At WWDC 2020, held entirely online for the first time, Apple announced that it would transition the Mac line away from Intel processors and onto its own custom silicon based on ARM architecture. The transition would take two years. The first Macs with Apple Silicon would ship before the end of the year.
The announcement had been rumoured for years. Apple had been making its own chips for iPhones and iPads since 2010, and those chips had been getting better at a faster rate than Intel chips for several generations. The performance per watt advantage Apple had built up in mobile was significant enough that bringing it to laptops and desktops was an obvious move on paper. The question was always when, and how Apple would handle the transition for the developer ecosystem.
The transition required two things to work. First, Apple needed Macs running on Apple Silicon to be as fast or faster than the Intel Macs they replaced, despite running a different instruction set architecture. Second, the transition needed to not break the existing software ecosystem catastrophically. A Mac that did not run the applications people relied on would not be a Mac anyone would want.
For the second problem, Apple announced Rosetta 2, a translation layer that would let Intel applications run on Apple Silicon machines without modification. Rosetta 2 used ahead-of-time translation rather than emulation, which meant performance overhead would be modest for most applications.
The first problem would only be answered by actual hardware shipping. The previous attempt to transition Mac architectures, from PowerPC to Intel in 2006, had been considered successful largely because the new Intel Macs were genuinely faster than what they replaced. Apple was clearly betting that the same would be true this time, in the other direction.
What WWDC 2020 represented was the beginning of a transition that would take Apple about two years to complete in hardware terms, but whose deeper effects would take longer to play out. The decision pulled the most premium consumer computing platform off Intel and onto a different architecture. The implications for Intel, for ARM, for Microsoft, and for the broader PC industry would unfold over the following years.