Apple Computer is beginning a wrenching tectonic shift, taking its Macintosh computer line from IBM and Freescale Semiconductor's PowerPC to the Intel Core Duo, two chip standards that have little in common -- aside from a reliance on silicon and a vocabulary limited to 1s and 0s.

The change is so radical that existing Macintosh software could have become obsolete -- if not for some near-wizardry. CEO Steve Jobs, always the showman, came to the Macworld Expo this week and unveiled two new Intel-based hardware products that have enthusiasts -- and Wall Street -- salivating. Analysts and rumormongers had been anticipating an Intel-based Mac since June, but it came as a surprise when Jobs announced not one, but two such products: a new iMac and the MacBook Pro laptop, the latter already shipping.

This rapidity was key, says Nathan Brookward, principal analyst of industry research firm Insight 64. "When Apple first announced the Intel switch in June, I was concerned sales of PowerPC Macs would slow and there would be severe software shortages for end users," he says. However, now he believes the speedy hardware roll-out could "smooth the software transition."

And there was more to Jobs' announcement. The switch to Intel had raised serious questions about backward compatibility for Apple software that runs on the former PowerPC architecture. So Jobs also unveiled an application called Rosetta, which offers interface-free emulation to translate PowerPC code into Intel code on the fly.

This application was vitally important, because the fundamental differences between Intel and PowerPC architectures mean no Mac user's library of existing software would run on an Intel-based Mac. Apple's solution, at least until developers reconfigure their applications into Intel-native versions -- a process that could be little more than a recompile or, for massive projects like Adobe Photoshop or Microsoft Office, a mammoth undertakings -- is to use Rosetta.

Rosetta is not a perfect solution, though. Even Jobs admitted in his keynote speech that the application is not an optimal solution for professional users -- some pro-level software, such as Apple's own Final Cut Pro, Logic Pro and Aperture won't run under Rosetta. And running an application under Rosetta means a drop in performance. But for everyday users, the new Mac is, well, a Mac.

Michael Gartenberg, vice president and research director at Jupiter Research, says that Apple has taken extensive steps so that "for Apple customers, the transition is almost seamless -- it almost doesn't matter."