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A Universal Serial Bus (USB) is a common interface that enables communication between devices and a host controller such as a personal computer (PC) or smartphone. It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives and flash drives. Because of its wide variety of uses, including support for electrical power, the USB has replaced a wide range of interfaces like the parallel and serial port.
A USB is intended to enhance plug-and-play and allow hot swapping. Plug-and-play enables the operating system (OS) to spontaneously configure and discover a new peripheral device without having to restart the computer. As well, hot swapping allows removal and replacement of a new peripheral without having to reboot.
There are several types of USB connectors. In the past the majority of USB cables were one of two types, type A and type B. The USB 2.0 standard is type A; it has a flat rectangle interface that inserts into a hub or USB host which transmits data and supplies power. A keyboard or mouse are common examples of a type A USB connector. A type B USB connector is square with slanted exterior corners. It is connected to an upstream port that uses a removable cable such as a printer. The type B connector also transmits data and supplies power. Some type B connectors do not have a data connection and are used only as a power connection.
Today, newer connectors have replaced old ones, such as the Mini-USB (or Mini-B), that has been abandoned in favor of the Micro-USB and USB-C cables. Micro-USB cables are usually used for charging and data transfer between smartphones, video game controllers, and some computer peripherals. Micro-USB are being slowly replaced by type-C connectors, which are becoming the new standard for Android smartphones and tablets.
A Universal Serial Bus (USB) is basically a newer port that is used as a common interface to connect several different types of devices such as:
It is designed for easy installation, faster transfer rates, higher quality cabling and hot-swapping. It has conclusively replaced the bulkier and slower serial and parallel ports.
The USB was co-invented and established by Ajay Bhatt, a computer architect who had been working for Intel. In 1994 seven companies that included Intel, Compaq, Microsoft, IBM, Digital Equipment Corporation (DEC), Nortel and NEC Corporation started the development of the USB.
Their objective was to make it easier to connect peripheral devices to a PC and eliminate the excessive amount of connectors. Factors involved included: creating larger bandwidths, streamlining software configurations and solving utilization problems for current interfaces.
The USB design is standardized by the USB Implementers Forum (USBIF) that is comprised of a group of companies supporting and promoting the USB. The USBIF not only markets the USB but maintains the specifications and upholds the compliance program. Specifications for the USB were created in 2005 with the 2.0 version. The standards were introduced by the USBIF in 2001; these included the older versions of 0.9, 1.0 and 1.1, which are backward compatible.
One of the greatest features of the USB is hot swapping. This feature allows a device to be removed or replaced without the past prerequisite of rebooting and interrupting the system. Older ports required that a PC be restarted when adding or removing a new device.
Rebooting allowed the device to be reconfigured and prevented electrostatic discharge (ESD), an unwanted electrical current capable of causing serious damage to sensitive electronic equipment such as integrated circuits.
Hot swapping is fault-tolerant, i.e. able to continue operating despite a hardware failure. However, care should be taken when hot-swapping certain devices such as a camera; damage can occur to the port, camera or other devices if a single pin is accidentally shorted.
Another USB feature is the use of direct current (DC). In fact, several devices use a USB power line to connect to DC current and do not transfer data. Example devices using a USB connector only for DC current include a set of speakers, an audio jack and power devices like a miniature refrigerator, coffee cup warmer or keyboard lamp.
USB Version 1 allowed for two speeds: 1.5 Mb/s (megabits per second) and 12 Mb/s, which work well for slow I/O devices. USB Version 2 allows up to 480 Mb/s and is backward compatible with slower USB devices. The first USB version 3 (USB 3.0 or SuperSpeed USB) was released in 2008, and allowed for a speed of 500 Mb/s. In 2013 and 2017, two new USB version 3 were released: USB 3.1 and USB 3.2, which allowed for 1.21 Gb/s and 2.42 Gb/s, respectively.