Hard disk

Hard disk or hard disk (in English hard disk drive) is a storage device which, to store data or programs, uses a set of rotating discs with a magnetic coating, called platters. In everyday use, the terms hard disk, hard disk drive, and hard drive are interchangeable, because the disk and drive mechanism form the same entity. A typical hard disk platter rotates at speeds of up to 3600 rpm, and the read / write heads float on a 10 to 25 millionth inch thick air cushion, so they never come into contact with the recording surface. To prevent airborne pollutants from entering it and interfering with these tolerances,

Hard disks vary in capacity from a few tens of Megabytes to large amounts of Gigabytes of storage space. Also, the larger the disk, the more important is the strategy you use to make backups. Hard drives are trustworthy, yet they fail, usually at the most inopportune moment. These are a non-volatile device, which preserves information even with loss of energy, which uses a digital magnetic recording system. There are different standards to communicate a hard disk with the computer; the most common interfaces are Integrated Drive Electronics (IDE, also called ATA), SCSI generally used in servers, SATA, the latter standardized in 2004 and exclusive FC for servers.

As shipped from the factory, the hard drive cannot be used by an operating system. Before, a low-level format must be defined, one or more partitions and then we must give them a format that can be understood by our system.

There is also another type of disk called Solid State that uses a certain type of memory built with Semiconductors to store the information. The use of this class of disks was generally limited to Supercomputers, due to their high price, although much cheaper low-capacity drives (up to 512 GB) can now be found on the market for use in personal computers (above all portable). Thus, the Track Cache is a solid state memory, type RAM , inside a solid state hard disk.

Its translation from English is hard disk drive , but this term is rarely used, due to the practicality of the shorter term term hard disk (or hard disk ).


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  • 1 Physical structure
    • 1 Addressing
    • 2 Types of connection
    • 3 Form factor
  • 2 Logical structure
  • 3 Integrity
  • 4 Mechanical operation
  • 5 History
  • 6 Characteristics of a hard disk
  • 7 Present and future
  • 8 Manufacturers
  • 9 How to monitor the operation of the hard disk?
    • 1 Symptoms that the hard disk is damaged
    • 2 What to do when these symptoms appear?
    • 3 What program can be used to interpret SMART data?
  • 10 See also
    • 1 Leading manufacturers of hard drives
  • 11 External links

Physic structure

Inside a hard disk there are one or more plates (between 2 and 4 normally, although there are up to 6 or 7 plates), which are concentric (aluminum or glass) discs that rotate all at once. The head (read and write device) is a set of vertically aligned arms that move in or out as appropriate, all at the same time. At the tip of these arms are the read / write heads, which thanks to the movement of the head can read both interior and exterior areas of the disc.

Each platter has two faces , and a read / write head is required for each face (not one head per platter, but one per face). If you look at the Cylinder-Head-Sector scheme(below), at first glance you can see 4 arms, one for each plate. In reality, each of the arms is double, and contains 2 heads: one to read the upper face of the plate, and another to read the lower face. Therefore, there are 8 heads to read 4 plates, although for commercial reasons, not all the faces of the disks are always used and there are hard disks with an odd number of heads, or with disabled heads. The read / write heads never touch the disc, but pass very close (up to 3 Nanometers) or 3 millionths of a millimeter, due to a very thin film of air that forms between them and the plates when they rotate (some discs include a system that prevents the heads from passing over the plates until they reach a rotational speed that guarantees the formation of this film).


There are several concepts to refer to areas of the disk:

  • Plate: each of the disks inside the hard disk .
  • Face: each of the two sides of a
  • Head: number of heads.
  • Clue: a circumference within a face ; the track 0 is at the outer edge.
  • Cylinder: set of several tracks ; are all the circles that are vertically aligned (one on each side ).
  • Sector: each of the divisions of a track. The sector size is not fixed, the current standard being 512 bytes. In the past, the number of sectors per track was fixed, which wasted space significantly, since more sectors can be stored on the outer tracks than on the inside. Thus, the ZBR technology ( bit recording by zones ) appeared, which increases the number of sectors in the outer tracks, and uses the hard disk more efficiently.

The first addressing system used was the CHS ( cylinder-head-sector ), since with these three values ​​any data on the disk can be placed. Later, a simpler system was created: LBA ( logical block addressing ), which consists of dividing the entire disk into sectors and assigning each one a unique number. This is the one currently used.

Connection types

If we talk about a rigid disk we can mention the different types of connection that they have with the motherboard, that is, they can be SATA , IDE , SCSI or SAS .

  • IDE: Integrated Device Electronics (“Device with Integrated Electronics”) or ATA (Advanced Technology Attachment), controls mass data storage devices such as hard drives and ATAPI (Advanced Technology Attachment Packet Interface) Until recently, the main standard for its versatility and quality / price ratio.
  • SCSI: They are hard drives with a large storage capacity. They are presented under three specifications: Standard SCSI (Standard SCSI), Fast SCSI (Fast SCSI) and Wide-Fast SCSI (Fast-Wide SCSI). Its average access time can reach 7 msec and its sequential information transmission speed can theoretically reach 5 Mbps on Standard SCSI disks, 10 Mbps on Fast SCSI disks and 20 Mbps on Wide-Fast SCSI disks ( SCSI-2). A SCSI controller can handle up to 7 SCSI hard drives (or 7 SCSI peripherals) with a daisy-chain connection. Unlike IDE disks, they can work asynchronously relative to the microprocessor, making them faster.
  • SATASerial ATA ): New connection standard that uses a serial bus for data transmission. Noticeably faster and more efficient than IDE. There are currently two versions, SATA 1 up to 1.5 Gigabits per second (192 MB / s) and SATA 2 up to 3.0 Gb / s (384 MB / s) transfer speed.
  • SASSerial Attached SCSI): Serial data transfer interface, successor to parallel SCSI, although it still uses SCSI commands to interact with SAS devices. Increases speed and allows quick connection and disconnection. One of the main features is that it increases the transfer speed by increasing the number of connected devices, that is, it can manage a constant transfer rate for each connected device, in addition to ending the limitation of 16 existing devices in SCSI, it is by It is predicted that SAS technology will gradually replace its predecessor SCSI. In addition, the connector is the same as in the SATA interface and allows these hard drives to be used, for applications with less need for speed, saving costs. Thus,

Form factor

The earliest ” form factor ” of hard drives, it inherited its dimensions from floppy drives. They can be mounted on the same chassis and thus form factor hard drives were colloquially called FDD types ” floppy-disk drives “.

“Form factor” compatibility continues to be 3½ inches (8.89 cm) even after other types of floppy disks with smaller dimensions have been removed.

  • 8 inches:3 × 117.5 × 362 mm (9.5 × 4,624 × 14.25 inches).
    In 1979, Shugart Associatesreleased the first form factor compatible with hard drives, SA1000, having the same dimensions and being compatible with the 8-inch interface of the floppy drives. There were two versions available, the same height and the half (58.7mm).
  • 25 inches:146.1 × 41.4 × 203 mm (5.75 × 1.63 × 8 inches). This form factor is the first used by Seagate hard drives in 1980 with the same size and maximum height of 5¼-inch FDDs, for example: 82.5 mm maximum.
    This is twice as high as the 8-inch factor, which is commonly used today; for example: 41.4 mm (1.64 inches). Most 120mm optical drive ( DVD / CD ) models use the 5¼ half-height form factor size, but also for hard drives. The Quantum Bigfoot model is the last one used in the late 1990s.
  • 5 inches:101.6 × 25.4 × 146 mm (4 × 1 × 5.75 inches).
    This form factor is the first used by Rodine hard drives that are the same size as 3½, 41.4mm high drives. Today it has been largely replaced by the “slim” 25.4mm (1 inch) line, or “low-profile” that is used on most hard drives.
  • 5 inches:69.85 × 9.5-15 × 100 mm (2.75 × 0.374-0.59 × 3,945 inches).
    This form factor was introduced by PrairieTek in 1988 and does not correspond to the size of floppy drives. This is frequently used by the hard drives of mobile equipment (laptops, music players, etc …) and in 2008 it was replaced by 3.5-inch units of the multiplatform class. Today the dominance of this form factor is the 9.5mm notebook drives, but the larger capacity drives are 12.5mm tall.
  • 8 inches:54 × 8 × 71 mm.
    This form factor was introduced by Integral Peripherals in 1993 and was involved with ATA-7 LIF with the indicated dimensions and its use is increasing in digital audio players and its subnotebook. The original variant is 2GB to 5GB and fits in a PC expansion card slot . They are commonly used on iPods and MP3-based hard drives.
  • 1 inch:8 × 5 × 36.4 mm.
    This form factor was introduced in 1999 by IBMand Microdrive , suitable for compact flash type 2 slots, Samsung calls the same factor as 1.3 inches.
  • 85 inch:24 × 5 × 32 mm.
    Toshiba announced this form factor on January 8, 2004 for use in mobiles and similar applications, including SD / MMC slot compatible with 4G -optimized video and storage optimized for micro-mobiles . Toshiba currently sells 4GB (MK4001MTD) and 8GB (MK8003MTD) and 5GB versions hold the Guinness World Record for smallest hard drive.

Major manufacturers discontinued research on new products for 1-inch (1.3-inch) and 0.85-inch in 2007, due to falling flash memory prices , although Samsung introduced in 2008 with the SpidPoint A1 another unit of 1.3 inches.

The “inch” name for form factors does not normally identify any current products (they are specified in millimeters for the most recent form factors), but these indicate the relative size of the disk, for the sake of historical continuity.

Logical structure

Inside the disc are:

  • The Master Boot Record(in the Boot Sector ), which contains the Partition Table .
  • The partitions, necessary to be able to place the file systems .


Due to the extremely tight space between the heads and the disk surface, some contamination of the read / write heads or the sources can lead to an accident in the heads, a disk failure in which the head scratches the surface of the source, often grinding the thin magnetic film and causing data loss. These accidents can be caused by an electronic failure, a sudden cut in the electrical supply, physical shocks, wear and tear, Corrosion or due to poorly manufactured heads or sources.

The axis of the hard drive system depends on the air pressure inside the enclosure to support the heads and their correct height while the drive rotates. A hard drive requires a certain line of air pressures to function properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 0.5 mm in diameter) usually with a filter inside (breathing filter, see below). If the air pressure is too low, then there is not enough boost for the head, which is too close to the disk, and there is a risk of data failure and loss. Specially manufactured discs are necessary for high-altitude operations, over 3,000 m (10,000 ft). Please note that modern aircraft have a pressurized cabin whose pressure altitude does not normally exceed 2,600 m (8,500 ft). Therefore ordinary hard drives can be used safely on flights. Modern discs include temperature sensors and adjust to surrounding conditions. Vent holes can be seen on all discs (they usually have a sticker next to them warning the user not to cover the hole. The air inside the operating disc is in constant motion being swept away by friction from the platter. This air passes through an internal recirculation filter to remove any contaminant that may have remained from its manufacture, any particle or chemical component that had somehow entered the premises, and any particles generated in normal operation. Very high humidity over a long period can corrode the heads and plates.

For large magnetism resistant (GMR) heads in particular, a minor incident due to contamination (which does not dissipate the magnetic surface of the disc) results in temporary overheating of the head due to surface friction of the disk, and may render the data unreadable for a short period of time until the head temperature stabilizes (also known as “thermal roughness”, a problem that can be partly treated with the appropriate electronic filter of the read signal).

The electronic components of the hard drive control the movement of the actuator and the rotation of the disk, and perform reads and writes required by the disk controller. The firmware of modern drives is capable of scheduling reads and writes efficiently on the surface of the disks and reallocate sectors that have failed.

Mechanical operation

A hard drive usually has:

  • Dishes where the data is recorded.
  • Read / write head.
  • Engine that turns the plates.
  • Electromagnet that moves the head.
  • Electronic control circuit, which includes: interface with the computer, cache memory.
  • Desiccant sachet (Silica gel) to avoid humidity.
  • Box, which must protect from dirt, which is why it usually has an air filter. Hard drives are not vacuum sealed in their cases as is often thought; in fact, many discs have a mechanical system that does not allow the heads to come out to the surface of the plates if they do not have an adequate speed of rotation, and this system consists of a flange that is pushed by the air inside the box of the disc when it moves at sufficient speed. When the tab is pushed, the heads are unlocked.
  • Screws, often Torx type.


In the beginning, hard drives were removable, however, today typically they all come sealed (except for a ventilation hole to filter and equalize air pressure).

The first hard drive, released in 1956 , was the IBM 350 Model 1, presented with the Ramac I computer : it weighed a ton and its capacity was 5 MB. Larger than a current fridge, this hard drive still operated with vacuum valves and required a separate console for handling.

Its great merit consisted in the fact that the time required for access was relatively constant between some memory locations, unlike magnetic tapes, where in order to find a given information, it was necessary to reel and unwind the reels until finding the desired data, having very different access times for each position.

The initial technology applied to hard drives was relatively simple. It consisted of covering a metal disk with magnetic material that was formatted in concentric tracks, which were then divided into sectors. The magnetic head encoded information by magnetizing tiny sections of the hard drive, using a binary code of “zeros” and “ones.” The bits or binary digits recorded in this way can remain intact for years. Originally, each bit had a horizontal arrangement on the magnetic surface of the disk, but then it was discovered how to record information in a more compact way.

The merit of the French Albert Fert and the German Peter Grünberg (both Nobel Prize in Physics , for their contributions in the field of magnetic storage) was the discovery of the phenomenon known as giant magnetoresistance, allowed to build more sensitive reading and recording heads, and compact plus bits on the surface of the hard drive. These discoveries, made independently by these researchers, led to a dramatic growth in storage capacity on hard drives, which rose 60% annually in the 1990s.

In 1992, 3.5-inch hard drives housed 250 MB, while 10 years later they had exceeded 40,960 MB or 40 gigabytes (GB). Today, we already have hard drives of more than one terabyte (TB) or 1,048,576 megabytes in everyday use.

In 2005 the first mobile phones that included hard drives were introduced by Samsung and Nokia.

Characteristics of a hard disk

The characteristics that must be taken into account in a hard disk are:

  • Average accesstime: Average time it takes for the needle to get to the track and the desired sector; it is the sum of the average Search time (being on the track), reading / writing time and the average Latency (being in the sector).
  • Average searchtime: Average time it takes for the needle to get to the desired track; it is half the time spent by the needle going from the most peripheral to the most central track of the disc.
  • Read / writetime: Average time it takes for the disc to read or write new information, the time depends on the amount of information you want to read or write, the block size, the number of spindles, the time per lap and the number of sectors per track.
  • Average latencyAverage time it takes for the needle to be in the desired sector; it is half the time spent in a complete rotation of the disk.
  • Rotation speed: Revolutions per minute of the plates. The higher the rotation speed, the lower average latency.
  • Transfer Rate: The rate at which you can transfer the information to the computer once the needle is on the correct track and sector. It can be sustained or peak speed .

Other features are:

  • Track cache: It is a RAM memory inside the hard disk. Solid state hard drives use certain types of memory built with Semiconductors to store information. The use of this class of disks is generally limited to Supercomputers, due to their high price.
  • Interface: Communication medium between the hard disk and the computer. Can be IDE / ATA , SCSI , SATA , USB , Firewire , SAS
  • Landz: Area where heads land once the computer is turned off.

Present and future

Currently the new generation of hard drives use Perpendicular Recording (PMR) technology, which allows for higher storage density. There are also discs called “Ecological” (GP – Green Power), which make more efficient use of energy. It is beginning to be observed that the Solid State Drive may end up replacing the hard drive in the long term. We must also add the new hard drives based on the type of Flash memory, which some companies, such as ASUS, recently incorporated in their models. They start at 4GB to 512GB.

They are very fast since they have no moving parts and consume less energy. All of this makes them very reliable and almost indestructible. A new format of hard drives based on memory cards. However, its cost per GB is still very high since the cost of a common 500 GB hard drive is equivalent to an 8 to 16 GB SSD, approximately $ 50 USD.


The technological resources and know-how required for the development and production of modern drives means that since 2007, more than 98% of the world’s hard drives have been manufactured by a group of large companies: Seagate (which now owns Maxtor ) , Western Digital , Samsung and Hitachi (which owns IBM’s former record manufacturing division ). Fujitsu continues to make portable disks and server disks, but stopped making disks for desktop computers in 2001, with the rest sold to Western Digital. Toshibais one of the leading manufacturers of 2.5-inch and 1.8-inch laptop hard drives. ExcelStor is a small manufacturer of hard drives.

Dozens of former hard drive manufacturers have either terminated their merged companies or closed their hard drive divisions, as device capacity and product demand increased, profits were lower, and the market underwent significant consolidation. in the late 1980s and late 1990s. The first victim in the PC market was Computer Memories Inc. or CMI; After an incident with a 20MB flaw in disks in 1985, CMI’s reputation never recovered, and they went out of the hard drive market in 1987. Another notable failure was MiniScribe , who went bust in 1990 after it was discovered that they were running. fraud and inflated the number of sales for several years. Many other small companies (such as Kalok, Microscience , LaPine, Areal, Priam and PrairieTek) also did not survive the expulsion, and had disappeared by 1993; Micropolis was able to hold out until 1997, and JTS , a newcomer to the scene, lasted only a few years and disappeared in 1999, then tried to make hard drives in India. His return to fame was with the creation of a new 3 ”notebook format. Quantum and Integral also investigated the 3 ”format, but ultimately gave up. RodimeHe was also a major manufacturer during the 1980s, but stopped making records in the 1990s in the midst of restructuring and is now concentrating on licensing technology; They have several patents related to the 3.5 “format.

  • 1988: Tandon Corporationsold its hard drive manufacturing division to Western Digital (WDC), which was a renowned driver designer.
  • 1989: Seagate Technologybought Control Data’s high-quality disk business as part of CDC’s abandonment of hardware creation.
  • 1990: Maxtor bought MiniScribethat was bankrupt, making it the core of its low-end disc division.
  • 1994: Quantumpurchased the [Digital Equipment Corporation | DEC] storage division giving the user a range of high-quality drives called ProDrive, just like DLT’s tape drive range
  • 1995: Conner Peripheralswas founded by one of Seagate Technology’s co-founders along with MiniScribe staff, they announced a merger with Seagate, which was completed in early 1996.
  • 1996: JTS merged with Atari, allowing JTS to bring their range of records to production. Atari was sold to Hasbro in 1998, while JTS went bankrupt in 1999.
  • 2000: Quantum sold its disk division to Maxtor to focus on tape drives and backup equipment.
  • 2003: Following the controversy over massive failures in its Deskstar 75GXPmodel , pioneer IBM sold most of its disk division to Hitachi, renaming it Hitachi Global Storage Technologies (HGST).
  • 2003: Western Digital bought Read-Rite Corp, which produced the heads used in hard drives, for $ 95.4 million in cash.
    • December 21, 2005: Seagateand Maxtor announce an agreement under which Seagate would acquire all of Maxtor’s stock for $ 90 billion. This acquisition was approved by regulatory bodies, and closed on May 19, 2006.
  • 2007
    • July: Western Digital (WDC) acquires Komag USA, a manufacturer of the material that covers the plates of the hard disks, for one hundred ninety billion dollars.

How to monitor the performance of the hard disk?

The fact is that all hard drives are going to fail, it may take a month or years but there will come a time when it will not work anymore and this is when it is most important to make a backup to prevent the data you have from being lost. In some cases there will be signs that the hard drive is about to be damaged, but in others it will be somewhat surprising.

Symptoms that the hard disk is damaged

If you do not have software that detects defects, there are some symptoms that could indicate that the hard disk is about to be damaged. This will not say how long it will stop working and in some cases these signs will not even appear. However, you should be aware of these.

  • It hangs or crashes frequently and irregularly, especially when the Operating System is starting
  • Cryptic, strange and frequent errors appear when doing normal things, like copying a file from one side to another.
  • File and folder names that have been completely changed without permission.
  • Files disappear.
  • You are waiting too long to enter to visit a folder or to open a file.
  • Unreadable files when files are opened or sent to print.
  • Heavy-duty sounds are heard on the hard drive.

This last symptom is very important because it is usually a striking indicator, especially since modern hard drives are usually quieter. If you hear that something has changed in the sound you make while working, then there may be a problem.

What to do when these symptoms appear?

If any of these symptoms appear, it is ideal to check the hard drive right away to make sure there is a problem. This can be done quickly with some specialized software . An advantage is that modern hard drives use something called SMART , which stands for “Self Monitoring Analysis and Reporting Technology” and that will help detect and show malfunctions. There are applications that read SMART data and translate it to be understood by anyone. Once the problem is reported or if one exists, then it is recommended to immediately back up to an external disk. This practice should always be done as a precautionary measure.

What program can be used to interpret SMART data?

There are many applications that allow an analysis of the hard disk to discover what problems it has; for example, HDDscan. Another recommended is HDDExpert , a completely free application that will check the disk whether it is an HDD or an SSD to find out how it is working and your health in general. The best that this program offers is the translation of all SMART information to know exactly what is happening, and also suggests maintenance operations that will depend on the results obtained.


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