Computer scientists from around the world will gather in Boston this week at Computer-Human Interaction 2009 to discuss the latest developments in computer interfaces. To coincide with the event, we present a roundup of the coolest computer interfaces past, present, and future.

The Command Line
The granddaddy of all computer interfaces is the command line, which surfaced as a more effective way to control computers in the 1950s. Previously, commands had to be fed into a computer in batches, usually via a punch card or paper tape. Teletype machines, which were normally used for telegraph transmissions, were adapted as a way for users to change commands partway through a process, and receive feedback from a computer in near real time.

Video display units allowed command line information to be displayed more rapidly. The VT100, a video terminal released by Digital Equipment Corporation (DEC) in 1978, is still emulated by some modern operating systems as a way to display the command line.

Graphical user interfaces, which emerged commercially in the 1980s, made computers much easier for most people to use, but the command line still offers substantial power and flexibility for expert users.

The Mouse
Nowadays, it's hard to imagine a desktop computer without its iconic sidekick: the mouse.

Developed 41 years ago by Douglas Engelbart at the Stanford Research Institute, in California, the mouse is inextricably linked to the development of the modern computer and also played a crucial role in the rise of the graphic user interface. Engelbart demonstrated the mouse, along with several other key innovations, including hypertext and shared-screen collaboration, at an event in San Francisco in 1968.

Early computer mouses came in a variety of shapes and forms, many of which would be almost unrecognizable today. However, by the time mouses became commercially available in the 1980s, the mold was set. Three decades on and despite a few modifications (including the loss of its tail), the mouse remains relatively unchanged. That's not to say that companies haven't tried adding all manner of enhancements, including a mini joystick and an air ventilator to keep your hand sweat-free and cool.

Logitech alone has now sold more than a billion of these devices, but some believe that the mouse is on its last legs. The rise of other, more intuitive interfaces may finally loosen the mouse's grip on us.

The Touchpad
Despite stiff competition from track balls and button joysticks, the touchpad has emerged as the most popular interface for laptop computers.

With most touchpads, a user's finger is sensed by detecting disruptions to an electric field caused by the finger's natural capacitance. It's a principle that was employed as far back as 1953 by Canadian pioneer of electronic music Hugh Le Caine, to control the timbre of the sounds produced by his early synthesizer, dubbed the Sackbut.

The touchpad is also important as a precursor to the touch-screen interface. And many touchpads now feature multitouch capabilities, expanding the range of possible uses. The first multitouch touchpad for a computer was demonstrated back in 1984, by Bill Buxton, then a professor of computer design and interaction at the University of Toronto and now also principle researcher at Microsoft.

The Multitouch Screen
Mention touch screen computers, and most people will think of Apple's iPhone or Microsoft's Surface. In truth, the technology is already a quarter of a century old, having debuted in the HP-150 computer in 1983. Long before desktop computers became common, basic touch screens were used in ATMs to allow customers, who were largely computer illiterate, to use computers without much training.

However, it's fair to say that Apple's iPhone has helped revive the potential of the approach with its multitouch screen. Several cell-phone manufacturers now offer multitouch devices, and both Windows 7 and future versions of Apple's Macbook are expected to do the same. Various techniques can enable multitouch screens: capacitive sensing, infrared, surface acoustic waves, and, more recently, pressure sensing.

With this renaissance, we can expect a whole new lexicon of gestures designed to make it easier to manipulate data and call up commands. In fact, one challenge may be finding means to reproduce existing commands in an intuitive way, says August de los Reyes, a user-experience researcher who works on Microsoft's Surface.