Universal Serial Bus

Universal Serial Bus
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Name	Universal Serial Bus
Caption	The USB-IF logo
Type	Bus
Designer	Ajay Bhatt, Intel, Compaq, Microsoft, DEC, IBM, Nortel
Design date	1996
Manufacturer	Various
Production date	Since May 1996
Superseded	Serial port, Parallel port, Game port, Apple Desktop Bus
Superseded-by	USB4
Length	Varies by cable
Width	Varies by connector
Height	Varies by connector
Connector	Various
Data signal	Differential serial
Data bandwidth	1.5 Mbit/s to 80 Gbit/s
Numdev	127 per host controller
Protocol	Serial

Universal Serial Bus. It is an industry standard for cables, connectors, and communication protocols that establishes a connection, communication, and power supply between computers and peripheral devices. Developed to simplify and standardize connections to personal computer hosts, it has largely replaced earlier interfaces like the serial port and parallel port. The standard is maintained by the USB Implementers Forum.

Overview

The development of this interface was driven by a consortium of companies including Intel, Compaq, Microsoft, and DEC, with key contributions from engineers like Ajay Bhatt. Its primary goal was to create a single, standardized, and easy-to-use connector to replace the multitude of proprietary interfaces common in the 1990s, thereby enhancing the user experience with plug and play and hot swapping capabilities. It has become ubiquitous, used for connecting a vast array of devices from keyboards and mouses to external hard drives and smartphones, fundamentally shaping modern consumer electronics. The specification's governance and certification are managed by the USB Implementers Forum, which ensures compatibility across devices from different manufacturers like Apple, Samsung, and Dell.

Technical specifications

The architecture is based on a tiered-star topology, with a single host controller managing communication with all connected devices, supporting up to 127 peripherals through the use of hubs. Data is transmitted using a differential signaling method over a twisted-pair data cable to reduce noise, with communication following a strict packet switching protocol initiated by the host. The electrical specifications define voltage levels, with standard downstream ports supplying 5 volts, and include detailed timing requirements for signal integrity. Key to its operation are defined data transfer types—Control, Interrupt, Bulk, and Isochronous—each serving different needs from device configuration to streaming audio.

Connector types

The original standard connectors were the rectangular USB-A for hosts and the square USB-B for peripherals, which became common on printers and scanners. Smaller connectors were later introduced for portable devices, including the Mini-USB and Micro-USB connectors, the latter being mandated for charging by the European Union. The reversible USB-C connector, developed by the USB Implementers Forum, is the modern standard, featuring a symmetrical design and supporting advanced protocols like USB4 and Thunderbolt. Various other proprietary and standard connectors exist, such as the Apple-specific Lightning connector, though the industry is consolidating around USB-C.

Version history

The initial release, USB 1.0, in 1996 offered speeds of 1.5 Mbit/s, with the widespread USB 1.1 clarifying specifications. A major leap came with USB 2.0, also called "Hi-Speed," increasing the data rate to 480 Mbit/s and becoming the baseline for decades. USB 3.0 (marketed as "SuperSpeed") introduced a new physical bus and significantly faster 5 Gbit/s transfer rates, with subsequent enhancements like USB 3.1 and USB 3.2 doubling and quadrupling that speed. The latest standards, USB4 and USB4 2.0, leverage the Thunderbolt protocol from Intel to provide speeds up to 80 Gbit/s and mandatory use of the USB-C connector.

Device classes

The specification defines numerous device classes to provide standard drivers, with the most common being the USB human interface device class for keyboards, mouses, and joysticks. The USB mass storage device class enables portable storage like flash drives and external hard drives to appear as drives to operating systems like Microsoft Windows and macOS. Audio and video functions are handled by the USB audio device class and USB video device class, supporting devices like webcams and microphones. Other important classes include the USB communications device class for modems and the USB power delivery specification for advanced charging.

Power delivery

Beyond data, the interface provides bus power, initially supplying up to 2.5 watts, which was sufficient for devices like mouses and flash drives. The USB Battery Charging specification increased available current for charging devices like the iPhone and Samsung Galaxy phones. The advanced USB Power Delivery specification, developed in conjunction with the USB Implementers Forum, supports negotiating much higher power levels—up to 240 watts—enabling fast charging for laptops and monitors. This capability, combined with features like power negotiation, has made it a universal charging standard, influencing regulations from the European Union and adoption by companies like Google and Apple. Category:Computer hardware Category:Computer buses Category:1996 introductions