At 10 p.m. on June 29, 1975, Steve Wozniak was ready to test his odd new computer. It didn’t look like much—just a circuit board with 32 chips attached, connected to a video monitor and a keyboard.

1975: The pioneering computer-hobbyist group, The Homebrew Computer Club, holds its first meeting in a Silicon Valley garage. From its ranks will emerge industry pioneers like Apple co-founders Steve ...