Exploring Technologies !!: USB

Universal Serial Bus (USB) is developed in mid-1990's that defines the cables, connection and communication between computers and electronic devices.
USB was basically designed to standardize the connections of computer peripherals such as keyboards, pointing devices etc. and other electronic devices and PDAs

History

A group of seven companies began the development of USB in 1994: Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel.The goal was to make it fundamentally easier to connect external devices to PCs by replacing the multitude of connectors at the back of PCs, addressing the usability issues of existing interfaces, and simplifying software configuration of all devices connected to USB, as well as permitting greater data rates for external devices. A team including Ajay Bhatt worked on the standard at Intel. The first integrated circuits supporting USB were produced by Intel in 1995.

Versions

Prereleases

The USB standard evolved through several versions before its official release in 1996:

USB 0.7 – released in November 1994
USB 0.8 – released in December 1994
USB 0.9 – released in April 1995
USB 0.99 – released in August 1995
USB 1.0 Release Candidate – released in November 1995

Version	Release	Bandwith
USB 1.x	January 1996	1.5 Mbit/s (Low-Bandwidth) and 12 Mbit/s (Full-Bandwidth)
USB 2.0	April 2000	480 Mbit/s (effective throughput up to 35 MB/s or 280 Mbit/s)
USB 3.0	November 2008	5 Gbit/s and a usable data rate of up to 4 Gbit/s (500 MB/s)
USB 3.1	January 2013	10 Gbit/s, usable transfer speeds of only 7.2 Gbit/s, leading to a 30% encoding overhead.

Overview

In general, there are four basic kinds or sizes related to the USB connectors and types of established connections:

the older "standard" size, in its USB 1.1/2.0 and USB 3.0 variants (for example, on USB flash drives)
the "mini" size (primarily for the B connector end, such as on many cameras)
the "micro" size, in its USB 1.1/2.0 and USB 3.0 variants (for example, on most modern cellphones)
the versatile "USB On-The-Go" scheme, in both mini and micro sizes.

"A" & "B" connectors

The standard connectors were deliberately intended to enforce the directed topology of a USB network: type A connectors on host devices that supply power and type B connectors on target devices that receive power. This is intended to prevent users from accidentally connecting two USB power supplies to each other, which could lead to dangerously high currents, circuit failures, or even fire. USB does not support cyclic networks and the standard connectors from incompatible USB devices are themselves incompatible.

Standard connectors

Pin configuration of the USB connectors Standard A/B, viewed looking into face/end of plug

The USB 2.0 Standard-A type of USB plug is a flattened rectangle that inserts into a "downstream-port" receptacle on the USB host, or a hub, and carries both power and data. This plug is frequently seen on cables that are permanently attached to a device, such as one connecting a keyboard or mouse to the computer via USB connection.

USB connections eventually wear out as the connection loosens through repeated plugging and unplugging. The lifetime of a USB-A male connector is approximately 1,500 connect/disconnect cycles.

A Standard-B plug—which has a square shape with beveled exterior corners—typically plugs into an "upstream receptacle" on a device that uses a removable cable, e.g., a printer. On some devices, the Type B receptacle has no data connections, being used solely for accepting power from the upstream device. This two-connector-type scheme (A/B) prevents a user from accidentally creating an electrical loop.

Connectors types

Types of USB connectors left to right (ruler in centimeters): Micro-B plug, UC-E6 proprietary (non-USB) plug, Mini-B plug, Standard-A receptacle (upside down), Standard-A plug, Standard-B plug

There are several types of USB connectors, including some that have been added while the specification progressed. The original USB specification detailed Standard-A and Standard-B plugs and receptacles; the B connector was necessary so that cabling could be plug ended at both ends and still prevent users from connecting one computer receptacle to another. The first engineering change notice to the USB 2.0 specification added Mini-B plugs and receptacles.