Here’s an interesting article at MacWorld on the Apple A4 microprocessor, the CPU for the iPad and the first Apple-branded system-on-a-chip: Apple inside: the significance of the iPad’s A4 chip.

With the A4, Apple still maintains its long-standing relationship with ARM while delivering on performance, with a design that no competitor can use in its own products. More to the point, the A4 puts a very critical part of Apple’s iPad under its very own control. And that move is unprecedented.

Going back to the earliest days of the Mac, Apple chose Motorola’s 68k series of chips to power its Macs because they offered better performance than Intel’s equivalent technology. In the early ’90s, the company migrated its Macs to the PowerPC architecture when Motorola couldn’t deliver a 68k processor as fast and as energy efficient as Intel’s Pentium series. Then, when the major vendors behind the PowerPC couldn’t keep pace with Intel’s Pentium IV and AMD’s Athlon series, Apple switched its Macs once more—this time to Intel’s own Core series.

Today, Macs remain beholden to Intel’s specifications. If Intel can’t keep pace, Apple will have to find yet another vendor for CPUs. But now, with the iPad’s A4, Apple has demonstrated a new option: It has the ability to take existing designs and repurpose them to give its own products better performance than the competition.