Från Wikipediaartikel på South Park:
When the show began using computers, the cardboard cutouts were scanned and re-drawn with CorelDRAW, then imported into PowerAnimator, which was used with SGI workstations to animate the characters. The workstations were linked to a 54-processor render farm that could render 10 to 15 shots an hour.
Beginning with season five, the animators began using Maya instead of PowerAnimator. The studio now runs a 120-processor render farm that can produce 30 or more shots an hour.