Universal Serial Bus

Released in April of the millennium year, this connection has been part of a revolution in the way we connect items to our computers. Before USB, connecting was an unreliable process but coupled with the arrival of USB we had versions of Window that could support 'plug and play' which made the business of attaching things to your computer at least an order of magnitude simpler.

USB1 ran at 12Mbits per second, and they called it Hi-speed. So when USB followed with 480Mbits/sec they had to call it Full Speed and with the arrival of USB3 we now have Super Speed. Technologists should be more careful with our words.

Serial

It takes 8, 16, 32 or even 64 binary digits, or bits, to make up a computer word. If bits are sent one after another, as opposed to all at once, it is known as a serial connection. This is rather counter-intuitive: Wouldn't it be faster send whole words rather than a train of bits? Yes, but transferring words require those flat cables you find inside your computer.  And everything has to be synchronised which would be challenging if you are connecting different devices. So words are send one bit at a time and reassembled at the other end by the clever USB interface.

The clever thing about the USB design is that it manages to protect the tiny signals that pulse back and forward along the wire from interference in the noisy electronic environment in which they have to operate when plugged into a computer.

It achieves this by having two wires, called Data- and Data+, to carry each bit and the chip uses the difference (knows as differential signalling) in volts on these wires to determine if there is a bit or a zero. Using a pair of wires means that the interference in our electrically noisy environment on one wire will probably be the same on the other wire so the difference will be the same. 

Power

Another reason for the success of the USB was the provision of a power line in the plug. Suddenly, there was no need for a separate power pack and remember each one specific to the country's electrical regulations and plug configuration and needed a power socket on your desk.

The supply is only 500mA at 5V (is 2.5W max) but that will drive most bits of solid state equipment. This has been nearly doubled in the latest version of USB allowing connected equipment to draw up to 4.5W

Flexible USB

USB is smart so it can cope with a mouse, which does not transfer much data but can't be kept waiting (in technical terms need low 'latency') because you want to see the pointer move immediately. Your data storage on the other hand, needs maximum transfer speed but can wait a few micro moments for other traffic without affecting performance.

Display devices also their own, special needs, if you are to see a steady picture. These have a fixed as well as a predictable data load and USB can allocate a pipe for the data that suits the needs of these different type of device.

USB3

The latest incarnation (2010) has the technology to support transfer rates of 4.8Gbits/sec, a mere 10 times faster than its predecessor. The plugs will look the same but they part of the plug, as well as the socket, will be blue.

Although the plugs look alike, the USB3 has some extra pins recessed so that you cannot see them. This clever design feature will enable users to evolve to the new system without too much frustration with all existing equipment becoming redundant when a new computer is purchased.

USB-v-RS232

Anybody over 30 will remember that the bulky RS232 plug used to be the standard for serial connections. This is still the plug you will find on serious communications equipment as it allows for two-way communication. There are very few domestic or office uses where such sophistication is necessary. (USB is known as a half-duplex system as only one end can send data while the other end receives it.)

And on the subject of terminology, where does the 'B' or Bus part of the system come from? Well that is another throwback to former times when 'bus bars' were a feature of most electrical and electronic systems. A busbar is a heavy conductor, often made of a bar of copper to interconnect and distribute electric currents but has evolved to mean a circuits that connects the CPU with other devices in a computer. So a computer has a power bus and probably several different data buses.

 ©WritersServices.com 2000-2011