Hard Disk Drives
Hard disk drive (HDD or HDD - Hard Disk Drive) is designed for long-term storage of data (operating system, user programs, created documents, etc.) required when working with a computer. It uses hard (aluminum) disks with a magnetic coating. One of the first HDD models includes drives containing two 30 MB disks. Their resultant capacity was designated like the caliber of a hunting rifle "Winchester" figures 30/30. Therefore, HDDs were called hard drives.
The subsystem of memory on the HDD includes:
• The drive itself;
• Controller, which is a device for controlling HDD in read/write modes;
• a multicore cable intended to connect the hard drive to the controller.
Features of the design of hard drives
The main design elements of hard drives are:
• a set of disks with a two-sided magnetic coating, which is the actual information store. Disks are made of a rigid material, located one under the other and fixed on the axis of rotation. The storage capacity of the hard drive is determined by the number of drive disks;
• The spindle motor is mechanically coupled to the axis on which the disks are fastened. The motor provides rotation of disks at a speed of 3600, 5400 or 7200 rpm;
• a magnetic read/write head unit. Each disc is served by a pair of magnetic heads. All heads are located crest & quot ;. Due to the air cushion formed during the rotation of the discs, the magnetic heads do not touch the surface of the discs. The distance between the disk and the head is 0.05-0.1 μm;
• A positioning device designed to simultaneously move all the block heads in the radial direction. As such a device, stepper motors or movable coils with a magnet are used. This positioning device allows you to select the desired cylinder, which is a collection of all tracks equidistant from the center of the discs;
• Filters. In the case of the hard drive there is a slot equipped with a microfilter for dust protection and designed to equalize the air pressure between the drive and the environment. Another filter serves to remove particles formed by the interaction of the mechanical parts of the disk;
• The mechanism of parking, designed to install the magnetic heads on the last cylinder and block their movement after turning off the power. Car parking eliminates possible damage to the head and the disc itself. When the computer starts, the heads are unlocked;
• a printed circuit board that contains electronic control circuits for the spindle motor and positioning device, nodes of the write/read paths, interface circuits, etc.
• the hard drive case, in which all the elements listed above are located.