The original 128K Mac from 1984 came with a single Motorola 68000 processor running at 8 MHz that could only run one app at a time. Yet today’s Macs come with multiple CPU cores that can comfortably run several substantial apps simultaneously, while running a Time Machine backup and other tasks in the background. This brief history outlines the journey between them. A processor with a single core and no support for multi-tasking runs one sequence of instructions at a time. When those call for an...