PowerPC transition
Apple’s first processor switch was fraught behind the scenes but flawless up front, recalls
ONE OF THE advantages of the Macintosh, from its launch in 1984, was the Motorola 68000 processor, which was inherently more powerful than the IBM PC’s Intel 8088. But by the late 1980s the 68000 series was falling behind CEO John Sculley’s ambitions for the high–end market, and a Cray supercomputer was wheeled in to enable the in–house development of a brand new CPU.
The effort, codenamed Aquarius, fizzled out when it emerged that designing silicon was a very different enterprise to building computers. Its successor, Jaguar, focused on the upcoming Motorola 88110
— a new chip based on RISC technology, departing from the CISC architecture of the 68000 and 8088. The catch was that switching the Mac to RISC would mean rewriting its operating system from scratch. The prototype was a Unix–based OS called Mach, originally developed at Carnegie Mellon University in Pittsburgh by Avie Tevanian. Tevanian had since been hired by Steve Jobs’ NeXT, which was working on developing similar hardware ideas.
Meanwhile, engineer Jack McHenry started a rival backroom project, codenamed Cognac after RISC expert John Hennessy (today the chair of Google’s parent company, Alphabet). Its strategy was to develop 68000 emulation software that could quickly be adapted to any RISC chip. When plans for a new RISC series emerged in 1991 from a skunkworks collaboration between Apple and IBM, it took just a year for the PowerPC 601 processor to arrive at Apple. But Jaguar, now known as Tesseract, showed no signs of being ready to run on it.
Cognac — renamed PDM after the Piltdown Man, an evolutionary “missing link” — ran existing 68000 Mac apps seamlessly on PowerPC. Its adoption enabled the first Power Macintosh models to be launched in March 1994 running an only mildly customized version of the System 7 OS. The impossible had been made simple.