Ars: Apple A4 CPU is a "feature-stripped ARM Cortex A8"
While much of the speculation over the iPad's Apple A4 CPU has been focused on the fact that it was a system-on-a-chip (SoC) designed by the minds acquired from P.A. Semi, Ars Technica's Jon Stokes has another take on the story.
In a Sunday post, Stokes (who claims to have an inside scoop) notes that the chip really isn't anything more than an ARM Cortex A8 that has been stripped of much of its I/O functionality. The ARM Cortex A8, running at 600 MHz, is the SoC that powers the iPhone 3GS.
Stokes goes on to note that the "A4 is a 1GHz custom SoC with a single Cortex A8 core and a PowerVR SGX GPU." What Apple appears to have done is to improve both battery life and speed by eliminating any functionality that isn't specifically required by the iPad. Common Cortex A8-based SoCs often have more onboard functions than are really required by mobile phones so that manufacturers don't need to design a special chip. As the article states, the usual Cortex A8-based SoC has infrared, RS232 serial, USB, keypad controller, and camera blocks to handle multiple input and output devices. The iPad, of course, will only need one USB port and one serial UART, both wired to the 30-pin connector at the bottom of the device.
By stripping the A4 to the essentials, the heart of the iPad expends no CPU cycles or power doing anything that is unnecessary to the function of the device. Stokes believes that the real power of the device comes from the software, not from the A4, and in his conclusion he compares the iPad to the Nintendo Wii - "... another product that relies for its success not on its processor, but on its novel interface and broadly accessible software. I'm sure that if the iPad can do for mobile computing what the Wii did for console gaming, Apple will consider it a resounding success."
With less than a month to go until the first iPads begin to make it into the hands of users, it's likely that other revelations about the hardware used in the devices will begin to make their way to the online media.