixed to each other so they move together. All heads are managed by special drive based on electromagnetism. Neodymium magnet creates a magnetic field in which a high reaction rate under the influence of a current can move the head stack. It is the best and fastest option to move the head assembly as compared to mechanical drive using gears.
When the drive is switched off, to the head rests on the disc and do not damage it since they are removed in the head parking area (parking zone).
It also allows without any restrictions to transport cut out hard drives. In the off position, the disc can withstand heavy impacts and is not damaged. When enabled, even a small hit at a certain angle can destroy the magnetic layer plates or damage the head at the touch of the platters.
In addition to the sealed portion hard disks have external control printed circuit board. The entire drive control electronics, memory and cache micro-controller interface located on a small circuit board on the bottom of the hard drive. Because of this, you can configure each drive individually, favorable from the point of view of its structural parameters, giving it a speed boost, or quieter operation for example.
To connect the interface and power connectors, standard PATA / SATA and Molex / Power SATA are used.