p.s. Extraordinarily gifted and organized students at CMU were referred to be "on the 4 year plan". Interestingly, some of the most speedy completers of their PhD work were among the least well prepared for the MSc coursework - there was very little correlation between people who blitzed tons of coursework fast with high grade (the 'hares', like me) and the 'tortoises' - who seemed to struggle with the breadth requirements but had solid research ideas that they plugged away on from Day 1. So a woman who didn't have a formal CS background and completed her MSc requirements slowly was the first person to get a PhD in our year.