Universal Serial Bus USB is an industry standard that establishes specifications for cables and connectors and protocols for connection, communication and power supply interfacing between computers, peripherals and other computers.
USB was designed to standardize the connection of peripherals to personal computers, both to communicate with and to supply electric power. It has largely replaced interfaces such as serial ports and parallel ports , and has become commonplace on a wide range of devices. Examples of peripherals that are connected via USB include computer keyboards and mice, video cameras, printers, portable media players, disk drives, and network adapters.
USB connectors have been increasingly replacing other types as charging cables of portable devices. This section is intended to allow fast identification of USB receptacles sockets on equipment. Further diagrams and discussion of plugs and receptacles can be found in the main article above. The Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices, when compared with previously existing standard or ad hoc proprietary interfaces.
The USB standard also provides multiple benefits for hardware manufacturers and software developers, specifically in the relative ease of implementation:. For a product developer, using USB requires the implementation of a complex protocol and implies an "intelligent" controller in the peripheral device. Developers of products that use the USB specification must sign an agreement with the Implementers Forum.
Use of the USB logos on the product requires annual fees and membership in the organization. Ajay Bhatt and his team worked on the standard at Intel; [10] [11] the first integrated circuits supporting USB were produced by Intel in Joseph C.
The original USB 1. The first widely used version of USB was 1. Apple Inc. The USB 2. The USB 3. As of [update] , approximately 6 billion USB ports and interfaces were in the global marketplace, and about 2 billion were being sold each year. Released in January , USB 1.
USB 1. Neither USB 1. Though many designs for a miniaturised type B connector appeared on many peripherals, conformity to the USB 1. There was no known miniature type A connector until USB 2.
USB 2. USB 3. SuperSpeed plugs and receptacles are identified with a distinct logo and blue inserts in standard format receptacles. The SuperSpeed bus provides for a transfer mode at a nominal rate of 5. Its efficiency is dependent on a number of factors including physical symbol encoding and link level overhead. Low-power and high-power devices remain operational with this standard, but devices using SuperSpeed can take advantage of increased available current of between mA and mA, respectively.
The first one preserves USB 3. The increase in bandwidth is a result of multi-lane operation over existing wires that were intended for flip-flop capabilities of the USB-C connector. Starting with the USB 3. USB4 is based on the Thunderbolt 3 protocol specification. Released in A USB system consists of a host with one or more downstream ports, and multiple Upstream And Downstream Questions Class 10 Zip peripherals, forming a tiered- star topology. Additional USB hubs may be included, allowing up to five tiers.
A USB host may have multiple controllers, each with one or more ports. Up to devices may be connected to a single host controller. The hub built into the host controller is called the root hub. A USB device may consist of several logical sub-devices that are referred to as device functions. A composite device may provide several functions, for example, a webcam video device function with a built-in microphone audio device function.
An alternative to this is a compound device , in which the host assigns each logical device a distinct address and all logical devices connect to a built-in hub that connects to the physical USB cable.
USB device communication is based on pipes logical channels. A pipe is a connection from the host controller to a logical entity within a device, called an endpoint. Because pipes correspond to endpoints, the terms are sometimes used interchangeably. Each USB device can have up to 32 endpoints 16 in and 16 out , though it is rare to have so many.
Endpoints are defined and numbered by the device during initialization the period after physical connection called "enumeration" and so are relatively permanent, whereas pipes may be opened and closed.
If the transfer is from the host to the endpoint, the host sends an OUT packet a specialization of a TOKEN packet with the desired device address and endpoint number. If the data transfer is from the device to the host, the host sends an IN packet instead. If the destination endpoint is a uni-directional endpoint whose manufacturer's designated direction Boat Upstream And Downstream Questions does not match the TOKEN packet e.
Otherwise, it is accepted and the data transaction can start. Endpoints are grouped into interfaces and each interface is associated with a single device function. An exception to this is endpoint zero, which is used for device configuration and is not associated with any interface. A single device function composed of independently controlled interfaces is called a composite device. A composite device only has a single device address because the host only assigns a device address to a function.
The enumeration starts by sending a reset signal to the USB device. The data rate of the USB device is determined during the reset signaling.
After reset, the USB device's information is read by the host and the device is assigned a unique 7-bit address. If the device is supported by the host, the device drivers needed for communicating with the device are loaded and the device is set to a configured state.
If the USB host is restarted, the enumeration process is repeated for all connected devices. The host controller directs traffic flow to devices, so no USB device can transfer any data on the bus without an explicit request from the host controller. In USB 2. High-speed USB 2. There may be one translator per hub or per port. Because there are two separate controllers in each USB 3.
Operating data rates for earlier devices are set in the legacy manner. This allows the host to load software modules for the device and to support new devices from different manufacturers. Device classes include: [49]. At first intended for magnetic and optical drives, it has been extended to support flash drives. It has also been extended to support a wide variety of novel devices as many systems can be controlled with the familiar metaphor of file manipulation within directories. The process of making a novel device look like a familiar device is also known as extension.
The ability to boot a write-locked SD card with a USB adapter is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium. Though most personal computers since early can boot from USB mass storage devices, USB is not intended as a primary bus for a computer's internal storage. However, USB has the advantage of allowing hot-swapping , making it useful for mobile peripherals, including drives of various kinds.
Several manufacturers offer external portable USB hard disk drives , or empty enclosures for disk drives. These offer performance comparable to internal drives, limited by the number and types of attached USB devices, and by the upper limit of the USB interface. Another use for USB mass storage devices is the portable execution of software applications such as web browsers and VoIP clients with no need to install them on the host computer.
Media Transfer Protocol MTP was designed by Microsoft to give higher-level access to a device's filesystem than USB mass storage, at the level of files rather than disk blocks. It also has optional DRM features. MTP was designed for use with portable media players , but it has since been adopted as the primary storage access protocol of the Android operating system from the version 4. The primary reason for this is that MTP does not require exclusive access to the storage device the way UMS does, alleviating potential problems should an Android program request the storage while it is attached to a computer.
The main drawback is that MTP is not as well supported outside of Windows operating systems. Joysticks, keypads, tablets and other human-interface devices HIDs are also progressively [ when? Device Firmware Upgrade DFU is a vendor- and device-independent mechanism for upgrading the firmware of USB devices with improved versions provided by their manufacturers, offering for example a way to deploy firmware bug fixes.
One consequence of this is that USB devices after being re-flashed may act as various unexpected device types. For example, a USB device that the seller intends to be just a flash drive can "spoof" an input device like a keyboard. See BadUSB. The USB Device Working Group has laid out specifications for audio streaming, and specific standards have been developed and implemented for Upstream And Downstream Problems Class 10 Reading audio class uses, such as microphones, speakers, headsets, telephones, musical instruments, etc.
The DWG has published three versions of audio device specifications: [59] [60] Audio 1. UAC 2. UAC 3. UAC 1. USB provides three isochronous fixed-bandwidth synchronization types, [70] all of which are used by audio devices: [71].
The connectors the USB committee specifies support a number of USB's underlying goals, and reflect lessons learned from the many connectors the computer industry has used. The female connector mounted on the host or device is called the receptacle , and the male connector attached to the cable is called the plug. By design, it is difficult to insert a USB plug into its receptacle incorrectly.
The USB specification requires that the cable plug and receptacle be marked so the user can recognize the proper orientation.
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