It's small, it's light and the important bit fits on a pair of spectacles. But it could be the ultimate in computer memory: as your mind begins to fail, a little chip could come to the rescue.

"You went out for some bread," it could remind you. "Turn here for the street where you live."

British Telecom engineers demonstrated a pioneer wearable computer system this week, which could, within two years, be helping people with Alzheimer's disease or other disabilities. It could serve as a walking mind.

The system uses the latest Pentium III laptop computer coupled to a pair of glasses. On one of the lens, a tiny screen close to the eye would show an image apparently the size of something on a desktop. Across the screen would scroll shopping lists, street directions, reminders of identity and family.

"We have developed a bodyworn computer system that can behave as a remembrance aid, accessing and delivering information when you most need it, based on where you are and what you are doing," said BT senior research scientist Mr Jerry Bowskill.

"Many people are already walking around with computers in the form of mobile phones. This is a step further.

"By using the glasses and a mouse strapped to the hand, all manner of information can be called up and be read on a head display."

Miniature computer screens have already begun to play a role in health. In the last three years, doctors have tested bionic chip-based systems to bridge spinal injury, helping paraplegics to stand, and even walk, by sending tiny pulses of electricity across severed nerves.

Electrode sensors have been used to "read" brainwaves and manipulate images on a computer screen. But several research groups are trying to widen the help that new technologies can give.

BT developed the prototype, but will not deliver the hardware. The system was developed with a US company called MicroOptical. What originally cost £8,000 sterling (€12,139) could ultimately go on the market for as little as £200.