A USB stick is a small removable media that connects to the port Universal Serial Bus to a computeror, more recently, some
Hi-Fi, DVD players lounge, car radios, boom boxes,televisions, etc.. USB key contains a flash memory and thus has no mechanical element,
which makes it very resistant to shocks. There are variants containing a small hard drive instead of flash memory, but in this case we will not use the term memory stick but microdrive or external hard drive.
Description and operation
USB drives are powered via the USB port on which they are connected. They are insensitive to dust and scratches, unlike floppy disks, to CD or DVD,
which is an advantage in terms of reliability. In 2008, the keys are marketed as USB 2.0 format. USB drives are relatively standardized
, however some are not compatible with certain operating systems, requiring theinstallation of a driver[ref. needed].
The USB display capabilities ranging from a few MB to 256 GB (2010) and some are smaller than 1 euro coin.
The USB-based mini hard drives (see Microdrive) have a flow generally better than the USB flash drive[ref. necessary],
but access times are longer. They are also somewhat more fragile and can become hot when used intensively. In addition, their size is slightly larger but they still hold easily in your pocket.
The USB has several features, detailed below.
The lifetime (or MTTF) of the key itself is not specified and may fail after a few months as a few years, leading to partial or total loss of data.
Manufacturers announce data retention for at least ten yearsor more1. Computerworld is more reserved and draws attention to the differences
significant different between models2 in his article Not all USB drives are Created Equal. This term comes from the fact that the electric charge which is stored information
is not completely isolated and may disappear after a while, before which to perform a rewrite to ensure data retention3
And the quality of the insulation will therefore define the retention time.
Do not confuse this retention time with the lifetime of the key, which can break down or lose data before it.
Data loss can then be caused by:
- limited data retention, due to the flash memory ;
- a breakdown of the key, like any other material;
- a software problem in operating system;
- error handling software from the user;
- an error of material handling and is not indestructible, although more resistant than other storage media.
Performance depends heavily on the model design, including choice of components, architecture and memory controller. Techniques such as amplification of writing affect the performance4.
They may also vary depending on the operating system or hardware on which it is used.
The data rate varies in reading, writing and also depends on the number of files copied and content organization of the key.
can have speeds of several Mbps to several tens of Mb / s, which can
fall in the case of transfer of a large number of small files.
Different criteria improve the ergonomics of the key: the presence and positioning of light activity, protected Connector
(Rotary cap or retractable, retractable connector) accessories (strap, chain or cord necklace-keychain, USB extension cable)
portable software (depending on encryption, data synchronization, import mails or suite), shell design, etc..5.
With Windows Vista ReadyBoost certification appeared describing a USB key that can alleviate the burden on the hard drive at the launch of a PC.
The USB 2.0 has a speed slower than a hard disk 2009, but his time latencyaccess to every file of a few ms
is better than a few tens of ms hard drive. The balance of the key can be positive.
Certain keys have different functions, or an additional function of the memory function of mass:
- an integrated fingerprint reader for biometric authentication of the holder of the USB6 ;
- a reader capable of restoring the files they contain music, including format MP3, thus becoming music players
- miniatures (the key with one AAA battery and a headset weighs 60 grams);
- a tuner for FM radio, possibly with the option to save the stream in the embedded memory, or digital terrestrial television.
- In the latter case, it is necessary to connect an antenna to the key;
- a microphone, he captures the sounds being recorded in the memory. The key then acts dictaphone ;
- SIM card reader;
- a modem for accessing data to a mobile phone network (3G key "). In this case the key features a mobile telephone terminal and a SIM card;
- Interface IrDA for communication with mobile devices.
There are also some USB Swiss Army knives.
A key may be a public partition and access to which is subject to a password. The confidential data is secure (connection parameters,
Portfolio passwords, email, etc.)..
OS Compatibility 
If the firmware allows, some computers have the opportunity to start a Live Distribution, that is to say an operating system executable from removable media,
from a USB key. Microsoft does not offer on its operating systems.
When the firmware does not allow it to circumvent the problem by booting from a CD-ROM containing drivers for USB in turn to emulation
starting on the key (see eg Flonix). This manipulation is possible with a BIOS or EFI, and not with an Open Firmware.
Inside (64 MB)
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- A male USB connector (type A).
- A controller Bear Technology Inc.. OTi-2168 USB 2.0.
This circuit implements the controller for USB 2.0 and provides an
interface between data transmitted linearly and the block structure of
the flash memory. It avoids the low-level management of memory and contains a small microcontroller RISC and a little RAM and ROM. The data is transmitted to Hynix (no4) via a bus data / address on 8 lines.
- JP1 and JP2 two connectors with 10 pins, mainly for testing and debugging.
- Hynix Semiconductor HY27USxx121M, flash memory , which contains 4,096 independent blocks (each with 16 kilobytes) or 64 megabytes in total.
- An oscillator quartz SKC Shin Chang Electronics clocked at 12 MHz.
- An LED to indicate activity of the key.
- A switch with two positions to protect the key in writing.
blank area ready to receive another flash memory to provide a model
with 128 megabytes without having to create another schema.
Comparison with other mass storage devices 
The disks are hardly used since 2006, because of their low capacity (1.44 MB), their slow and especially their inconstancy.
The disks were long the most popular external storage of files, but their readers n'équipent most standard computers since 2005.
PCs have a USB interface, however, since they are defined as such by the annual specifications developed jointly by Microsoft and Intel.
USB drives are faster than floppies, contain more data and do not require any special driver.
Floppy disks are still an option for their ease of use with older operating systems
(Like Windows 98 SE, which requires the installation of a driver using a USB key) and ease of starting.
The USB management is extremely complex, and thus relatively large in lines of code. Accordingly, it is not yet present in every BIOS.
USB and software
Some USB keys come with the software format U3 created at the initiative of a group of key manufacturers including SanDisk and M-Systems:
connecting the key shows under Windows, a storage device read-write, which appears as a disk drive and a read-only device,
which appears as an optical device. U3 smart drives contain an embedded cryptographic processor. This solution implies the acceptance in consideration of a security risk,
depending on the degree of confidence that gives the manufacturer.
The increase in capacity of USB keys can install the software and move around with its data and software preferred. With the BIOS current (2008),
you can even boot a complete system from a USB.
Some Web sites begin to offer "prebuilt packages" of commercial software or free license version installable on a USB key.
It is common to install a Linux distribution on a USB key. Just extract the ISO from a Live CD on this key and make it bootable (see Live USB).
In contrast, the number of writes on a USB key is technically limited
(10 000 to 100 000 by the production technology of the cells),
should take several precautions if you want to use read-write7 (do not place any swap file swap).
Virus and USB
A new type of security threat has emerged in 2007 in London, where malicious people have deliberately left USB sticks lying around
containing Trojansin order to infect the computers of those who picked
History capacity USB sticks
|256 GB||July 200910||Kingston||DataTraveler 300|
|128 GB||June 2009||Kingston||DataTraveler 200|
|32 GB||2008||Netac Technology11||OnlyDisk ™|
|16 GB||2007 (" first ultra-high ")||Netac Technology||OnlyDisk ™|
|1 GB||2001||Netac Technology||OnlyDisk ™|