USB flash drive,HDD and SSD
USB flash drive,HDD and SSD
A USB flash drive is a data storage device that includes flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than an optical disc. Most weigh less than 30 grams (1.1 oz).[ Sony SVS13AA11L Battery
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1] As of September 2011, drives of up to 256 gigabytes (GB) are available.[2] A one-terabyte (TB) drive was unveiled at the 2013 Consumer Electronics Show and will be available during 2013.[3] Storage capacities as large as 2 TB are planned, with steady improvements in size and price per capacity expectedSony SVS131A11L Battery
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.[4] Some allow up to 100,000 write/erase cycles, depending on the exact type of memory chip used, and a 10-year shelf storage time.[5][6][7] Sony SVS131B11L Battery
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USB flash drives are often used for the same purposes for which floppy disks or CD-ROMs were used, i.e., for storage, back-up and transfer of computer files. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because they have no moving parts. Until about 2005, most desktop and Sony PCG-41411L Batterylaptop computers were supplied with floppy disk drives in addition to USB ports, but floppy disk drives have been abandoned due to their lower capacity compared to USB flash drives. Sony SVS151A11L Battery
USB flash drives use the USB mass storage standard, supported natively by modern operating systems such as Linux, Mac OS X, Windows, and other Unix-like systems, Sony SVS151B11L Battery
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as well as many BIOS boot ROMs. USB drives with USB 2.0 support can store more data and transfer faster than much larger optical disc drives like CD-RW or DVD-RW drives and can be read by many other systems such as the Xbox 360, PlayStation 3, DVD players and in a number of handheld devices such as smartphones and tablet computers. Sony PCG-4121DL Battery
A flash drive has no moving parts to be driven; therefore, it's not a true drive. The term drive persists because computers read and write flash drive data using the same system commands as for a mechanical disk drive, with the storage appearing to the computer operating system and user interface as just another drive. Sony PCG-4121EL Battery
A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case which can be carried in a pocket or on a key chain, for example. Sony PCG-4121FL Battery
The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. Most flash drives use a standard type-A USB connection allowing connection with a port on a personal computer, but drives for other interfaces also exist. Sony PCG-4121GL Battery
USB flash drives draw power from the computer via the USB connection. Some devices combine the functionality of a digital audio player with USB flash storage; they require a battery only when used to play music. Leader providers are Gartner and Kingston Technology. Sony PCG-41211L Battery
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USB flash drives were invented by Amir Ban, Dov Moran and Oron Ogdan, all of the Israeli company M-Systems, who filed US patent 6,148,354 in April 1999;[8] however, the patent describes a product that has a cable between the memory unit and the USB connector. Sony PCG-41212L Battery
Sony PCG-41217L Battery [citation needed] IBM Patent Disclosure RPS8-1999-0201 from September 13, 1999 by Shimon Shmueli accurately describes the USB flash drive.[citation needed] IBM partnered with M-Systems to bring the product to market. Shmueli was later an expert witness for M-Systems and as part of his testimony in the Singapore court presented the IBM disclosure and evidence to the fact that he invented the USB flash
Sony PCG-41216L Batterydrive.[citation needed] M-Systems' product, developed by a team led by Dan Harkabi, and named the DiskOnKey, was announced in September 2000.[9] Competing claims have been made by a Singaporean company Trek Technology and a Chinese company Netac Technology,[10] but based on patents that post-date M-Systems'.
Sony PCG-41215L Battery Both Trek Technology and Netac Technology have tried to protect their patent claims. Trek won a Singaporean suit,[11] but a court in the United Kingdom revoked one of Trek's UK patents.[12] While Netac Technology has brought lawsuits against PNY Technologies,[1Sony PCG-41213L Battery
Sony PCG-41214L Battery3] Lenovo,[14] aigo,[15] Sony,[16][17][18] and Taiwan's Acer and Tai Guen Enterprise Co,[18] most companies that manufacture USB flash drives do so without regard for Trek and Netac's patents.
Pua Khein-Seng from Malaysia claims to have incorporated the world's first single chip USB flash controller. He is currently the CEO of Phison Electronics Corp, which is based in Taiwan.[19] sony PCG-4R2L battery
First commercial product[edit source | editbeta]
Trek Technology and IBM began selling the first USB flash drives commercially in 2000. Trek Technology sold a model under the brand name "ThumbDrive", and IBM marketed the first such drives in North America with its product named the "DiskOnKey," which was developed and manufactured by M-Systems.[20] IBM's USB flash drive became available on December 15, 2000,[ sony PCG-4R1L battery
21] and had a storage capacity of 8 MB, more than five times the capacity of the then-common floppy disks.
In 2000, Lexar introduced a Compact Flash (CF) card with a USB connection, and a companion card read/writer and USB cable that eliminated the need for a USB hub.[citation needed] sony PCG-4Q4L battery
Second generation[edit source | editbeta]
This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2011) sony PCG-4Q1L battery
Modern flash drives have USB 2.0 connectivity. However, they do not currently use the full 480 Megabit per second (Mbit/s) (60 Megabytes per second (MB/s)) which the USB 2.0 Hi-Speed specification supports because of technical limitations inherent in NAND flash and the overhead required for USB data transfers (8-bit / 10-bit sony PCG-6X1L battery
encoding and protocol). The fastest drives currently available use a dual channel controller, although they still fall considerably short of the transfer rate possible from a current generation hard disk, or the maximum high speed USB throughput.
File transfer speeds vary considerably. Speeds may be given in megabytes (Mbyte) per second, Megabits per second (Mbit/s) or optical drive multipliers such as "180X" (180 times 150 Kibibyte(KiB) per second). Typical fast drives claim to read at up to 30 megabytes/s (MB/s) and write at about half that speed. sony PCG-6X2L battery
sony PCG-6Z1L batteryThis is about 20 times faster than USB 1.1 "full speed" devices, which are limited to a maximum speed of 12 MB/s (1 MB/s with overhead).
Third generation[edit source | editbeta]
This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2011) sony PCG-6X6L battery
Like USB 2.0 before it, USB 3.0 offers dramatically improved data transfer rates compared to its predecessor. USB 3.0 was announced in late 2008, but consumer devices were not available until the beginning of 2010. The USB 3.0 interface specifies transfer rates up to 5 Gbit/s (625 MB/s), sony PCG-6X8L battery
compared to USB 2.0's 480 Mbit/s (60 MB/s). All USB 3.0 devices are backward compatible with USB 2.0 ports. Computers with USB 3.0 ports are becoming very popular and common. Many newer laptops and desktops have at least one such port. USB 3.0 port expansion cards are available to upgrade older systems, sony PCG-6XAL battery
sony PCG-6XBL batteryand many newer motherboards feature two or more USB 3.0 jacks. Even though the USB 3.0 interface allows extremely high data transfer speeds, as of 2011 most USB 3.0 flash drives do not utilize the full speed of the USB 3.0 interface due to limitations of their memory controllers (though some four channel memory controllers are now coming to market). Sony PCG-61A11L Battery
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Design and implementation[edit source | editbeta]
On a USB flash drive, one end is fitted with a single Standard-A USB plug. Inside the plastic casing is a small printed circuit board, which has some power circuitry and a small number of surface-mounted integrated circuits (ICs). Typically, one of these ICs provides an interface between the USB connector and the onboard memory, while the other is the flash memory. Sony PCG-61A13L Battery
Flash memory combines a number of older technologies, with lower cost, lower power consumption and small size made possible by advances in microprocessor technology. Sony PCG-61A14L Battery
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The memory storage was based on earlier EPROM and EEPROM technologies. These had limited capacity, were slow for both reading and writing, required complex high-voltage drive circuitry, and could only be re-written after erasing the entire contents of the chip. Sony PCG-71C11L Battery
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Hardware designers later developed EEPROMs with the erasure region broken up into smaller "fields" that could be erased individually without affecting the others. Altering the contents of a particular memory location involved copying the entire field into an off-chip buffer memory, erasing the field, Sony PCG-71C12L Battery
Sony PCG-71913L Batterymodifying the data as required in the buffer, and re-writing it into the same field. This required considerable computer support, and PC-based EEPROM flash memory systems often carried their own dedicated microprocessor system. Flash drives are more or less a miniaturized version of this. Sony PCG-61714L Battery
The development of high-speed serial data interfaces such as USB made semiconductor memory systems with serially accessed storage viable, and the simultaneous development of small, high-speed, low-power Sony PCG-61813L Battery
Sony PCG-71912L Batterymicroprocessor systems allowed this to be incorporated into extremely compact systems. Serial access requires far fewer electrical connections for the memory chips than does parallel access, which has simplified the manufacture of multi-gigabyte drives. Sony PCG-61911L Battery
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Computers access modern flash memory systems very much like hard disk drives, where the controller system has full control over where information is actually stored. The actual EEPROM writing and erasure processes are, however, still very similar to the earlier systems described above. Sony PCG-61913L Battery
Many low-cost MP3 players simply add extra software and a battery to a standard flash memory control microprocessor so it can also serve as a music playback decoder. Most of these players can also be used as a conventional flash drive, for storing files of any type. Sony PCG-71614L Battery
Some manufacturers differentiate their products by using elaborate housings, which are often bulky and make the drive difficult to connect to the USB port. Because the USB port connectors on a computer housing are often closely spaced, Sony PCG-71713L Battery
Sony PCG-71811L Batteryplugging a flash drive into a USB port may block an adjacent port. Such devices may only carry the USB logo if sold with a separate extension cable. Such cables are USB-compatible but do not conform to the USB standard.[24][25] Sony PCG-61713L Battery
USB flash drives have been integrated into other commonly carried items, such as watches, pens, and even the Swiss Army Knife; others have been fitted with novelty cases such as toy cars or LEGO bricks. Particularly in the Far East bizarre USB flash drives with images of dragons, cats or aliens are very popular.[2Sony PCG-91111L Battery
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6] The small size, robustness and cheapness of USB flash drives make them an increasingly popular peripheral for case modding.
File system[edit source | editbeta]
Main article: Flash file system
Most flash drives ship preformatted with the FAT12, FAT16. FAT32, or ExFat file systems. The ubiquity of this file system allows the drive to be accessed on virtually any host device with USB support. Also, standard FAT Sony PCG-91112L Battery
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maintenance utilities (e.g., ScanDisk) can be used to repair or retrieve corrupted data. However, because a flash drive appears as a USB-connected hard drive to the host system, the drive can be reformatted to any file system supported by the host operating system. Sony PCG-71312L Battery
Defragmenting: Flash drives can be defragmented. There is a widespread opinion that defragmenting brings little advantage (as there is no mechanical head that moves from fragment to fragment), and that defragmenting shortens the life of the drive by making many unnecessary writes.[2Sony PCG-71311L Battery
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7] However some sources claim[28] that defragmenting a flash drive can improve performance (mostly due to improved caching of the clustered data), and the additional wear on flash drives may not be significant.
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Even Distribution: Some file systems are designed to distribute usage over an entire memory device without concentrating usage on any part (e.g., for a directory) to prolong the life of simple flash memory devices. Some USB flash drives have this 'wear leveling' feature built into the software controller to prolong device life, while others do not, so it is not necessarily helpful to install one of these file systems.[29] Sony PCG-71218L Battery
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Hard Drive: Sectors are 512 bytes long, for compatibility with hard drives, and the first sector can contain a master boot record and a partition table. Therefore, USB flash units can be partitioned just like hard drives.
Longevity[edit source | editbeta] Sony PCG-71313L Battery
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The memory in flash drives is commonly engineered with multi-level cell (MLC) based memory that is good for around 3,000-5,000 program-erase cycles,[30] but some flash drives have single-level cell (SLC) based memory that is good for around 100,000 writes. Sony PCG-71315L Battery
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There is virtually no limit to the number of reads from such flash memory, so a well-worn USB drive may be write-protected to help ensure the life of individual cells.
Regardless of the endurance of the memory itself, the USB connector hardware is specified to withstand only around 1,500 insert-removal cycles.[31] Sony PCG-71316L Battery
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Fake products[edit source | editbeta]
Fake USB flash drives are sometimes sold, claiming to have higher capacities than they actually have. These are typically low capacity USB drives which are modified so that they emulate larger capacity drives (e.g., a 2 GB drive being marketed as an 8 GB drive). When plugged into a computer, Sony PCG-71317L Battery
they report themselves as being the larger capacity they were sold as, but when data is written to them, either the write fails, the drive freezes up, or it overwrites existing data. Software tools exist to check and detect fake USB drives.[32][33] In some cases it is possible to repair these devices to remove the false capacity information and use them normally. [34] [3Sony PCG-71318L Battery
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Sony PCG-71212L Battery5]
File transfer speeds[edit source | editbeta]
USB flash drives usually specify their read and write speeds in megabytes per second (MB/s); read speed is usually faster. These speeds are for optimal conditions; real-world speeds are usually slower. In particular, circumstances that often lead to speeds much lower than advertised are transfer (particularly writing) of many small files rather than a few very large ones, and mixed reading and writing to the same device. Sony PCG-71215L Battery
Sony PCG-71216L BatteryIn a typical well-conducted review[36] of a number of high-performance USB 3.0 drives, a drive that could read large files at 68MB/s and write at 46MB/s, could only manage 14MB/s and 0.3MB/s with many small files. When combining streaming reads and writes the speed of another drive, that could read at Sony PCG-61412L Battery
92MB/s and read at 70MB/s, was 8MB/s. These differences differ radically from one drive to another; some drives could write small files at over 10% of the speed for large ones. The examples given are chosen to illustrate extremes.
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Uses[edit source | editbeta]
Personal data transport[edit source | editbeta]
The most common use of flash drives is to transport and store personal files, such as documents, pictures and videos. Individuals also store medical information on flash drives for emergencies and disaster preparation.
Secure storage of data, application and software files[edit source | editbeta] Sony PCG-71111L Battery
With wide deployment(s) of flash drives being used in various environments (secured or otherwise), the issue of data and information security remains important. The use of biometrics and encryption is becoming the norm with the need for increased security for data; on-the-fly encryption systems are particularly useful in this regard, as they can transparently encrypt large amounts of data. In some cases a secure USB drive may use a
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hardware-based encryption mechanism that uses a hardware module instead of software for strongly encrypting data. IEEE 1667 is an attempt to create a generic authentication platform for USB drives. It is supported in Windows 7 and Windows Vista (Service Pack 2 with a hotfix).[37] Sony PCG-81111L Battery
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Application carriers[edit source | editbeta]
Flash drives are used to carry applications that run on the host computer without requiring installation. While any standalone application can in principle be used this way, many programs store data, configuration information, etc. on the hard drive and registry of the host computer. Sony PCG-81112L Battery
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The U3 company works with drive makers (parent company SanDisk as well as others) to deliver custom versions of applications designed for Microsoft Windows from a special flash drive; Sony PCG-81113L Battery
Sony PCG-81311L BatteryU3-compatible devices are designed to autoload a menu when plugged into a computer running Windows. Applications must be modified for the U3 platform not to leave any data on the host machine. U3 also provides a software framework for independent software vendors interested in their platform. Sony PCG-81114L Battery
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Ceedo is an alternative product, with the key difference that it does not require Windows applications to be modified in order for them to be carried and run on the drive.
Similarly, other application virtualization solutions and portable application creators, such as VMware ThinApp (for Windows) or RUNZ (for Linux) can be used to run software from a flash drive without installation. Sony PCG-6Z2M battery
In October 2010, Apple Inc. released their newest iteration of the MacBook Air, which had the system's restore files contained on a USB card drive rather than the traditional install CDs, due to the Air not coming with an optical drive.[38] Sony PCG-6X4M battery
A wide range of portable applications which are all free of charge, and able to run off a computer running Windows without storing anything on the host computer's drives or registry, can be found in the list of portable software.
Computer forensics and law enforcement[edit source | editbeta]
A recent development for the use of a USB Flash Drive as an application carrier is to carry the Computer Online Forensic Evidence Extractor (COFEE) application developed by Microsoft. COFEE is a set of applications designed to search for and extract digital evidence on computers confiscated from suspects.[39 Sony PCG-91311M battery
] Forensic software is required not to alter, in any way, the information stored on the computer being examined. Other forensic suites run from CD-ROM or DVD-ROM, but cannot store data on the media they are run from (although they can write to other attached devices, such as external drives or memory sticks). Sony PCG-71316M battery
Booting operating systems[edit source | editbeta]
Most current PC firmware permits booting from a USB drive, allowing the launch of an operating system from a bootable flash drive. Such a configuration is known as a Live USB. Sony PCG-71318M battery
Original flash memory designs had very limited estimated lifetimes. The failure mechanism for flash memory cells is analogous to a metal fatigue mode; the device fails by refusing to write new data to specific cells that have been subject to many read-write cycles over the device's lifetime. Premature failure of a "live USB" could be Sony PCG-6Z2M battery,
circumvented by using a flash drive with a write-lock switch as a WORM device, identical to a live CD. Originally, this potential failure mode limited the use of "live USB" system to special-purpose applications or temporary tasks, such as: Sony PCG-6X4M battery,
Loading a minimal, hardened kernel for embedded applications (e.g., network router, firewall).
Bootstrapping an operating system install or disk cloning operation, often across a network.
Maintenance tasks, such as virus scanning or low-level data repair, without the primary host operating system loaded.
As of 2011, newer flash memory designs have much higher estimated lifetimes. Several manufacturers are now offering warranties of 5 years or more. Such warranties should make the device more attractive for more applications. By reducing the probability of the device's premature failure, flash memory devices can now be Sony PCG-4Q2M battery
considered for use where a magnetic disk would normally have been required. Flash drives have also experienced an exponential growth in their storage capacity over time (following the Moore's Law growth curve). As of 2011,
Sony PCG-61813M batterysingle packaged devices with capacities of 64GB are readily available, and devices with 8 GB capacity are very economical. Storage capacities in this range have traditionally been considered to offer adequate space, because they allow enough space for both the operating system software and some free space for the user's data. Sony PCG-4R1M battery
Windows Vista, Windows 7 and Windows 8 ReadyBoost[edit source | editbeta]
In Windows Vista, Windows 7, and Windows 8, the ReadyBoost feature allows flash drives (from 4 GB in the case of Windows Vista) to augment operating system memory.[40] Sony PCG-4Q1M battery
Audio players[edit source | editbeta]
Many companies make small solid-state digital audio players, essentially producing flash drives with sound output and a simple user interface. Examples include the Creative MuVo, Philips GoGear and the first generation iPod shuffle. Some of these players are true USB flash drives as well as music players; others do not support
Sony PCG-61611M batterygeneral-purpose data storage. Other applications requiring storage, such as digital voice or sound recording, can also be combined with flash drive functionality.[41]
Many of the smallest players are powered by a permanently fitted rechargeable battery, charged from the USB interface. Fancier devices that function as a digital audio player have a USB host port (type A female typically).
Media storage and marketing[edit source | editbeta] Sony PCG-71C11M battery
Digital audio files can be transported from one computer to another like any other file, and played on a compatible media player (with caveats for DRM-locked files). In addition, many home Hi-Fi and car stereo head units are now equipped with a USB port. Sony PCG-71D14M battery
Sony PCG-61511M batteryThis allows a USB flash drive containing media files in a variety of formats to be played directly on devices which support the format. Some LCD monitors for consumer HDTV viewing have a dedicated USB port through which music and video files can also be played without use of a personal computer. Sony VGP-BPS12/Q Battery
Artists have sold or given away USB flash drives, with the first instance believed to be in 2004 when the German band WIZO released the "Stick EP", only as a USB drive. In addition to five high-bitrate MP3s, it also included a video, pictures, lyrics, and guitar tablature. Subsequently, artists including Kanye West,[4Sony VGP-BPS13 Battery
2] Nine Inch Nails, Kylie Minogue[43] and Ayumi Hamasaki[44] have released music and promotional material on USB flash drives. In 2009 a USB drive holding fourteen remastered Beatles albums in both FLAC and MP3 was released. Sony VGP-BPS13A Battery
Arcades[edit source | editbeta]
In the arcade game In the Groove and more commonly In The Groove 2, flash drives are used to transfer high scores, screenshots, dance edits, and combos throughout sessions. As of software revision 21 (R21), players can also store custom songs and play them on any machine on which this feature is enabled. While use of flash drives is common, the drive must be Linux compatible. Sony VGP-BPS13A/B Battery
In the arcade games Pump it Up NX2 and Pump it Up NXA, a specially produced flash drive is used as a "save file" for unlocked songs, as well as for progressing in the WorldMax and Brain Shower sections of the game. Sony VGP-BPS13B/B Battery
In the arcade game Dance Dance Revolution X, an exclusive USB flash drive was made by Konami for the purpose of the link feature from its Sony PlayStation 2 counterpart. However, any USB flash drives can be used in this arcade game. Sony VGP-BPS13/B Battery
Brand and product promotion[edit source | editbeta]
Ubuntu-branded USB flash drive and lanyard.
The availability of inexpensive flash drives has enabled them to be used for promotional and marketing purposes, particularly within technical and computer-industry circles (e.g., technology trade shows). They may be given away for free, sold at less than wholesale price, or included as a bonus with another purchased product. Sony VGP-BPS13B/S Battery
Usually, such drives will be custom-stamped with a company's logo, as a form of advertising. The drive may be blank, or preloaded with graphics, documentation, web links, Flash animation or other multimedia, and free or demonstration software. Some preloaded drives are read-only, while others are configured with both read-only and user-writable segments. Such dual-partition drives are more expensive.[45] Sony VGP-BPS13B/Q Battery
Flash drives can be set up to automatically launch stored presentations, websites, articles, and any other software immediately on insertion of the drive using the Microsoft Windows AutoRun feature.[46] Autorunning software this way does not work on all computers, and it is normally disabled by security-conscious users. Sony VGP-BPS13/Q Battery
Backup[edit source | editbeta]
Some value-added resellers are now using a flash drive as part of small-business turnkey solutions (e.g., point-of-sale systems). The drive is used as a backup medium: at the close of business each night, the drive is inserted, and a database backup is saved to the drive. Alternatively, the drive can be left inserted through the business day, and data regularly updated. In either case, the drive is removed at night and taken offsite. Sony VGP-BSP13/S Battery
This is simple for the end-user, and more likely to be done
The drive is small and convenient, and more likely to be carried off-site for safety
The drives are less fragile mechanically and magnetically than tapes
The capacity is often large enough for several backup images of critical data
Flash drives are cheaper than many other backup systems Sony VGP-BPS14 Battery
Flash drives also have disadvantages. They are easy to lose. And it may be easy for unauthorized people to make backups. A lesser setback for flash drives is that they have only one tenth the capacity of hard drives manufactured around their time of distribution. Sony VGP-BPS14/B Battery
Operating system installation media[edit source | editbeta]
Some operating systems can be installed from a flash drive instead of a CD or DVD. Such operating systems include some Linux distributions, Windows 7, Windows 8, and Mac OS X. In particular, Mac OS X 10.7 is distributed only online (through the Mac App Store) or on flash drives. If one has a MacBook Air with Boot Camp and no external optical drive, they can use a flash drive to install Windows. Sony VGP-BPS14B Battery
Security systems[edit source | editbeta]
Windows Vista uses flash drives as certificate carriers for BitLocker encryption on system drives, on systems which do not support TPMs. Some software uses flash drives with hidden data as an offline activation method.
Advantages and disadvantages[edit source | editbeta] Sony VGP-BPS14/S Battery
Flash drives use little power, have no fragile moving parts, and for most capacities are small and light. Data stored on flash drives is impervious to mechanical shock, magnetic fields, scratches and dust. These properties make them suitable for transporting data from place to place and keeping the data readily at hand. Sony PCG-4121DM battery
Flash drives also store data densely compared to many removable media. In mid-2009, 256 GB drives became available, with the ability to hold many times more data than a DVD or even a Blu-ray disc.[2] Sony PCG-4121EM battery
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Most personal computers support USB as of 2012. Flash drives implement the USB mass storage device class so that most modern operating systems can read and write to them without installing device drivers. The flash drives present a simple block-structured logical unit to the host operating system, Sony PCG-41218M battery
Sony PCG-41218M batteryhiding the individual complex implementation details of the various underlying flash memory devices. The operating system can use any file system or block addressing scheme. Some computers can boot up from flash drives. Sony PCG-41213M battery
Specially manufactured flash drives are available that have a tough rubber or metal casing designed to be waterproof and virtually "unbreakable". These flash drives retain their memory after being submerged in water, and even through a machine wash. Leaving such a flash drive out to dry completely before allowing current to run through it has been known to result in a working drive with no future problems. Sony PCG-41414M battery
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Channel Five's Gadget Show cooked one of these flash drives with propane, froze it with dry ice, submerged it in various acidic liquids, ran over it with a jeep and fired it against a wall with a mortar. A company specializing in recovering lost data from computer drives managed to recover all the data on the drive.[47] All data on the other removable storage devices tested, using optical or magnetic technologies, were destroyed. Sony PCG-4121GM battery
Disadvantages[edit source | editbeta]
Main article: Flash memory#Limitations
Like all flash memory devices, flash drives can sustain only a limited number of write and erase cycles before the drive fails.[48][unreliable source?][49] This should be a consideration when using a flash drive to run application software or an operating system. To address this, Sony PCG-41212M battery
Sony PCG-41215M battery as well as space limitations, some developers have produced special versions of operating systems (such as Linux in Live USB)[50] or commonplace applications (such as Mozilla Firefox) designed to run from flash drives. Sony PCG-41311M battery
These are typically optimized for size and configured to place temporary or intermediate files in the computer's main RAM rather than store them temporarily on the flash drive. Sony PCG-41313M battery
A few USB flash drives include a write-protect mechanism consisting of a switch, on the housing of the drive itself, that prevents the host computer from writing or modifying data on the drive. This feature is becoming less common. Sony PCG-41314M battery
Write-protection makes a device suitable for repairing virus-contaminated host computers without risk of infecting the USB flash drive itself. A write-locked SD card in a USB flash card reader adapter is an effective way to avoid any writes on the flash medium. The SD card as a Write Once Read Many device has an essentially unlimited life. Sony PCG-41315M battery
A drawback to the small size of flash drives is that they are easily misplaced, left behind, or otherwise lost. This is a particular problem if the data they contain are sensitive (see data security). As a consequence, some manufacturers have added encryption hardware to their drives—although software encryption systems which can be used in conjunction with any mass storage medium achieve the same thing. Most drives can be attached to keychains, necklaces and lanyards. Sony PCG-4R2M battery
Sony PCG-6122M batteryThe USB plug is usually fitted with a removable and easily lost protective cap, or is retractable.
USB flash drives are more expensive per unit of storage than large hard drives, but are less expensive in capacities of a few tens of gigabytes as of 2011.[51][52] Maximum available capacity is increasing with time, but is less than larger hard drives. This balance is changing, but the rate of change is slowing. Sony PCG-4R2M battery
Most USB-based flash technology integrates a printed circuit board with a metal tip, which is simply soldered on. As a result, the stress point is where the two pieces join. The quality control of some manufacturers does not ensure a proper solder temperature, further weakening the stress point.[53] Sony PCG-4U2M battery
[54] Since many flash drives stick out from computers, they are likely to be bumped repeatedly and may break at the stress point. Most of the time, a break at the stress point tears the joint from the printed circuit board and results in permanent damage. However, some manufacturers produce [5Sony PCG-6Z4M battery
Sony PCG-6112M battery5] discreet flash drives that do not stick out, and others use a [56] solid metal uni-body that has no easily discernible stress point.
Comparison with other portable storage[edit source | editbeta]
Punched cards in storage at a U.S. Federal records center in 1959. All the data visible here could fit on a 4 GB flash drive (with minimal ZIP compression).
Tape[edit source | editbeta]
The applications of current data tape cartridges hardly overlap those of flash drives: on tape, cost per gigabyte is very low for large volumes, but the individual drives and media are expensive. Media has a very high capacity and very fast transfer speeds, but store data sequentially and is very slow for random access of data. Sony VGP-BPL14 battery
Sony VGP-BPS12/Q battery While disk-based backup is now the primary medium of choice for most companies, tape backup is still popular for taking data off-site for worst-case scenarios and for very large volumes (more than a few hundreds of TB). See LTO tapes. Sony VGP-BPL14/B battery
Floppy disk[edit source | editbeta]
Size comparison of a flash drive and a 3.5-inch floppy disk. The flash drive can hold about 11,380 times more data.
Floppy disk drives are rarely fitted to modern computers and are obsolete for normal purposes, although internal and external drives can be fitted if required. Floppy disks may be the method of choice for transferring data to and from very old computers without USB or booting from floppy disks, Sony VGP-BPS14 battery
Sony VGP-BPS12 battery and so they are sometimes used to change the firmware on, for example, BIOS chips. Devices with removable storage like older Yamaha music keyboards are also dependent on floppy disks, which require computers to process them. Newer devices are built with USB flash drive support. Sony VGP-BPS14/S battery
Optical media[edit source | editbeta]
The various writable and rewritable forms of CD and DVD are portable storage media supported by the vast majority of computers as of 2008. CD-R, DVD-R, and DVD+R can be written to only once, RW varieties up to about 1,000 erase/write cycles, while modern NAND-based flash drives often last for 500,000 or more erase/write cycles.[57] DVD-RAM discs are the most suitable optical discs for data storage involving much rewriting.
Optical storage devices are among the cheapest methods of mass data storage after the hard drive. They are slower than their flash-based counterparts. Standard 12 cm optical discs are larger than flash drives and more subject to damage. Smaller optical media do exist, Sony VGN-Z11MN/B battery
such as business card CD-Rs which have the same dimensions as a credit card, and the slightly less convenient but higher capacity 8 cm recordable MiniCD and MiniDVD. The small discs are more expensive than the standard size, and do not work in all drives. Sony VGN-Z11WN/B battery
Universal Disk Format (UDF) version 1.50 and above has facilities to support rewritable discs like sparing tables and virtual allocation tables, spreading usage over the entire surface of a disc and maximising life, but many older operating systems do not support this format. Sony VGN-Z21 battery
Sony VGN-Z51XG batteryPacket-writing utilities such as DirectCD and InCD are available but produce discs that are not universally readable (although based on the UDF standard). The Mount Rainier standard addresses this shortcoming in CD-RW media by running the older file systems on top of it and performing defect management for those standards, but it requires support from both the CD/DVD burner and the operating system.
Sony VGN-Z51WG batteryMany drives made today do not support Mount Rainier, and many older operating systems such as Windows XP and below, and Linux kernels older than 2.6.2, do not support it (later versions do). Essentially CDs/DVDs are a good way to record a great deal of information cheaply and have the advantage of being readable by most standalone players, Sony VGN-Z21MN/B battery
Sony VGN-Z31ZN/B battery but they are poor at making ongoing small changes to a large collection of information. Flash drives' ability to do this is their major advantage over optical media.
Flash memory cards[edit source | editbeta]
Flash memory cards, e.g., Secure Digital cards, are available in various formats and capacities, and are used by many consumer devices. However, while virtually all PCs have USB ports, Sony VGN-Z21XN battery
Sony VGN-Z31WN/B batteryallowing the use of USB flash drives, memory card readers are not commonly supplied as standard equipment (particularly with desktop computers). Although inexpensive card readers are available that read many common formats, this results in two pieces of portable equipment (card plus reader) rather than one. Sony VGN-Z21ZN/X battery
Some manufacturers, aiming at a "best of both worlds" solution, have produced card readers that approach the size and form of USB flash drives (e.g., Kingston MobileLite,[58] SanDisk MobileMate[59]) These readers are limited to a specific subset of memory card formats (such as SD, microSD, or Memory Stick), Sony VGN-Z31 battery
Sony VGN-Z31VN/X battery and often completely enclose the card, offering durability and portability approaching, if not quite equal to, that of a flash drive. Although the combined cost of a mini-reader and a memory card is usually slightly higher than a USB flash drive of comparable capacity, the reader + card solution offers additional flexibility of use, and virtually "unlimited" capacity. Sony PCG-41212M battery
Sony PCG-6124M battery The ubiquity of SD cards is such that, circa 2011, due to economies of scale, their price is now less than an equivalent-capacity USB flash drive, even with the added $2 (Canadian) cost of a USB SD card reader.
An additional advantage of memory cards is that many consumer devices (e.g., digital cameras, portable music players) cannot make use of USB flash drives (even if the device has a USB port), whereas the memory cards used by the devices can be read by PCs with a card reader. Sony PCG-41216M battery
External hard disk[edit source | editbeta]
Particularly with the advent of USB, external hard disks have become widely available and inexpensive. External hard disk drives currently cost less per gigabyte than flash drives and are available in larger capacities. Some hard drives support alternative and faster interfaces than USB 2.0 (e.g., Sony PCG-41217M battery
IEEE 1394 and eSATA). For consecutive sector writes and reads (for example, from an unfragmented file), most hard drives can provide a much higher sustained data rate than current NAND flash memory, though mechanical latencies seriously impact hard drive performance. Sony PCG-41218M battery
Unlike solid-state memory, hard drives are susceptible to damage by shock (e.g., a short fall) and vibration, have limitations on use at high altitude, and although they are shielded by their casings, they are vulnerable when exposed to strong magnetic fields. In terms of overall mass, Sony PCG-31111M battery
Sony PCG-6112M batteryhard drives are usually larger and heavier than flash drives; however, hard disks sometimes weigh less per unit of storage. Like flash drives, hard disks also suffer from file fragmentation, which can reduce access speed. Sony PCG-31112M battery
Obsolete devices[edit source | editbeta]
Audio tape cassettes and high-capacity floppy disks (e.g., Imation SuperDisk), and other forms of drives with removable magnetic media, such as the Iomega Zip and Jaz drives, Sony PCG-31113M battery
are now largely obsolete and rarely used. There are products in today's market that will emulate these legacy drives for both tape and disk (SCSI1/SCSI2, SASI, Magneto optic, Ricoh ZIP, Jaz, IBM3590/ Fujitsu 3490E and Bernoulli for example) in state-of-the-art Compact Flash storage devices – CF2SCSI.
Encryption and Security[edit source | editbeta]
Main article: USB flash drive security
As highly portable media, USB flash drives are easily lost or stolen. All USB flash drives can have their contents encrypted using third-party disk encryption software, which can often be run directly from the USB drive without installation (for example, FreeOTFE), although some, such as TrueCrypt, require the user to have administrative rights on every computer it's run on. Sony PCG-6X2M battery,
Archiving software can achieve a similar result by creating encrypted ZIP or RAR files.
Some manufacturers have produced USB flash drives which use hardware-based encryption as part of the design,[60] removing the need for third-party encryption software. In limited circumstances these drives have been shown to have security problems, and are typically more expensive than software-based systems, which are available for free. Sony PCG-41311M battery
A minority of flash drives support biometric fingerprinting to confirm the user's identity. As of mid-2005,[dated info] this was an expensive alternative to standard password protection offered on many new USB flash storage devices.
Sony PCG-4R2M batteryMost fingerprint scanning drives rely upon the host operating system to validate the fingerprint via a software driver, often restricting the drive to Microsoft Windows computers. However, there are USB drives with fingerprint scanners which use controllers that allow access to protected data without any authentication.[61] Sony PCG-4R1M battery
Some manufacturers deploy physical authentication tokens in the form of a flash drive. These are used to control access to a sensitive system by containing encryption keys or, more commonly, communicating with security software on the target machine.
Sony PCG-4R2M batteryThe system is designed so the target machine will not operate except when the flash drive device is plugged into it. Some of these "PC lock" devices also function as normal flash drives when plugged into other machines. Sony PCG-41313M battery
Security threats[edit source | editbeta]
Flash drives may present a significant security challenge for some organizations. Their small size and ease of use allows unsupervised visitors or employees to store and smuggle out confidential data with little chance of detection. Both corporate and public computers are vulnerable to attackers connecting a flash drive to a free USB port and using malicious software such as keyboard loggers or packet sniffers. Sony PCG-71C11M battery
For computers set up to be bootable from a USB drive, it is possible to use a flash drive containing a bootable portable operating system to access the files of the computer
Sony PCG-41315M batteryeven if the computer is password protected. The password can then be changed, or it may be possible to crack the password with a password cracking program and gain full control over the computer. Encrypting files provides considerable protection against this type of attack. Sony PCG-61511M battery
USB flash drives may also be used deliberately or unwittingly to transfer malware and autorun worms onto a network.
Some organizations forbid the use of flash drives, and some computers are configured to disable the mounting of USB mass storage devices by users other than administrators; others use third-party software to control USB usage. The use of software allows the administrator to not only provide a USB lock but also control the use of CD-RW, , Sony PCG-41314M battery SD cards and other memory devices. This enables companies with policies forbidding the use of USB flash drives in the workplace to enforce these policies. In a lower-tech security solution, some organizations disconnect USB ports inside the computer or fill the USB sockets with epoxy. Sony PCG-61712M battery
Some of the security measures taken to prevent confidential data from being taken have presented some side effects such as curtailing user privileges of recharging mobile devices off the USB ports on the systems.
Naming[edit source | editbeta] Sony VPCSE2V9E battery
In 2005, Microsoft was using the term "USB Flash Drive" as the common name for these devices when they introduced the Microsoft USB Flash Drive Manager application.[62] Alternative names are commonly used, many of which are trademarks of various manufacturers. Sony PCG-4121DM battery
Sony PCG-4121GM battery
Current and future developments[edit source | editbeta]
The internals of a 32 GB Toshiba USB 3.0 Flash Drive. The USB 3.0 standard is becoming increasingly popular. This drive has a write speed of 60 MB/s and a read speed of 120 MB/s, making it faster than the USB 2.0 standard. Sony PCG-71411M battery
Semiconductor corporations have worked to reduce the cost of the components in a flash drive by integrating various flash drive functions in a single chip, thereby reducing the part-count and overall package-cost. Sony PCG-4121EM battery
Flash drive capacities on the market increase continually. As of 2010, few manufacturers continue to produce models of 1 GB and smaller, and many have started to phase out 2 GB capacity flash memory. High speed has become a standard for modern flash drives. Capacities of up to 256 GB have come on the market, as of 2009.[2]
Sony PCG-41214M battery
Lexar is attempting to introduce a USB FlashCard, which would be a compact USB flash drive intended to replace various kinds of flash memory cards. Pretec introduced a similar card, which also plugs into any USB port, but is just one quarter the thickness of the Lexar model.[63] Until 2008, SanDisk manufactured a product called SD Plus, which was a SecureDigital card with a USB connector.[64] Sony PCG-71511M battery
SanDisk has also introduced a new technology to allow controlled storage and usage of copyrighted materials on flash drives, primarily for use by students. This technology is termed FlashCP.
A hard disk drive (HDD)[note 2] is a data storage device used for storing and retrieving digital information using rapidly rotating disks (platters) coated with magnetic material. An HDD retains its data even when powered off. Data is read in a random-access manner, Sony SVS13AA11L Battery
Sony PCG-41414L Battery meaning individual blocks of data can be stored or retrieved in any order rather than sequentially. An HDD consists of one or more rigid ("hard") rapidly rotating disks (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.
Sony PCG-41413L Battery
Introduced by IBM in 1956,[2] HDDs became the dominant secondary storage device for general purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and personal computers. More than 200 companies have produced HDD units, Sony SVS131A11L Battery
Sony PCG-41412L Batterythough most current units are manufactured by Seagate, Toshiba and Western Digital. Worldwide revenues for HDDs shipments are expected to reach $33 billion in 2013, a decrease of about 12% from $37.8 billion in 2012. Sony SVS131B11L Battery
The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Sony SVS151A11L Battery
Sony PCG-41218L Battery Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and
Sony PCG-41414M batteryrecovery. Performance is specified by the time to move the heads to a file (Average Access Time) plus the time it takes for the file to move under its head (average latency,
Sony PCG-41217L Batterya function of the physical rotational speed in revolutions per minute) and the speed at which the file is transmitted (data rate).
The two most common form factors for modern HDDs are 3.5-inch in desktop computers and 2.5-inch in laptops. HDDs are connected to systems by standard interface cables such as SATA (Serial ATA), USB or SAS (Serial attached SCSI) cables. Sony SVS151B11L Battery
As of 2012, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs). HDDs are expected to remain the dominant medium for secondary storage due to predicted continuing advantages in recording capacity and price per unit of storage;[3][4] Sony SVS151G1GL Battery
Sony PCG-4121DL Battery
but SSDs are replacing HDDs where speed, power consumption and durability are more important considerations than price and capacity.[5][6]
HDDs were introduced in 1956 as data storage for an IBM real-time transaction processing computer[2] and were developed for use with general purpose mainframe and minicomputers. The first IBM drive, the 350 RAMAC, Sony PCG-4121EL Battery
Sony PCG-41215L Battery was approximately the size of two refrigerators and stored 5 million 6-bit characters (the equivalent of 3.75 million 8-bit bytes) on a stack of 50 disks. Sony PCG-4121FL Battery
In 1961 IBM introduced the model 1311 disk drive, which was about the size of a washing machine and stored two million characters on a removable disk pack. Users could buy additional packs and interchange them as needed, Sony PCG-4121GL Battery
Sony PCG-41214L Batterymuch like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Non-removable HDDs were called fixed disk drives. Sony PCG-41211L Battery
Some high performance HDDs were manufactured with one head per track, e.g., IBM 2305 so that no time was lost physically moving the heads to a track.[7] Known as Fixed-Head or Head-Per-Track disk drives they were very expensive and are no longer in production.[8] Sony PCG-41212L Battery
In 1973, IBM introduced a new type of HDD codenamed "Winchester". Its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Sony PCG-41213L Battery Instead, the heads were allowed to "land" on a special area of the disk surface upon spin-down, "taking off" again when the disk was later powered on. Sony PCG-41211M battery
This greatly reduced the cost of the head actuator mechanism, but precluded removing just the disks from the drive as was done with the disk packs of the day. sony PCG-4R2L battery
sony PCG-6Z4L batteryInstead, the first models of "Winchester technology" drives featured a removable disk module, which included both the disk pack and the head assembly, leaving the actuator motor in the drive upon removal. Later "Winchester" drives abandoned the removable media concept and returned to non-removable platters. sony PCG-4R1L battery
Like the first removable pack drive, the first "Winchester" drives used platters 14 inches (360 mm) in diameter. A few years later, designers were exploring the possibility that physically smaller platters might offer advantages. sony PCG-4Q3L battery
sony PCG-6Z3L batteryDrives with non-removable eight-inch platters appeared, and then drives that used a 5 1⁄4 in (130 mm) form factor (a mounting width equivalent to that used by contemporary floppy disk drives). The latter were primarily intended for the then-fledgling personal computer (PC) market. Sony PCG-41213M battery
Sony PCG-41218M battery
As the 1980s began, HDDs were a rare and very expensive additional feature on PCs; however by the late 1980s, their cost had been reduced to the point where they were standard on all but the cheapest PC.
Most HDDs in the early 1980s were sold to PC end users as an external, add-on subsystem. The subsystem was not sold under the drive manufacturer's name but under the subsystem manufacturer's name such as Corvus Systems and Tallgrass Technologies, sony PCG-4Q1L battery
sony PCG-6XBL batteryor under the PC system manufacturer's name such as the Apple ProFile. The IBM PC/XT in 1983 included an internal 10MB HDD, and soon thereafter internal HDDs proliferated on personal computers. sony PCG-6X1L battery
External HDDs remained popular for much longer on the Apple Macintosh. Every Mac made between 1986 and 1998 has a SCSI port on the back, making external expansion easy; also, "toaster" Compact Macs did not have easily accessible HDD bays (or, in the case of the Mac Plus,
sony PCG-6X8L batteryany hard drive bay at all), so on those models, external SCSI disks were the only reasonable option.
Driven by areal density doubling every two to four years since their invention (an observation known as Kryder's law, similar to Moore's Law), HDDs have continuously improved their characteristics; a few highlights include: sony PCG-6X2L battery
Capacity per HDD increasing from 3.75 megabytes[2] to 4 terabytes or more, more than a million times larger.
Physical volume of HDD decreasing from 68 cubic feet (1.9 m3)[2] (comparable to a large side-by-side refrigerator), to less than 20 millilitres (0.70 imp fl oz; 0.68 US fl oz),[9] a 100,000-to-1 decrease. Sony PCG-61A11L Battery
Weight decreasing from 2,000 pounds (910 kg)[2] to 48 grams (1.7 oz),[9] a 20,000-to-1 decrease.
Price decreasing from about US$15,000 per megabyte[10] to less than $0.00006 per megabyte ($90/1.5 terabyte), a greater than 250-million-to-1 decrease.[11] Sony PCG-61A13L Battery
Average Access Time decreasing from over 100 milliseconds to a few milliseconds, a greater than 40-to-1 improvement.
Market application expanding from mainframe computers of the late 1950s to most mass storage applications including computers and consumer applications such as storage of entertainment content.
Sony PCG-71914L Battery
Technology[edit source | editbeta]
Magnetic cross section & frequency modulation encoded binary data
Magnetic recording[edit source | editbeta]
See also: Magnetic storage
An HDD records data by magnetizing a thin film of ferromagnetic material[note 3] on a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. Sony PCG-61A14L Battery
Sony PCG-71C11L Battery
User data is encoded using an encoding scheme, such as run-length limited encoding,[note 4] which determines how the data is represented by the magnetic transitions.
A typical HDD design consists of a spindle that holds flat circular disks, also called platters, which hold the recorded data. The platters are made from a non-magnetic material, usually aluminium alloy, glass, or ceramic, Sony PCG-71C12L Battery
Sony PCG-71913L Batteryand are coated with a shallow layer of magnetic material typically 10–20 nm in depth, with an outer layer of carbon for protection.[13][14][15] For reference, a standard piece of copy paper is 0.07–0.18 millimetre (70,000–180,000 nm).[16] Sony PCG-61714L Battery
Diagram labeling the major components of a computer HDD
Recording of single magnetisations of bits on a 200MB HDD-platter (recording made visible using CMOS-MagView).[17]
Longitudinal recording (standard) & perpendicular recording diagram
The platters in contemporary HDDs are spun at speeds varying from 4,200 rpm in energy-efficient portable devices, to 15,000 rpm for high performance servers.[18] The first HDDs spun at 1,200 rpm[2] and, for many years, 3,600 rpm was the norm.[19] Sony PCG-61813L Battery
Today, the platters in most consumer HDDs spin in the range of 5,400 rpm to 7,200 rpm.
Information is written to and read from a platter as it rotates past devices called read-and-write heads that operate very close (often tens of nanometers) over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it.
Sony PCG-71912L Battery
In modern drives there is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins.
Sony PCG-71911L BatteryThe arm is moved using a voice coil actuator or in some older designs a stepper motor. Early hard disk drives wrote data at some constant bits per second, resulting in all tracks having the same amount of data per track but modern drives (since the 1990s) Sony PCG-61911L Battery
Sony PCG-71811L Battery use zone bit recording—increasing the write speed from inner to outer zone and thereby storing more data per track in the outer zones.
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects. Sony PCG-61913L Battery
To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other.[ Sony PCG-71614L Battery
Sony PCG-71713L Battery20] Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005,[21] and as of 2007 the technology was used in many HDDs.[22][23][24] Sony PCG-61713L Battery
Components[edit source | editbeta]
HDD with disks and motor hub removed exposing copper colored stator coils surrounding a bearing in the center of the spindle motor. Orange stripe along the side of the arm is thin printed-circuit cable, spindle bearing is in the center and the actuator is in the upper left
Sony PCG-61316L Battery
A typical HDD has two electric motors; a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; Sony PCG-91111L Battery
Sony PCG-91112L Battery
Sony PCG-61315L Batterythe stator windings are fixed in place. Opposite the actuator at the end of the head support arm is the read-write head; thin printed-circuit cables connect the read-write heads to amplifier electronics mounted at the pivot of the actuator. The head support arm is very light, but also stiff; in modern drives, acceleration at the head reaches 550 g. Sony PCG-71312L Battery
Head stack with an actuator coil on the left and read/write heads on the right
The actuator is a permanent magnet and moving coil motor that swings the heads to the desired position. A metal plate supports a squat neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate is the moving coil, Sony PCG-71311L Battery
often referred to as the voice coil by analogy to the coil in loudspeakers, which is attached to the actuator hub, and beneath that is a second NIB magnet, mounted on the bottom plate of the motor (some drives only have one magnet). Sony PCG-71218L Battery
The voice coil itself is shaped rather like an arrowhead, and made of doubly coated copper magnet wire. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it is wound on a form, Sony PCG-71217L Battery
Sony PCG-61312L Battery making it self-supporting. The portions of the coil along the two sides of the arrowhead (which point to the actuator bearing center) interact with the magnetic field, developing a tangential force that rotates the actuator. Current flowing radially outward along one side of the arrowhead and radially inward on the other produces the tangential force. Sony PCG-71313L Battery
Sony PCG-61311L Battery If the magnetic field were uniform, each side would generate opposing forces that would cancel each other out. Therefore the surface of the magnet is half N pole, half S pole, with the radial dividing line in the middle, Sony PCG-71315L Battery
Sony PCG-61215L Batterycausing the two sides of the coil to see opposite magnetic fields and produce forces that add instead of canceling. Currents along the top and bottom of the coil produce radial forces that do not rotate the head. Sony PCG-71316L Battery
The HDD's electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the disk controller. Feedback of the drive electronics is accomplished by means of special segments of the disk dedicated to servo feedback. These are either complete concentric circles (in the case of dedicated servo technology), Sony PCG-71317L Battery
Sony PCG-71216L Battery or segments interspersed with real data (in the case of embedded servo technology). The servo feedback optimizes the signal to noise ratio of the GMR sensors by adjusting the voice-coil of the actuated arm. Sony PCG-71318L Battery
Sony PCG-71215L Battery The spinning of the disk also uses a servo motor. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed. Sony PCG-71211L Battery
Error handling[edit source | editbeta]
Modern drives make extensive use of error correction codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, Sony PCG-71212L Battery but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity.[25] In the newest drives of 2009, low-density parity-check codes (LDPC) were supplanting Reed-Solomon; LDPC codes enable performance close to the Shannon Limit and thus provide the highest storage density available.[26] Sony PCG-3B1L Battery
Sony PCG-3B2L Battery
Typical HDDs attempt to "remap" the data in a physical sector that is failing to a spare physical sector—hopefully while the errors in the bad sector are still few enough that the ECC can recover the data without loss. The S.M.A.R.T-Self-Monitoring, Sony PCG-3B3L Battery
Sony PCG-3H4L BatteryAnalysis and Reporting Technology system counts the total number of errors in the entire HDD fixed by ECC and the total number of remappings, as the occurrence of many such errors may predict HDD failure. Sony PCG-3B4L Battery
Future development[edit source | editbeta]
HDD areal densities have shown a long term compound annual growth rate not substantively different from Moore's Law, most recently in the range of 20-25% annually, with desktop 3.5" drives estimated to hit 12 TB around 2016. Sony PCG-3C2L Battery
[27] New magnetic storage technologies are being developed to support higher areal density growth and maintain the competitiveness of HDDs with potentially competitive products such as flash memory-based solid-state drives (SSDs). These new HDD technologies include:
Heat-assisted magnetic recording (HAMR)[28][29] Sony PCG-3C3L Battery
Sony PCG-3D3L Battery
Bit-patterned recording (BPR)[30]
Current Perpendicular to Plane giant magnetoresistance (CPP/GMR) heads[27]
Shingled Write[27]
With these new technologies the relative position of HDDs and SSDs with regard to their cost and performance is not projected to change through 2016.[27]
Capacity[edit source | editbeta] Sony PCG-3D4L Battery
The capacity of an HDD reported to an end user by the operating system is less than the amount stated by a drive or system manufacturer due to amongst other things, different units of measuring capacity, capacity consumed by the file system and/or redundancy.
Calculation[edit source | editbeta] Sony PCG-3E3L Battery
Because modern disk drives appear to their interface as a contiguous set of logical blocks their gross capacity can be calculated by multiplying the number of blocks by the size of the block. This information is available from the manufacturer's specification and from the drive itself through use of special utilities invoking low level commands.[31][32] Sony PCG-3F1L Battery
The gross capacity of older HDDs can be calculated by multiplying for each zone of the drive the number of cylinders by the number of heads by the number of sectors/zone by the number of bytes/sector (most commonly 512) and then summing the totals for all zones. Some modern SATA drives will also report cylinder-head-sector (C/H/S) Sony PCG-3F2L Battery
Sony PCG-3G3L Battery values to the CPU but they are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces.
The old C/H/S scheme has been replaced by logical block addressing. In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no modern drive has anywhere near 32 platters. Sony PCG-3F3L Battery
In modern HDDs, spare capacity for defect management is not included in the published capacity; however in many early HDDs a certain number of sectors were reserved for spares, thereby reducing capacity available to end users. Sony PCG-3F4L Battery
In some systems, there may be hidden partitions used for system recovery that reduce the capacity available to the end user.
For RAID subsystems, data integrity and fault-tolerance requirements also reduce the realized capacity. For example, a RAID1 subsystem will be about half the total capacity as a result of data mirroring. RAID5 subsystems with x drives, Sony PCG-9Z1L Battery
Sony PCG-7185L Batterywould lose 1/x of capacity to parity. RAID subsystems are multiple drives that appear to be one drive or more drives to the user, but provides a great deal of fault-tolerance. Most RAID vendors use some form of checksums to improve data integrity at the block level. Sony PCG-9Z2L Battery
For many vendors, this involves using HDDs with sectors of 520 bytes per sector to contain 512 bytes of user data and eight checksum bytes or using separate 512-byte sectors for the checksum data.[33] Sony PCG-7142L Battery
File system use[edit source | editbeta]
Main article: Disk formatting
The presentation of an HDD to its host is determined by its controller. This may differ substantially from the drive's native interface particularly in mainframes or servers.
Modern HDDs, such as SAS[31] and SATA[32] drives, appear at their interfaces as a contiguous set of logical blocks; typically 512 bytes long but the industry is in the process of changing to 4,096-byte logical blocks; see Advanced Format.[34] Sony PCG-7151L Battery
Sony PCG-7152L Battery
The process of initializing these logical blocks on the physical disk platters is called low level formatting which is usually performed at the factory and is not normally changed in the field.[note 5]
Sony PCG-7183L Battery
High level formatting then writes the file system structures into selected logical blocks to make the remaining logical blocks available to the host OS and its applications.[35] The operating system file system uses some of the disk space to organize files on the disk, recording their file names and the sequence of disk areas that represent the file. Sony PCG-7153L Battery
Sony PCG-7182L Battery Examples of data structures stored on disk to retrieve files include the file allocation table (FAT) in the MS-DOS file system and inodes in many UNIX file systems, as well as other operating system data structures. Sony PCG-7154L Battery
Sony PCG-7181L BatteryAs a consequence not all the space on an HDD is available for user files. This file system overhead is usually less than 1% on drives larger than 100 MB.
Units[edit source | editbeta] Sony PCG-7161L Battery
See also: Binary prefix
Unit prefixes[36][37]
The total capacity of HDDs is given by manufacturers in megabytes (1 MB = 1,000,000 bytes), gigabytes (1 GB = 1,000,000,000 bytes) or terabytes (1 TB = 1,000,000,000,000 bytes).
Sony PCG-7173L Battery] This numbering convention, where prefixes like mega- and giga- denote powers of 1,000, is also used for data transmission rates and DVD capacities. However, the convention is different from that used by manufacturers of memory (RAM, ROM) and CDs, where prefixes like kilo- and mega- mean powers of 1,024. Sony PCG-7162L Battery
The practice of using prefixes assigned to powers of 1,000 within the HDD and computer industries dates back to the early days of computing.[43] By the 1970s million, mega and M were consistently being used in the powers of 1,000 sense to describe HDD capacity.[44][45][46] Sony PCG-7171L Battery
Sony PCG-7172L Battery
Computers do not internally represent HDD or memory capacity in powers of 1,024; reporting it in this manner is just a convention.[47] Microsoft Windows uses the powers of 1,024 convention when reporting HDD capacity, Sony PCG-8131L Battery
thus an HDD offered by its manufacturer as a 1 TB drive is reported by these OSes as a 931 GB HDD. Mac OS X 10.6 ("Snow Leopard"), uses powers of 1,000 when reporting HDD capacity.
In the case of "mega-", there is a nearly 5% difference between the powers of 1,000 definition and the powers of 1,024 definition. Furthermore, Sony PCG-8141L Battery
Sony PCG-8151L Battery the difference is compounded by 2.4% with each incrementally larger prefix (gigabyte, terabyte, etc.). The discrepancy between the two conventions for measuring capacity was the subject of several class action suits against HDD manufacturers. The plaintiffs argued that the use of decimal measurements effectively misled consumers[48][49] Sony PCG-71111L Battery
Sony PCG-81111L Battery
Sony PCG-81411L Battery while the defendants denied any wrongdoing or liability, asserting that their marketing and advertising complied in all respects with the law and that no class member sustained any damages or injuries.[50] Sony PCG-81112L Battery
In December 1998, standards organizations addressed these dual definitions of the conventional prefixes by standardizing on unique binary prefixes and prefix symbols to denote multiples of 1,024, such as "mebibyte (MiB)", which exclusively denotes 220 or 1,048,576 bytes.
Sony PCG-81313L Battery [51] This standard has seen little adoption by the computer industry, and the conventionally prefixed forms of "byte" continue to denote slightly different values depending on context.[52][53] Sony PCG-81113L Battery
Form factors[edit source | editbeta]
Six HDDs with 8", 5.25", 3.5", 2.5", 1.8", and 1" hard disks with a ruler to show the length of platters and read-write heads
Mainframe and minicomputer hard disks were of widely varying dimensions, typically in free standing cabinets the size of washing machines or designed to fit a 19" rack. In 1962, IBM introduced its model 1311 disk, Sony PCG-81114L Battery
which used 14 inch (nominal size) platters. This became a standard size for mainframe and minicomputer drives for many years.[65] Such large platters were never used with microprocessor-based systems. Sony PCG-81214L Battery
Sony PCG-81311L Battery
With increasing sales of microcomputers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable. Thus HDD Form factors, initially followed those of 8-inch, 5.25-inch, and 3.5-inch floppy disk drives. Because there were no smaller floppy disk drives, smaller HDD form factors developed from product offerings or industry standards.
8 inchSony VPCF115FM battery
9.5 in × 4.624 in × 14.25 in (241.3 mm × 117.5 mm × 362 mm). In 1979, Shugart Associates' SA1000 was the first form factor compatible HDD, having the same dimensions and a compatible interface to the 8" FDD. Sony VPCF11JFX battery
5.25 inch
5.75 in × 3.25 in × 8 in (146.1 mm × 82.55 mm × 203 mm). This smaller form factor, first used in an HDD by Seagate in 1980,[66] was the same size as full-height 5 1⁄4-inch-diameter (130 mm) FDD, 3.25-inches high. This is twice as high as "half height";Sony VPCF11MFX battery
Sony VPCF114FX battery i.e., 1.63 in (41.4 mm). Most desktop models of drives for optical 120 mm disks (DVD, CD) use the half height 5¼" dimension, but it fell out of fashion for HDDs. The Quantum Bigfoot HDD was the last to use it in the late 1990s, with "low-profile" (≈25 mm) and "ultra-low-profile" (≈20 mm) high versions. Sony VPCF11FGX battery
Sony VPCF113FX battery
3.5 inch
4 in × 1 in × 5.75 in (101.6 mm × 25.4 mm × 146 mm) = 376.77344 cm³. This smaller form factor is similar to that used in an HDD by Rodime in 1983,[67] which was the same size as the "half height" 3½" FDD, i.e., 1.63 inches high. Today, the 1-inch high ("slimline" or "low-profile") version of this form factor is the most popular form used in most desktops. Sony VPCF11LFX battery
Sony VPCF11DGX battery
2.5 inch
2.75 in × 0.275–0.59 in × 3.945 in (69.85 mm × 7–15 mm × 100 mm) = 48.895–104.775 cm3. This smaller form factor was introduced by PrairieTek in 1988;[68] there is no corresponding FDD. It came to be widely used for HDDs in mobile devices (laptops, music players, etc.) and for solid-state drives (SSDs), Sony VPCF117FX battery
Sony VPCF11HGX batteryby 2008 replacing some 3.5 inch enterprise-class drives.[69] It is also used in the PlayStation 3[70] and Xbox 360[citation needed] video game consoles. Drives 9.5 mm high became an unofficial standard for all except the largest-capacity laptop drives (usually having two platters inside); Sony VPCF112FX battery
Sony VPCF11BFX battery 12.5 mm-high drives, typically with three platters, are used for maximum capacity, but will not fit most laptop computers. Enterprise-class drives can have a height up to 15 mm.[71] Seagate released a 7mm drive aimed at entry level laptops and high end netbooks in December 2009.[72] Western Digital released on April 23, 2013 a hard drive 5 mm in height specifically aimed at UltraBooks.[73] Sony VPCF11KFX battery
1.8 inch
54 mm × 8 mm × 71 mm = 30.672 cm³. This form factor, originally introduced by Integral Peripherals in 1993, evolved into the ATA-7 LIF with dimensions as stated. For a time it was increasingly used in digital audio players and subnotebooks, but its popularity decreased to the point where this form factor is increasingly rare and only a small percentage of the overall market.[74]
Sony VPCF1190X battery
1 inch
42.8 mm × 5 mm × 36.4 mm. This form factor was introduced in 1999 as IBM's Microdrive to fit inside a CF Type II slot. Samsung calls the same form factor "1.3 inch" drive in its product literature.[75]
Sony VPCF119GX battery
0.85 inch
24 mm × 5 mm × 32 mm. Toshiba announced this form factor in January 2004[76] for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets. Toshiba manufactured a 4 GB (MK4001MTD) and an 8 GB (MK8003MTD) version[77] and holds the Guinness World Record for the smallest HDD.[78] Sony VPCF11CGX battery
As of 2012, 2.5-inch and 3.5-inch hard disks were the most popular sizes.
By 2009 all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory,[79][80] which has no moving parts.
Sony VPCF11GGX battery
While these sizes are customarily described by an approximately correct figure in inches, actual sizes have long been specified in millimeters.
Performance characteristics[edit source | editbeta]
Sony VPCF111FX battery
Main article: Hard disk drive performance characteristics
Time to access data[edit source | editbeta]
The factors that limit the time to access the data on an HDD are mostly related to the mechanical nature of the rotating disks and moving heads. Seek time is a measure of how long it takes the head assembly to travel to the track of the disk that contains data. Sony VPCF116FX battery Rotational latency is incurred because the desired disk sector may not be directly under the head when data transfer is requested. These two delays are on the order of milliseconds each. The bit rate or data transfer rate (once the head is in the right position) Dell XPS 14 Battery
creates delay which is a function of the number of blocks transferred; typically relatively small, but can be quite long with the transfer of large contiguous files. Delay may also occur if the drive disks are stopped to save energy. Dell XPS 14D Battery
An HDD's Average Access Time is its average Seek time which technically is the time to do all possible seeks divided by the number of all possible seeks, but in practice is determined by statistical methods or simply approximated as the time of a seek over one-third of the number of tracks.[81]
Defragmentation is a procedure used to minimize delay in retrieving data by moving related items to physically proximate areas on the disk.[82] Some computer operating systems perform defragmentation automatically. Although automatic defragmentation is intended to reduce access delays, performance will be temporarily reduced while the procedure is in progress.[
Time to access data can be improved by increasing rotational speed (thus reducing latency) and/or by reducing the time spent seeking. Increasing areal density increases throughput by increasing data rate and by increasing the amount of data under a set of heads, Dell XPS 14D-L401X Battery
Dell XPS 17-L702X Batterythereby potentially reducing seek activity for a given amount of data. Based on historic trends, analysts predict a future growth in HDD areal density (and therefore capacity) of about 40% per year.[84] Dell XPS 15 Battery
Dell XPS 17-L701X BatteryThe time to access data has not kept up with throughput increases, which themselves have not kept up with growth in storage capacity.
Seek time[edit source | editbeta] Dell XPS 15D Battery
Average seek time ranges from 3 ms[85] for high-end server drives, to 15 ms for mobile drives, with the most common mobile drives at about 12 ms[86] and the most common desktop type typically being around 9 ms. The first HDD had an average seek time of about 600 ms;[2] by the middle 1970s HDDs were available with seek times of about 25 ms.[87Dell XPS 15-L501X Battery
Dell XPS 17 Battery] Some early PC drives used a stepper motor to move the heads, and as a result had seek times as slow as 80–120 ms, but this was quickly improved by voice coil type actuation in the 1980s, reducing seek times to around 20 ms. Seek time has continued to improve slowly over time. Dell XPS 15-L502X Battery
Some desktop and laptop computer systems allow the user to make a tradeoff between seek performance and drive noise. Faster seek rates typically require more energy usage to quickly move the heads across the platter, Sony VGP-BPL13 Battery
causing louder noises from the pivot bearing and greater device vibrations as the heads are rapidly accelerated during the start of the seek motion and decelerated at the end of the seek motion. Quiet operation reduces movement speed and acceleration rates, but at a cost of reduced seek performance. Sony VGP-BPL14 Battery