HARD DISK DRIVE

A storage device may hold information, process information, or both. A device that only holds information is a recording medium. Devices that process information (data storage equipment) may either access a separate portable (removable) recording medium or a permanent component to store and retrieve information.

Electronic data storage is storage which requires electrical power to store and retrieve that data. Most storage devices that do not require vision and a brain to read data fall into this category. Electromagnetic data may be stored in either an analog or digital format on a variety of media. This type of data is considered to be electronically encoded data, whether or not it is electronically stored in a semiconductor device, for it is certain that a semiconductor device was used to record it on its medium. Most electronically processed data storage media (including some forms of computer data storage) are considered permanent (non-volatile) storage, that is, the data will remain stored when power is removed from the device. In contrast, most electronically stored information within most types of semiconductor (computer chips) microcircuits are volatile memory, for it vanishes if power is removed.

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.

HDDs (introduced in 1956 as data storage for an IBM accounting computer) were originally developed for use with general purpose computers. In the 21st century, applications for HDDs have expanded to include digital video recorders, digital audio players, personal digital assistants, digital cameras and video game consoles. In 2005 the first mobile phones to include HDDs were introduced by Samsung and Nokia.The need for large-scale, reliable storage, independent of a particular device, led to the introduction of embedded systems such as RAID arrays, network attached storage (NAS) systems and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data.

The commercial usage of hard disk drives began in 1956 with the shipment of an IBM 305 RAMAC system including IBM Model 350 disk storage.

In the early 1960s single data bits were stored as magnetic charges in a magnetic core memory.

Then the scientists at IBM in San Jose, California created a rotating drum that was coated in a magnetically polarizable film that could be used to store data by changing and sensing magnetic polarization. The drum was later superseded by disks, because of their lower mass and inertia. Rey Johnson, an inventor who worked for IBM for many years, is said to be the "father" of the disk drive.

The random-access, low-density storage of disks was developed to complement the already used sequential-access high-density storage provided by magnetic tape. Vigorous innovation in disk storage technology, coupled with less vigorous innovation in tape storage, has reduced the density and cost per bit gap between disk and tape, reducing the importance of tape as a complement to disk.

In the beginning, there were movable head devices, usually disks, and fixed head devices, usually drums. Movable head devices store more data per magnetic sensor and usually more per area of the medium. Fixed head devices avoid the seek time, while the head moves to the data. Fixed head devices have not been common since integrated circuit random access memory was developed. So the usual storage devices of, for example, an IBM 360 were discrete transistor registers, magnetic core random access memory (ram), fixed head drums, movable head disk packs (several disks with the heads connected mechanically), and magnetic tape, in order of increasing time to access a random data element.

For many years, hard disk drives were large, cumbersome devices, more suited to use in the protected environment of a data center or large office than in a harsh industrial environment (due to their delicacy), or small office or home (due to their size and power consumption). Before the early 1980s, most hard disk drives had 8-inch (actually, 210 - 195 mm) or 14-inch platters, required an equipment rack or a large amount of floor space (especially the large removable-media drives, which were frequently comparable in size to washing machines), and in many cases needed high-current and/or three-phase power hookups due to the large motors they used. Because of this, hard disk drives were not commonly used with microcomputers until after 1980, when Seagate Technology introduced the ST-506, the first 5.25-inch hard drives, with a formatted capacity of 5 megabytes.

The capacity of hard drives has grown exponentially over time. With early personal computers, a drive with a 20 megabyte capacity was considered large. During the mid to late 1990s, when PCs were capable of storing not just text files and documents but pictures, music, and video, internal drives were made with 8 to 20 GB capacities. As of mid 2008, desktop hard disk drives typically have a capacity of 500 to 750 gigabytes, while the largest-capacity drives are 1.5 terabytes.

An eco-friendly drive from Fabrik built with bamboo and recyclable aluminum.

An external hard disk drive is a type of hard disk drive which is externally connected to a computer. Modern entries into the market consist of standard SATA, IDE, or SCSI hard drives in portable disk enclosures with SCSI, USB, IEEE 1394 Firewire, eSATA client interfaces to connect to the host computer.

The first commercial hard disks were large and cumbersome, were not stored within the computer itself, and therefore fit within the definition of an external hard disk. The hard disk platters were stored within protective covers or memory units, which sit outside. These hard disks soon evolved to be compact enough that the disks were able to be mounted into bays inside a computer. Early Apple Macintosh computers did not have easily accessible hard drive bays (or, in the case of the Mac Plus, any hard drive bay at all), so on those models, external SCSI disks such as the Apple ProFile were the only reasonable option. Early external drives were not as compact or portable as their modern descendents.

By the end of the 20th century, internal drives became the system of choice for computers running Windows, while external hard drives remained popular for much longer on the Apple Macintosh and other professional workstations which offered external SCSI ports. Apple made such interfaces available by default from 1986 and 1998. The addition of USB and Firewire interfaces to standard personal computers led such drives to become commonplace in the PC market as well. These new interfaces supplanted the more complex and expensive SCSI interfaces, leading to standardization and cost reductions for external hard drives.

Modern external hard drives are compatible with all operating systems supporting the relevant interface standards they operate with, such as USB MSC or IEEE1394. These standards are supported by all major modern server and desktop operating systems and many embedded devices. Obsolete systems such as Windows 98^[7] and bundled backup and encryption software may require the installation of additional software. The drives are partitioned and formatted in the same manner as internal hard disk drives: Given the lack of any universally supported filesystem (barring the obsolete FAT file system family), owners often need to reformat these drives upon purchase to achieve full compatibility with operating systems such as Mac OS X and Linux.

A hybrid drive or Hybrid Hard Drive (HHD) is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it uses a smaller solid-state drive (SSD) as a cache. The cache typically uses non-volatile flash memory, but some drives use battery backed RAM (a Hybrid RAM disk). The flash memory buffer can speed up repeated reads; a RAM buffer speeds both reads and writes, but must be written to backup storage when power is lost. Samsung claims that a flash based hybrid offers numerous benefits, chief among them speed of data access and consequent faster computer boot process, decreased power consumption, and improved reliability.

Samsung released the first hybrid drives, primarily for notebook computers, to OEMs in March 2007.

As of early 2008 the special features of hybrid drives are only taken advantage of by Microsoft's Windows Vista: the operating system files required for booting are stored in the fast flash memory, reducing boot time by about 11%.Microsoft uses the name Ready Drive to describe the software side of this technology.While hybrid drives are not required for Vista Premium certification of laptops, some confusion arose as to whether such drives would be mandatory.

The hybrid drive command interface will be standardized in the new revision 8 of the ATA standard.

A hybrid drive may be created from separate devices, managed by software, such as Ready Boost.

Hybrid Hard Disk Drives combine a magnetic hard disk drive and flash memory into a single device. Here, the high density of magnetic hard disk drive and low power, high reliability and high speed of flash memory technology come together. In a hybrid hard disk drive, non- volatile cache is used to store frequently accessed sectors and critical system data. Those portions of operating systems required during booting are stored in flash memory, thus speeding up booting process. Most of the time disk spindle is kept idle, thus saving power. NAND flash memory is incorporated in a hybrid hard disk using NAND design options such as the use of embedded flash disk. Hybrid hard disks have several benefits such as hard disk power consumption is reduced by about 70-90%, faster boot and resume from hibernation. They are more rugged and shock resistant. Hybrid hard disk drives are expected to be available in market toward the end of 2006 and in mainstream situation by 2007-2008.

PC hard disk drive capacity (in GB). The vertical axis is logarithmic, so the fit line corresponds to exponential growth.

Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive. Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit it faster. As of January 2008:

• A typical desktop HDD might store between 120 GB and 1 TB of data (based on US market data), rotate at 5,400 to 10,000 rpm and have a media transfer rate of 1 Gbit/s or higher. (1 GB = 10⁹ B; 1 Gbit/s = 10⁹ bit/s)
• As of July 2008^[update], the highest capacity HDDs are 1.5 TB.
• The fastest “enterprise” HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s. and a sustained transfer rate up to 125 MBytes/second. Drives running at 10,000 or 15,000 rpm use smaller platters because of air drag and therefore generally have lower capacity than the highest capacity desktop drives.
• Mobile, i.e., laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have less capacity. A typical mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a slight price premium. Because of the smaller disks, mobile HDDs generally have lower capacity than the highest capacity desktop drives.