This is by Jack L. Chalker, the Soul Rider series, also known as the Flux and Anchor series. Most of the action took place in "wild" areas, where stabilization fields didn't hold sway and anyone sufficiently in touch with the computers that maintained reality could do what appeared, to the powerless, as magic.
From the blurb of the first volume:
Cassie did not feel the soul rider enter her body...but suddenly she knew that Anchor was corrupt, and that, far from being a formless void from which could issue only mutant changelings and evil wizards, Flux was the source of Anchor's very existence.
The price of her new knowledge is exile, yet Cassie and the Rider of her soul are the only hope for the redemption of both Flux and Anchor.
