48. Manes and Andrews, Gates, 1564.

49. “Bill Gates to Sign Off at Microsoft,” AFP, June 28, 2008.

50. William H. Gates and Christos P. Papadimitriou, “Bounds for Sorting by Prefix Reversal,” Discrete Mathematics, 1979; Harry Lewis, “Reinventing the Classroom,” Harvard Magazine, Sept. 2012; David Kestenbaum, “Before Microsoft, Gates Solved a Pancake Problem,” NPR, July 4, 2008.

51. Allen, Idea Man, 62.

52. Author’s interview with Bill Gates.

53. Allen, Idea Man, 1058.

54. Author’s interview with Bill Gates.

55. Bill Gates and Paul Allen to Ed Roberts, Jan. 2, 1975; Manes and Andrews, Gates, 1810.

56. Allen, Idea Man, 160.

57. Allen, Idea Man, 1103.

58. Manes and Andrews, Gates, 1874.

59. Author’s interview with Bill Gates; Allen, Idea Man, 1117.

60. Wallace and Erickson, Hard Drive, 76.

61. Allen, Idea Man, 1163.

62. Allen, Idea Man, 1204.

63. Allen, Idea Man, 1223; Wallace and Erickson, Hard Drive, 81.

64. Author’s interview with Bill Gates.

65. Remarks of Bill Gates, Harvard Gazette, June 7, 2007.

66. Author’s interview with Bill Gates.

67. The section on Gates in Albuquerque draws on Allen, Idea Man, 1214 and passim; Manes and Andrews, Gates, 2011 and passim; Wallace and Erickson, Hard Drive, 85 and passim.

68. Bill Gates oral history, Henry Ford Innovation Series.

69. Allen, Idea Man, 1513.

70. Author’s interview with Bill Gates.

71. Allen, Idea Man, 1465; Manes and Andrews, Gates, 2975; Wallace and Erickson, Hard Drive, 130.

72. Author’s interview with Bill Gates.

73. Allen, Idea Man, 1376.

74. Fred Moore, “It’s a Hobby,” Homebrew Computer Club newsletter, June 7, 1975.

75. John Markoff, What the Dormouse Said (Viking, 2005; locations refer to the Kindle edition), 4633; Steven Levy, Hackers (Anchor/Doubleday, 1984; locations refer to the twenty-fifth anniversary reissue, O’Reilly, 2010), 231.

76. Author’s interview with Lee Felsenstein; Lee Felsenstein oral history, by Kip Crosby, Computer History Museum, May 7, 2008.

77. Homebrew Computer Club newsletter, Feb. 3, 1976, http://www.digibarn.com/collections/newsletters/homebrew/V2_01/gatesletter.html.

78. Author’s interview with Bill Gates.

79. Harold Singer, “Open Letter to Ed Roberts,” Micro-8 Computer User Group newsletter, Mar. 28, 1976.

80. Author’s interview with Lee Felsenstein.

81. Bill Gates interview, Playboy, July 1994.

82. This section draws from my Steve Jobs (Simon & Schuster, 2011), which was based on interviews with Steve Jobs, Steve Wozniak, Nolan Bushnell, Al Alcorn, and others. The Jobs biography includes a bibliography and source notes. For this book, I reinterviewed Bushnell, Alcorn, and Wozniak. This section also draws on Steve Wozniak, iWoz (Norton, 1984); Steve Wozniak, “Homebrew and How the Apple Came to Be,” http://www.atariarchives.org/deli/homebrew_and_how_the_apple.php.

83. When I posted an early draft of parts of this book for crowdsourced comments and corrections on Medium, Dan Bricklin offered useful suggestions. We got into an exchange about the creation of VisiCalc, and I subsequently added this section to the book. It is partly based on email exchanges with Bricklin and Bob Frankston and on chapter 12, “VisiCalc,” in Dan Bricklin, Bricklin on Technology (Wiley, 2009).

84. Email from Dan Bricklin to the author; Dan Bricklin, “The Idea,” http://www.bricklin.com/history/saiidea.htm.

85. Peter Ruell, “A Vision of Computing’s Future,” Harvard Gazette, Mar. 22, 2012.

86. Bob Frankston, “Implementing VisiCalc,” unpublished, Apr. 6, 2002.

87. Frankston, “Implementing VisiCalc.”

88. Author’s interview with Steve Jobs.

89. IBM corporate history, “The Birth of the IBM PC,” http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_birth.html.

90. Manes and Andrews, Gates, 3629.

91. Manes and Andrews, Gates, 3642; Steve Ballmer interview, “Triumph of the Nerds,” part II, PBS, June 1996. See also James Chposky and Ted Leonsis, Blue Magic (Facts on File, 1988), chapter 9.

92. Bill Gates and Paul Allen interview, by Brent Schlender, Fortune, Oct. 2, 1995.

93. Steve Ballmer interview, “Triumph of the Nerds,” part II, PBS, June 1996.

94. Jack Sams interview, “Triumph of the Nerds,” part II, PBS, June 1996. See also Steve Hamm and Jay Greene, “The Man Who Could Have Been Bill Gates,” Business Week, Oct. 24, 2004.

95. Tim Paterson and Paul Allen interviews, “Triumph of the Nerds,” part II, PBS, June 1996.

96. Steve Ballmer and Paul Allen interviews, “Triumph of the Nerds,” part II, PBS, June 1996; Manes and Andrews, Gates, 3798.

97. Bill Gates and Paul Allen interview, by Brent Schlender, Fortune, Oct. 2, 1995; Manes and Andrews, Gates, 3868.

98. Manes and Andrews, Gates, 3886, 3892.

99. Author’s interview with Bill Gates.

100. Bill Gates and Paul Allen interview, by Brent Schlender, Fortune, Oct. 2, 1995.

101. Author’s interview with Bill Gates.

102. Author’s interview with Bill Gates.

103. Bill Gates and Paul Allen interview, by Brent Schlender, Fortune, Oct. 2, 1995.

104. Bill Gates interview by David Rubenstein, Harvard, Sept. 21, 2013, author’s notes.

105. Bill Gates and Paul Allen interview, by Brent Schlender, Fortune, Oct. 2, 1995.

106. Bill Gates interview, conducted by David Bunnell, PC magazine, Feb. 1, 1982.

107. Isaacson, Steve Jobs, 135.

108. Isaacson, Steve Jobs, 94.

109. Author’s interview with Steve Jobs.

110. Steve Jobs presentation, Jan. 1984, https://www.youtube.com/watch?v=2B-XwPjn9YY.

111. Isaacson, Steve Jobs, 173.

112. Author’s interview with Andy Hertzfeld.

113. Author’s interviews with Steve Jobs and Bill Gates.

114. Andy Hertzfeld, Revolution in the Valley (O’Reilly Media, 2005), 191. See also Andy Hertzfeld, http://www.folklore.org/StoryView.py?story=A_Rich_Neighbor_Named_Xerox.txt.

115. Author’s interviews with Steve Jobs and Bill Gates.

116. Author’s interview with Steve Jobs.

117. In addition to the sources cited below, this section is based on my interview with Richard Stallman; Richard Stallman, essays and philosophy, on http://www.gnu.org/gnu/gnu.html; Sam Williams, with revisions by Richard M. Stallman, Free as in Freedom (2.0): Richard Stallman and the Free Software Revolution (Free Software Foundation, 2010). An earlier edition of the Williams book was published by O’Reilly Media in 2002. As that edition was being completed, Stallman and Williams “parted on less than cordial terms” based on Stallman’s objections and requests for corrections. Version 2.0 incorporated Stallman’s objections and a significant rewriting of some segments of the book. These are described by Stallman in his foreword and Williams in his preface to version 2.0, which Stallman later called “my semi-autobiography.” For comparison, the original text of the book can be found at http://oreilly.com/openbook/freedom/.

118. Author’s interview with Richard Stallman. See also K. C. Jones, “A Rare Glimpse into Richard Stallman’s World,” InformationWeek, Jan. 6, 2006; Richard Stallman interview, in Michael Gross, “Richard Stallman: High School Misfit, Symbol of Free Software, MacArthur-Certified Genius,” 1999, www.mgross.com/interviews/stallman1.html; Williams, Free as in Freedom, 26 and passim.

119. Richard Stallman, “The GNU Operating System and the Free Software Movement,” in Chris DiBona and Sam Ockman, editors, Open Sources: Voices from the Open Source Revolution (O’Reilly, 1999).