Horace Dediu of Asymco charts the rise and fall of computing empires. He sees three distinct phases in the history of personal computing. The period from 1975 to 1991 was a time rapid growth but also a time of experiment with multiple standards jostling for preeminence. Between 1991 and 2007 Microsoft held a near monopoly, although one small alternative platform, Apple, did survive. The current third phase, starting with the emergence of the iPhone and iPad, has similarities to the first phase with multiple platforms fighting it out. Read the full report here.