USB flash drive

USB mass storage (English USB mass storage device, UMS ) are devices that communicate via the Universal Serial Bus (USB) and have a built-in data storage and are mainly used as a removable disk.

They find frequent use in the form of USB memory sticks, shortened and generalized also known as USB flash drives. Due to their higher storage capacity and access speed, as well as their ease of handling, they have displaced other mass storage application with similar profile as the floppy disk, the CD -RW and the Iomega Zip. The storage system is usually a flash memory.

The USB mass storage devices include all other mass storage devices, which are connected via USB to a computer, such as external hard drives, floppy drives and most MP3 players and digital cameras with built-in memory.

USB interface

USB mass storage is available for the USB 1.1 bus, the much faster USB 2.0 bus and the USB 3.0 bus with max. 625 MByte / s USB 2.0 -enabled mass storage can theoretically connected to a USB 2.0 port to transfer data at rates up to 480 Mbit / s ( 60 MByte / s) save and read, but, in practice, due to the amount of protocol overhead, rarely more than 30-35 MB / s. The USB 2.0 bus is backwards compatible with the USB 1.1 bus, but reduces the transmission rate of 12 Mbit / s (1.5 MB / s).

In 2008, the new specifications were introduced for the USB 3.0 interface. USB 3.0 mass storage devices are automatically recognized by most current operating systems; some older operating systems (eg Windows 98, XP) require the installation of a driver for the use of USB 3.0 mass storage devices. In 2013 are the storage capacities of USB 3.0 flash drives from a few MB and 1 TB. USB 3.0 has transmission mode " Super Speed" ( USB 2.0 distinguishable by the blue interface and the designation SS) with a transfer rate of up to 5 Gbit / s - more than ten times as fast as the fastest USB 2.0 data transfer rate of 480 Mbit / s Many newer USB 3.0 flash drives have minimum dimensions; some models are less than a 1 Euro coin. In October 2013, the French company PKparis launches the smallest claims to USB 3.0 flash drive in the world.

For USB devices, there is no lock, so that they can be disconnected from the computer at any time. This happen while data is being written to the device, it comes without warning to data loss. To prevent this, it should be notified to the operating system that the respective device to be removed. After completion of all write operations to the device outputs a message that the device can be removed now.

In the design of the parameters defined by USB standard plugs and jacks the problem of maintaining the power supply when removing the plug was taken into account by the two outer pins of the connector to which is applied the supply voltage, longer than the two middle, through which communication is settled.

Support by Operating Systems

Modern operating systems will recognize USB mass storage automatically. For older operating systems, whose development was completed before 2000, it may be necessary to install drivers before use. For operating systems that do not support USB, a USB device is generally only available if a driver was first installed for the bus.

The treatment of the USB mass storage is different from operating system to operating system: For Windows appears after plugging in a USB mass storage an additional drive, which the next available drive letter is assigned. In Mac OS USB stick as a drive ( "volume" ) is with his name on ( " mounted" ), he will be logged out for example by pulling on the trash. Under Linux, most USB mass storage devices are managed by the usb-storage kernel module, which integrates the USB mass storage device to the SCSI subsystem. USB mass storage device appear in Linux so usually as a SCSI device.

USB memory stick

Designations

The term USB (memory) stick it is not a German Scheinanglizismus, as is often supposed. The Eindeutschungen USB stick or USB memory stick are uncommon. (USB) Flash ( ROM) Drive refers to the technology in general and is not limited to pin-like devices. In English, USB flash drive is the most common name for a USB memory stick. Occasionally, the term USB memory stick is used, which is a registered trademark of Sony.

Technology

The USB memory stick is a passive disk in a compact housing. The data is electronically stored on a flash memory. The Israeli engineer, inventor and businessman Dov Moran is considered the inventor of the concept.

Recognized methods for testing the durability and robustness of USB flash drives do not exist. The saved data it will receive up to ten years according to the manufacturer. The memory cells of the sticks are affected by wear. They can be read while theoretically unlimited, but the manufacturers guarantee only 100,000 write cycles per memory cell. Therefore, the controller electronics ensures that frequently used memory locations, such as the FAT ( file allocation table ), physically come to lie on ever-changing areas. For mobile applications such as OpenOffice.org Portable write accesses are equally optimized.

The first sticks came in 2000 with a capacity of eight megabytes on the market. Meanwhile there are products with a capacity of up to 256 gigabytes with 240 MB / s read and 170 MB / s write speed ( March 2012) and 512 gigabyte (February 2013) - and also waterproof models. Since January 2014, a flash drive with a capacity of one terabyte is offered. Occasionally portable software is pre-installed, for example, for data encryption on the stick. The dimensions of USB flash drives are getting smaller. The smallest currently known stick is only 20 mm × 15 mm × 3 mm in size and has a weight of two grams (as of January 2012).

Interior: Flash memory chip (left) / controller chip (right)

Icon of a USB memory stick

Miniature version of an 8GB USB memory sticks ( 31 mm × 13 mm × 3.5 mm)

Defective 32GB USB flash drive Intenso High Speed ​​X-ray image

ReadyBoost

The Microsoft operating systems from version Windows Vista ReadyBoost bring a named function with that caches a small part of the disk on the stick to get around ( " caching " ), the long latency ( access time ) of the plate. Only in small and random data access, the stick is faster ( apart from a few high-performance USB 3.0 flash drives ), otherwise the access of the hard drive. Suitable only quick sticks. It is important here with the throughput especially the low latency when accessing. Tests revealed no significant speed advantages (see also Solid State Drive).

Wrong size information manipulated by controller chips

Since it is quite easy to report on manipulated controller chips incorrect size information on operating systems, it always comes back to cases where USB drives come with lower storage capacity than stated on the market. This can lead to loss of data, which are only noticed by the user when reading data.

Risks

The usage and data transfer via memory sticks can generally lead to security problems, for example, in companies, because their use is not subject to the inspection and maintenance by the system administrators. This does not just license and update mobile software problems, but also to exchange data with computers outside the company, thereby potentially malicious software can be introduced or data can be given from the company uncontrollably. In many companies, the use of mobile media is, therefore, prohibited or restricted to specific application domains. The United States Strategic Command has banned in November 2008, the use of personal USB flash drives and other portable storage media in their own computer network in order to protect it from another computer worm attacks. Many memory sticks can not be deleted reliable and may thus lead despite careful handling the unconscious release of data.

With USB sticks with supposedly safer, NIST - certified hardware encryption, the data could be decrypted in several cases by a simple attack method.

In the general public a USB flash drive is perceived as a storage medium like a floppy disk, "but in truth it is a computer speaking on a network to the host. The device can send all the data that it wants. " Against this background, USB sticks with case -specific behavior possible - special stealth mode, hack mode or auto delete when attempting to perform an unauthorized complete copy.

Combinations

Some USB mass storage combine several functions in one. The basic function is usually the mass memory, this is for example within a clock or a Swiss Army knife or is combined with an MP3 player, voice recorder, radio or digital camera.

Another use was the punk band WIZO, which published its stick -EP exclusively on a USB stick.

USB audio player (iPod shuffle ) on a 12 " Powerbook