If a digital device is connected to a personal computer, the chances are it will plug into a USB port. But what is USB, Who invented USB and how does it work?
What Is USB?
USB stands for Universal Serial Bus. It is a system for attaching peripherals to personal computers using standard physical connections and communication systems. USB allows for “hotplugging” devices (that is adding and removing devices with the power without having to switch the power off) and will also supply power to low consumption devices, negating the need for another power supply.
History of USB
USB has been released in 3 versions so far. Version 1.0 (January 1996) was the original release, but this was superseded by version 1.1 (September 1998) which was the first version to achieve mass adoption. These versions had a maximum data rate of 12Mbps (megabits per second).
USB Version 2.0 was released in April 2000 and is the current standard. This version has a maximum data rate of 480Mbps. All USB devices can be connected to a USB port on a PC, regardless of the version. However, the device will only be able to communicate with the PC at the rate of the slowest part of the connection.
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.
Connecting a Device to USB
The cable used to connect a USB device to a PC has 2 different connectors. One end has a flat USB ‘A’ connector that connects into the PC or a hub. The other end of the cable may have a standard USB ‘B’ connector or a mini or micro version of this, or if the manufacturer of the device wishes, the cable may have a connecter specific to the device.
A USB connector is difficult to connect incorrectly. USB connections only need a moderate force to insert or remove the connector, so it is easy to determine if an incorrect orientation is being attempted and no special tools are needed to add and remove device connections.
When a device is connected to a PC, the PC must determine what device has been connected and attempt to load a device driver for that device. If a device driver cannot be located, the PC will prompt the user for additional help on locating the device. Device drivers are usually found on a CD that comes with the device or can be downloaded from the manufacturer’s website.
A single USB controller (of which there may be more than one in a PC) can control up to 127 devices. However, having 127 USB ports on a PC would be physically very difficult to implement, as well as very expensive. In order to add more devices to a USB controller, a USB hub may be used. A hub is plugged into a USB socket and contains within itself 2 or more USB sockets into which other USB devices may be plugged.
It is also possible to plug another USB hub into the first one in order to further increase the number of ports. In fact, several hubs may be “daisy-chained” together to reach the maximum number of USB ports. Hubs may be powered and may also be used to power low consumption devices connected directly to them.
The Future of USB
A new version of USB, Version 3.0 has been proposed. This will transmit data at up to 4800Mbps on fibre optic cable that will run alongside the pair of copper cables used in current USB cable. The copper pair is included to allow backward compatibility with current USB devices and controllers.
Over the past few years, USB has become the de facto standard for connecting digital devices to a personal computer. With its mass adoption and faster upcoming versions, the future looks bright for USB.