updated 11:10 am EST, Mon March 1, 2010
Chip limited to iPad needs
The custom A4 processor in the iPad is in reality a castrated Cortex A8 ARM design, say several sources. Despite speculation that the chip might be based on the more advanced Cortex A9 platform, the A4 is instead said to use a single, 1GHz A8 core, paired with PowerVR SGX graphics technology. The A9 could have allowed Apple to build its first dual-core handheld.
Distinguishing the A4 is said to be the removal of unnecessary hardware, namely standard input and output architecture. It is believed that the chip may have only have one or two USB connections instead of four, and one or two serial ports rather than three, depending on how the multi-touch input controller is linked in. The A4 may also eliminate any camera-related processing architecture, since the camera itself has been stripped out.
It is meanwhile argued, as has been claimed by other sources, that the PA Semi team may not have had much if any involvement with the A4. Apple only acquired the firm in April 2008, which may not have presented enough time to do a genuinely new ARMv7 core design. PA Semi may however have shared the secrets of its PWRficient technology, which saves power by disabling unneeded sections of a chip.