Mechanical hard disk (HDD) is also the ordinary hard disk we often refer to. At present, most computers still use mechanical hard disks. The structure of mechanical hard disks is quite complicated, mainly composed of: disks, magnetic heads, disk shafts and control motors, head controllers, data converters, interfaces, caches, etc. And of course the circuit board and aluminum case. All the platters in the mechanical hard disk are mounted on a rotating shaft, and each platter is parallel to each other. There is a magnetic head on the storage surface of each platter, and the distance between the magnetic head and the platter is smaller than the length of a hair The diameter is still small, all the magnetic heads are connected to a magnetic head controller, and the magnetic head controller is responsible for the movement of each magnetic head.
The physical structure of the hard disk
Hard disks store data based on the principle of electromagnetic conversion. The hard disk is composed of one or more metal or glass disks coated with magnetic materials on the surface. The magnetic head is installed on both sides of the disk and the corresponding control circuit. The disk and the head are sealed in a dust-free metal casing.
Mechanical hard disk physical structure and logical structure decomposition
When the hard disk is working, the disk rotates at a high speed at the design speed, and the magnetic head set on the surface of the disk moves radially to the designated position under the control of the circuit, and then stores or reads data. When the system writes data to the hard disk, the “write data” current in the magnetic head generates a magnetic field to change the state of the magnetic material on the surface of the disk, and after the write current magnetic field can still keep disappearing in order to store data; when the system comes from When reading data from a hard disk, the magnetic head passes through the designated area of the optical disc, and the magnetic field on the surface of the optical disc causes the magnetic head to generate an induced current or change in the impedance of the coil, and the data is restored after being processed by the relevant circuit.
Therefore, as long as the surface of the disk can be handled more smoothly, the head design is more precise, and the rotation speed of the disk is maximized, a hard disk with a larger capacity and faster read and write data speeds can be produced. This is because the surface of the disk is flatter and the rotation speed is faster, the closer the head is to the surface of the disk, and the read and write sensitivity and speed are higher. The smaller the head design, the more precisely the head can occupy space on the plate. , so that the head builds more tracks on the disk to store more data.
On March 22, 2018, Seagate demonstrated the world’s fastest mechanical hard drive at the Open Compute computing summit.
This redesigned HDD is actually based on a very simple principle, that is, “heavy work makes light work”, and introduces two drive arms (Mach.2 technology), each motor arm has 8 magnetic heads, and the upper Coaxial operation independently after power on.
Compared with the traditional single-motor 8-disk 16-head hard drive, the dual-motor arm means that twice as much data can be transmitted/retrieved, that is, the read and write performance is doubled (similar to Raid 0).
Taking the demonstration disk as an example, its continuous data transmission speed has reached 480MB/s, which is directly double the extreme value (235MB/s) of ordinary 7200 rpm and SATA3 hard disks.
At the same time, Seagate also showed another muscle, announcing that another key unit of HDD, the “disk surface” technology, HAMR (heat-assisted magnetic recording) has reached the industry standard.
HAMR is Seagate’s solution to increase storage density. It uses a special laser beam close to the Curie point temperature (138°C, the temperature at which magnetic materials permanently lose their magnetism) to heat the magnetic storage medium (over 400°C instantaneously), thereby reducing the write speed. The coercive force when entering data.
Seagate has manufactured a 20TB HAMR hard drive with a density of 2Tb per square inch (the current PMR/SMR does not exceed 1.5Tb).
In terms of reliability, the head life of HAMR hard drives has reached 6000 hours (equivalent to recording 3.2PB data), which is 20 times the current industry standard.
What’s even more powerful is that Seagate plans to introduce HAMR and Mach.2 technologies to the Exos enterprise product line at the same time, but the specific launch date is unknown. According to previous statements, the earliest is the second half of 2019.