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Computerworld - Without some good means of input and output, a computer makes a pretty good doorstop or boat anchor. Once we start plugging things into a computer, however, it can receive data and instructions, control other machines, and produce text and images on paper or on a screen. But "plugging in" implies the existence of sockets, jacks or other types of fittings into which something can be connected.

Though it seems like such a simple idea, plugging in calls for standards of compatibility and interoperability, both mechanical (will it fit?) and electrical (will it work?). For example, consider the lowly electrical outlet in the wall. It has two or three prong holes in a standard arrangement, and in the U.S. we can expect it to provide 110 volts of 60-Hz alternating current electrical power. Go to the U.K., and you find incompatible plugs and outlets delivering 220 volts that can fry your American appliances.

Computers aggravate this problem because they use a multitude of different connectors - and sometimes use the same type of connector for entirely different devices.

As technology has advanced, older connectors often couldn't handle the newer, higher-density signals, and replacements had to be created. Thus the number of different connectors grew, until the industry realized that it had to simplify things.

The standard USB B and A connectors work with most modern peripherals.

The Universal Serial Bus (USB) idea was launched by Intel Corp. with the goal of replacing virtually all other connectors except for video. It was then taken up by many other companies, and in 1995 the USB 1.0 standard was announced. In 1997, a Portland, Ore.-based organization called USB Implementers Forum Inc. was created to coordinate USB development and standards.

USB developers also took the opportunity of the clean, new design to add a significant new capability: USB connectors and cables can deliver not only data to an attached peripheral, but power as well, thus eliminating the need for (and the cost of) those bricklike power-supply transformers that come with so many peripherals.

Today, most desktop computers and laptops have at least two USB ports, and they may or may not have the older legacy connections.

With USB, you can often connect one device to another in a daisy-chain fashion. Thus a mouse can connect to a keyboard instead of plugging into the back of the computer. And that keyboard can connect to a USB port in the monitor. If you need more USB ports, just connect a hub and get three to seven more ports. In theory, at least, up to 127 USB devices can be interconnected.