USB

USB. The Universal Serial Bus is an industry standard for cables, connectors, and communication protocols used for connection, communication, and power supply between computers and electronic devices. Developed in the mid-1990s, it was designed to standardize the connection of peripherals to personal computers, replacing a multitude of earlier interfaces. Its widespread adoption has made it a ubiquitous feature on devices ranging from desktop computers and smartphones to game consoles and industrial equipment.

Overview

The primary goal was to simplify the connection of external peripherals, eliminating the need for separate expansion cards and confusing configurations associated with legacy ports like the RS-232 serial interface. A key innovation was its support for hot swapping, allowing devices to be connected and disconnected without rebooting the host system. The standard is maintained by the USB Implementers Forum, a consortium of industry leaders including Intel, Microsoft, Apple Inc., and Hewlett-Packard. Beyond data transfer, it also provides a standardized power bus, enabling the charging of devices and powering of peripherals like external hard drives.

Technical specifications

The architecture is based on a tiered-star topology, with a single host controller managing the entire bus. Communication is packet-based, utilizing a protocol where the host initiates all data transactions. Electrical specifications define power delivery, with initial versions supplying up to 2.5 watts, while modern implementations like USB Power Delivery can deliver over 100 watts. Data transfer modes include low-speed, full-speed, high-speed, and super-speed, with theoretical maximums evolving from 1.5 Mbit/s in the original specification to 40 Gbit/s in the latest generations. The system uses NRZI encoding for data on the wire.

Connector types

A variety of connector shapes have been standardized to serve different device form factors and capabilities. The classic USB Type-A connector, rectangular in shape, is found on most host controllers like those in Dell computers. The smaller USB Type-B and its variants, such as the square USB-B, were common on peripherals like Epson printers. The reversible USB-C connector, developed by the USB Implementers Forum, is now the modern standard for both hosts and devices, supporting the highest data and power rates. Other legacy types include the Mini-USB and Micro-USB connectors, once prevalent on portable devices from manufacturers like Samsung.

Development and adoption

Development began in 1994 by a core group of companies including Intel, Compaq, and IBM, with engineer Ajay Bhatt as a chief architect. The first official specification, USB 1.0, was released in January 1996. Widespread adoption was catalyzed by its inclusion as a mandatory interface in the PC 97 design guide by Microsoft and its native support in the Windows 98 operating system. The introduction of the iMac G3 by Apple Inc. in 1998, which used USB ports exclusively, was a landmark event in popularizing the standard. Later, its use for charging mobile phones, solidified by the European Union's common charger initiative, cemented its global ubiquity.

Variants and versions

The main version progression includes USB 1.1, USB 2.0 (offering higher-speed data transfer), USB 3.0 (introducing super-speed), and USB4, which incorporates the Thunderbolt protocol from Intel. Specialized variants have been created for specific applications. USB On-The-Go allows devices like Android phones to act as a host. USB Battery Charging specification increased available current for charging. USB Power Delivery is a separate protocol for advanced power negotiation. Other form-factor variants include Lightning, a proprietary connector from Apple Inc., and DisplayPort Alternate Mode, which allows USB-C cables to carry video signals to monitors from Lenovo laptops.

Category:Computer hardware Category:Computer buses Category:1996 introductions