From The Stargate Omnipedia
A computer network allowing users immediate access to the sum total of their civilization's knowledge and wisdom, the Link was a prominent piece of technology within the Bio-dome
. Linked directly to the brain of every individual within the dome, it was capable of delivering needed information almost instantaneously and, unbeknownst to the population, also capable of erasing memories just as easily. Children were also able to learn by accessing lessons through the Link instead of attending school.
The super-computer accessed by the Link also managed the bio-dome in which it functioned, monitoring atmospheric analysis, dome integrity, power utilization and coolant pressure. The link has been directly responsible for controlling the dome's size and the size of the town's population, shrinking both in order to maintain the survival of the whole when its power supply began to diminish. Simply doing what is was programmed to do, it was capable of performing its job all too well.
Thousands of texts were on file and accessible by the Link to the townspeople, including detailed information about the world prior to the Link's existence -- including the whereabouts of the Stargate and who controlled the planet. However, very little of this information was reliable, as the Link was capable of altering vast amounts of data, even erasing the town's memories of people.
The Link communicated with the population via Link nodes, removable, U-shaped devices worn on the left temple. When the Link reset information and altered their memories, lines of streaming code would process across the display monitors, though no one connected to the link would notice because they were receiving the updated information and were momentarily "deactivated," in a sense.
Samantha Carter and Pallan managed to free the town from the Link, and SG-1 relocated the people to a new world before the bio-dome collapsed entirely.
Revisions - SG-1 frees the inhabitants of P3X-289 from the Link, which is rewriting their memories and systematically sending them to their deaths. The Link is left behind when the people are relocated to another world.