In 1978 Dan Bricklin sat in a Harvard Business School classroom watching a professor build a financial model in chalk. Every time one number changed, each figure that depended on it had to be erased and recalculated by hand. Bricklin imagined a grid where the computer did that work instantly. With Bob Frankston he formed Software Arts in Arlington, Massachusetts, and the two spent a winter in an attic writing the program in 6502 assembly language for the Apple II.

This episode follows VisiCalc from its June 1979 launch to its end in 1985. Businessmen walked into hobby shops and bought $2,000 computers just to run a disk that cost under $100, and the phrase killer app was born. Then publisher VisiCorp spread the program across every 8-bit machine, shipped a deliberately limited version for the IBM PC, and left room for former employee Mitch Kapor to launch Lotus 1-2-3 in 1983. Within months the pioneer was collapsing.

• Advisers told Bricklin that mainframe financial programs already existed, missing that his idea was instant, personal interaction.
• The design nearly failed at 16 kilobytes of memory until falling RAM prices led Apple to ship the Apple II with 48 kilobytes.
• In 1979, more than 25 percent of all Apple II computers sold were bought for the sole purpose of running VisiCalc.
• Lotus 1-2-3 used the full power of the IBM PC and copied VisiCalc’s menu structure and keyboard commands so users could switch without relearning.
• Monthly sales fell from nearly 40,000 copies in January 1983 to 5,700 that December, and Lotus later bought Software Arts and discontinued VisiCalc.