In the months between the iPad's announcement and the product's launch, a great deal of attention was lavished on the A4
CPU at the heart of the new device. Apple
has been characteristically tight-lipped about the SoC's design and characteristics, but industry analysts have been determinedly chipping away at the question of what the A4 is—and what it isn't.
New information that surfaced this week indicating that the CPU at the heart of the A4 is an Intrinsity-designed 'Hummingbird' Cortex A8. There've been rumors floating around that the Samsung S5PC110 and the Apple A4 are literally identical parts, but while the two chips share the same CPU core, the A4's I/O options are trimmed considerably from those on a standard ARM processor. It's now a virtual certainty that the design team Apple acquired when it bought PA Semi had nothing to do with the A4's design; when Apple bought Intrinsity earlier this year it acquired all the IP that went into the A4 as well.
It's the A4's lack
of I/O connectivity that makes it unique among other ARM-powered configurations. When a company like Texas Instruments designs an SoC, they have no idea what sort of interfaces the buyer will want to connect it to. A normal SoC might contain interfaces for USB, PCIe, PS/2, serial ports, VGA out, and a wide variety of other standards.
Since Apple is only concerned with meeting its own needs, the company was able to divest the A4 of functional blocks that served no purpose but still drew power. The upcoming iPhone4 will also use the A4 processor, which is undoubtedly part of why Apple claims the new smartphone will deliver significantly improved features without putting too much additional strain on the phone's battery life.
With the mystery of the A4 largely solved, the next question is what Apple might be planning for its next-generation of SoC. It was always a given that the A4 was based on a pre-existing design, but all bets are off on what the next-generation of processor might look like. It'll still be awhile before we see a new chip, however—with multiple fabrication plants now pushing into 28nm production, Apple will have plenty of room to ramp the A4's performance without needing to go back to formula and start over.