Editing USB flash drive (section)

==Technology==
{{Main|Flash memory|USB}}
[[File:MicroSDFDrive.JPG|thumb|A [[Kingston Technology|Kingston]] [[card reader]] which accepts [[SD card#microSD|MicroSD]] [[memory card]]s ([[Transcend Information|Transcend]] card shown partially inserted), and acts as a USB flash drive]]

On a USB flash drive, one end of the device is fitted with a single [[USB hardware#Connectors|USB plug]]; some flash drives additionally offer a [[micro USB]] plug, facilitating data transfers between different devices.

Inside the casing is a small printed circuit board, which has some power circuitry and a small number of [[Surface-mount technology|surface-mounted]] [[integrated circuit]]s (ICs).{{Citation needed|date=October 2018}} Typically, one of these ICs provides an interface between the USB connector and the onboard memory, while the other is the [[flash memory]]. Drives typically use the [[USB mass storage device class]] to communicate with the host.<ref>{{Cite web|url=https://www.premiumusb.com/blog/whats-inside-a-usb-drive|title=What's Inside a USB Drive?|website=PremiumUSB.com|access-date=2018-10-10|archive-date=2018-10-10|archive-url=https://web.archive.org/web/20181010213513/https://www.premiumusb.com/blog/whats-inside-a-usb-drive|url-status=live}}</ref>

=== Flash memory ===
Flash memory combines a number of older technologies, with lower cost, lower power consumption and small size made possible by advances in [[semiconductor device fabrication]] technology. The memory storage is 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 be re-written only after erasing the entire contents of the chip.

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, modifying 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.

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 microprocessor systems allowed this to be incorporated into extremely compact systems. Serial access requires far fewer electrical connections for the memory chips than [[Random-access memory|parallel access]], simplifying the manufacture of multi-[[gigabyte]] drives.

Computers access {{as of|2009|alt=modern}} flash memory systems very much like hard disk drives, where the [[Flash memory controller|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.

Many low-cost [[MP3 player]]s 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.

===Essential components===
[[File:Kingston DataTraveler flash drive disassembled.jpg|thumb|The internal mechanical and electronic parts of a Kingston 2&nbsp;GB flash drive]]

There are typically five parts to a flash drive:

* USB plug{{snd}} provides a physical interface to the host computer. Some USB flash drives use USB plug that does not protect the contacts, with the possibility of plugging it into the USB port in the wrong orientation, if the connector type is not symmetrical.
* USB mass storage controller{{snd}} a small [[microcontroller]] with a small amount of on-chip [[Read-only memory|ROM]] and [[Random Access Memory|RAM]].
* [[NAND flash]] memory chip(s){{snd}} stores data (NAND flash is typically also used in [[digital camera]]s).
* [[Crystal oscillator]]{{snd}} produces the device's main [[clock signal]] and controls the device's data output through a [[phase-locked loop]].
* Cover{{snd}} typically made of plastic or metal, protecting the electronics against mechanical stress and even possible short circuits.

===Additional components===
The typical device may also include:

[[File:USB flash drive2.jpg|thumb|The front and rear side of a USB flash drive with the casing removed]]

* [[Jumper (computing)|Jumpers]] and test pins – for testing during the flash drive's manufacturing or loading code into its [[microcontroller]].
* [[light-emitting diode|LEDs]] – indicate data transfers or data reads and writes.
* [[write protection|Write-protect]] switches – Enable or disable writing of data into memory.
* Unpopulated space – provides space to include a second memory chip. Having this second space allows the manufacturer to use a single printed circuit board for more than one storage size device.
* USB connector cover or cap – reduces the risk of damage, prevents the entry of dirt or other contaminants, and improves overall device appearance. Some flash drives use retractable USB connectors instead. Others have a swivel arrangement so that the connector can be protected without removing anything.
* Transport aid – the cap or the body often contains a hole suitable for connection to a [[key chain]] or [[lanyard]]. Connecting the cap, rather than the body, can allow the drive itself to be lost.
* Some drives offer expandable storage via an internal [[memory card]] slot, much like a memory [[card reader]].<ref>[http://www.ces-show.com/2006/review/pny/pny_usb_flash_drive.html PNY USB Flash Drive – CES 2006 – LetsGoDigital] {{Webarchive|url=https://web.archive.org/web/20090911085053/http://www.ces-show.com/2006/review/pny/pny_usb_flash_drive.html |date=2009-09-11 }}. Ces-show.com. Retrieved on 2011-05-18.</ref><ref>[http://www.techchee.com/2008/05/20/bluetrek-bizz-an-expandable-usb-drive-and-a-bluetooth-headset-in-one/ BlueTrek Bizz – an expandable USB  and a Bluetooth headset in one] {{Webarchive|url=https://web.archive.org/web/20140829094528/http://www.techchee.com/2008/05/20/bluetrek-bizz-an-expandable-usb-drive-and-a-bluetooth-headset-in-one/ |date=2014-08-29 }}. TechChee.com (2008-05-20). Retrieved on 2011-05-18.</ref>

===Size and style of packaging===
[[File:sushiusb.jpg|thumb|A particularly intricate [[novelty]] flash drive: Faux [[ikura]] [[Nigirizushi|gunkan-maki]]]]
[[File:Pendrive Shape of key.JPG|thumb|A [[skeuomorph]]ic flash drive in the shape of a [[key (lock)|key]]]]
[[File:Custom_USB_Drives.JPG|thumb|Assortment of USB flash drives]]

Most USB flash drives weigh less than {{cvt|1|oz|sigfig=1|order=flip}}.<ref>[http://peripherals.about.com/od/removablestorage/f/USBFAQ.htm Frequently Asked Questions About USB Flash Drives] {{Webarchive|url=https://web.archive.org/web/20090623102230/http://peripherals.about.com/od/removablestorage/f/USBFAQ.htm |date=2009-06-23 }}. Retrieved on 2011-05-18.</ref> While some manufacturers are competing for the smallest size,<ref>{{cite magazine|last=Newman |first=Jared |url=http://www.pcworld.com/article/2937161/worlds-smallest-128gb-usb-30-drive-pkparis-k1-picks-a-fight-with-sandisk-ultra-fit.html |title=World's smallest 128GB USB 3.0 drive: PKParis K'1 picks a fight with SanDisk Ultra Fit |magazine=[[PCWorld]] |date=2015-06-17 |access-date=2017-06-06}}</ref> with the biggest memory, offering drives only a few millimeters larger than the USB plug itself,<ref>{{cite web |last=Marino |first=Robert |url=http://www.computershopper.com/slideshow/guide-the-20-best-small-usb-flash-drives/sandisk-ultra-fit-usb-3.0-flash-drive |title=Guide: The 20 Best Small USB Flash Drives |website=Computershopper.com |date=2015-09-10 |access-date=2017-06-06 |archive-date=2017-06-07 |archive-url=https://web.archive.org/web/20170607010902/http://www.computershopper.com/slideshow/guide-the-20-best-small-usb-flash-drives/sandisk-ultra-fit-usb-3.0-flash-drive |url-status=live }}</ref> 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#CONNECTORS|USB port connectors]] on a computer housing are often closely spaced, plugging a flash drive into a USB port may block an adjacent port. Such devices may carry the USB logo only if sold with a separate extension cable. Such cables are USB-compatible but do not conform to the USB standard.<ref name=usb1>{{cite web |url=http://www.usb.org/developers/whitepapers/cablew~1.pdf |title=USB 1.0 Spec Position on Extension Cables and Pass-Through Monitors |publisher=Intel |date=1998-02-22 |access-date=2016-06-01 |url-status=dead |archive-url=https://web.archive.org/web/20160304121924/http://www.usb.org/developers/whitepapers/cablew~1.pdf |archive-date=2016-03-04 }}</ref><ref name=usb2>{{cite web|url=http://www.usb.org/developers/docs/ecn1.pdf|title=USB 2.0 Specification Engineering Change Notice (ECN) #1: Mini-B connector|access-date=1 June 2016|archive-url=https://web.archive.org/web/20150412121600/http://www.usb.org/developers/docs/ecn1.pdf|archive-date=2015-04-12|url-status=dead}}</ref>

USB flash drives have been integrated into other commonly carried items, such as watches, pens, laser pointers, and even the [[Swiss Army knives|Swiss Army Knife]]; others have been fitted with novelty cases such as toy cars or [[Lego]] bricks. USB flash drives with images of dragons, cats or aliens are very popular in Asia.<ref>[http://t3n.de/news/abgefahrene-usb-sticks-fernost-372900/ Bizarre USB flash drives from the Far East] {{Webarchive|url=https://web.archive.org/web/20120320213040/http://t3n.de/news/abgefahrene-usb-sticks-fernost-372900/ |date=2012-03-20 }} (German), t3n (2012-03-07). Retrieved on 2012-03-17.</ref> The small size, robustness and cheapness of USB flash drives make them an increasingly popular peripheral for [[case modding]].

===File system===
{{Main|Flash file system}}

Most flash drives ship preformatted with the [[FAT32]], or [[exFAT]] [[file system]]s. The [[Omnipresence|ubiquity]] of the FAT32 file system allows the drive to be accessed on virtually any host device with USB support. Also, standard FAT [[Disk checker|maintenance utilities]] (e.g., [[ScanDisk]]) can be used to repair or retrieve [[data corruption|corrupted data]]. However, because a flash drive appears as a USB-connected [[hard drive]] to the host system, the drive can be [[Disk formatting|reformatted]] to any file system supported by the host operating system.

====Defragmenting====
Flash drives can be [[defragmentation|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.<ref>[http://ask-leo.com/should_i_defragment_my_usb_flash_drive.html Should I defragment my USB Flash drive?] {{Webarchive|url=https://web.archive.org/web/20110707180424/http://ask-leo.com/should_i_defragment_my_usb_flash_drive.html |date=2011-07-07 }}. Ask-leo.com (2008-02-19). Retrieved on 2011-05-18.</ref> However, some sources claim<ref>{{cite web |url=http://www.wizcode.com/articles/comments/flash_memory_fragmentation_myths_and_facts/ |title=Flash Memory Fragmentation – Myths and Facts |website=Wizcode.com |access-date=2017-06-06 |archive-url=https://web.archive.org/web/20170614154251/http://www.wizcode.com/articles/comments/flash_memory_fragmentation_myths_and_facts/ |archive-date=2017-06-14 }}</ref> 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.

====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.<ref>{{cite web|url=http://www.micron.com/-/media/client/global/documents/products/technical-note/nand-flash/tn2942_nand_wear_leveling.pdf|title=TN-29-42: Wear-Leveling Techniques in NAND Flash Devices|access-date=24 January 2024|url-status=live|archive-url=https://web.archive.org/web/20231118153313/http://www.micron.com/-/media/client/global/documents/products/technical-note/nand-flash/tn2942_nand_wear_leveling.pdf|archive-date=18 November 2023}}</ref>

<!-- Note: Please don't add JFFS or YAFFS references to this article. While these two file systems, designed to minimize the inherent weaknesses of flash memory (e.g., memory wear), can be used on a flash drive, they provide no significant benefit. These filesystems are intended to assist with directly addressed flash memory (e.g. SmartMedia through a raw reader). A flash drive's memory layout is abstracted from the host system in the USB mass storage class, and the flash drive's controller chip performs tasks similar to those JFFS and YAFFS are intended for. -->

====Hard disk drive====
Sectors are 512 bytes long, for compatibility with hard disk 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 disk drives.

===Longevity===
The memory in flash drives was commonly engineered with [[multi-level cell]] (MLC) based memory that is good for around 3,000-5,000 program-erase cycles.<ref>{{cite web |url=http://www.anandtech.com/show/5734/kingston-hyperx-3k-240gb-ssd-review |title=Kingston HyperX 3K (240GB) SSD Review |publisher=Anandtec.com |date=2012-04-10 |access-date=2012-10-05 |archive-date=2013-01-13 |archive-url=https://web.archive.org/web/20130113163951/http://www.anandtech.com/show/5734/kingston-hyperx-3k-240gb-ssd-review |url-status=live }}</ref> Nowadays Triple-level Cell (TLC) is also often used, which has up to 500 write cycles per physical sector, while some high-end flash drives have [[single-level cell]] (SLC) based memory that is good for around 30,000 writes.<ref>{{Cite web|url=https://www.kingston.com/en/flashguide|title = Kingston's Flash Memory Guide - Kingston Technology}}</ref> 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. <!-- This may be wrong: some say SSDs, which use the same flash memory, lose their data after 12 months if left unpowered. <-- I've never seen or heard of that. -->

Estimation of flash memory endurance is a challenging subject that depends on the [[Single-level cell|SLC]]/[[Multi-level cell|MLC]]/[[Triple-level cell|TLC]] memory type, size of the flash memory chips, and actual usage pattern. As a result, a USB flash drive can last from a few days to several hundred years.<ref>{{cite web|url=http://blog.bowtiepromotions.com/2013/04/how-long-does-a-usb-flash-drive-last-part-ii/|title=How Long Does a USB Flash Drive Last? (Part II)|work=Promotional USB Flash Drives and Accessories|date=8 April 2013 |access-date=2015-03-21|archive-date=2015-04-02|archive-url=https://web.archive.org/web/20150402145935/http://blog.bowtiepromotions.com/2013/04/how-long-does-a-usb-flash-drive-last-part-ii/|url-status=live}}</ref>

Regardless of the endurance of the memory itself, the USB connector hardware is specified to withstand only around 1,500 insert-removal cycles.<ref>Blanchard, Richard (March 8th, 2007) [http://www.getusb.info/what-is-the-life-cycle-of-a-usb-flash-drive/ "What is the Life Cycle of a USB Flash Drive?"] {{Webarchive|url=https://web.archive.org/web/20130210065341/http://www.getusb.info/what-is-the-life-cycle-of-a-usb-flash-drive/ |date=2013-02-10 }}, GetUSB.info, retrieved June 14, 2010</ref>