Hard drive

A hard drive is an essential component of computer, be it a server model, a desktop model, or a laptop model. It is a permanent storage device with capacity of 10/ 20/ 40/ 60/ 80/ and 100 GB for desktops and laptops. A hard drive is also known as a hard disk drive (HDD), a hard disk, fixed disk, fixed drive, fixed disk drive, or a hard file. A hard drive is composed of magnetic surfaced hard disk platters on which data can be digitally encoded in a permanent fashion and is thus a non-volatile data storage device.

How data is stored and retrieved from a hard drive

The hard disk drive design is made up of a spindle holding one or more flat circular magnetic surfaced platters, made of non-magnetic material like glass or aluminium, that spin at a high speed on a high quality bearing. Previously, ball bearings were used, but nowadays, to reduce noise, friction, and heat, fluid bearings are used. As the platters rotate at high speed, read-write heads fly very close over the magnetic surface. The read-write head fly on air-bearing, a cushion of air that is nanometers above the disk surface. Due to the proximity of the highly localized and strong magnetic field of the read-write head, the magnetic medium on the disk surface changes its magnetization in microscopic spots. Thus, data writing is accomplished on the platter. For reading the data, a magnetoresistive (MR) read sensor is used which is also part of the same read-write head structure. As the head flies over the rotating disk, the read sensor picks up the magnetic flux emanating from the transitions passing underneath it via a small change of the MR sensor's electric resistance. This is converted by electronics into a stream so 1's and 0's. Latest hard disk technology employs self-monitoring, analysis, and reporting technology (S.M.A.R.T.) that can predict impending failures, thereby alerting the user of potential data loss. Due to spikes, surges, or other sudden voltage fluctuations, physical shocks, wear and tear, corrosion, or poorly manufactured disks and heads, if the nanometer gap between the read-write head and the disk is reduced, and the read-write head touches the high speed rotating disk platter, thereby scraping on the magnetic film and damaging the platter. This is known as a hard disk crash. In some instances, data recovery from the damaged platter is possible. Due to the submicroscopic gap between the platter and the read-write head, the internal environment of the hard disk has to remain immaculately clean from fingerprints, hair, dust, smoke particles, etc. Thus, the entire machinery of the hard disk is enclosed in a mostly sealed enclosure protecting from dust, condensation, hair, fingerprints, and other sources of contamination.

Hard disk technology designed for laptops

To improve stiction and wear performance, IBM around 1995, pioneered a technology known as Laser Zone Texture (LZT), by which an array of smooth nanometer-scale "bumps" were created in the ID landing zone by a precision laser process. Again, especially for laptops, IBM introduced the "heat unloading" technology. In this technology, the read-write heads were lifted off the platters onto plastic "ramps" near the outer disk edge, thereby the risk of stiction was eliminated altogether. The non-operating shock performance was also vastly improved. Advantages and drawbacks are there in these LZT and "heat unloading" technologies, in terms of cost of implementation, difficulty of mechanical tolerance control, and loss of storage space. However, as of now, all hard disk manufacturers use both these technologies. For their new "Thinkpad" line of laptops, IBM created an Active Protection System technology. This technology featured a built-in motion sensor in the Thinkpad, which could detect sudden and sharp movement. In such a case, the internal hard disk heads automatically unloaded themselves into the parking zone. This reduced the chances of scratches or potential data loss. Apple also used this same technology calling it as "Sudden Motion Sensor" technology and used it in their Powerbook and MacBook line of laptops. Notebook hard drives spin at 4,200 rpm or 5,400 rpm. The top models spin at 7,200 rpm offering the user almost desktop computer speed and performance. Used notebooks, cheap notebooks, and refurbished notebooks may have slower hard drives. New notebook computers, web cam notebooks, wireless notebooks, and tablet notebooks feature the latest hard drive technology.