Deconstructing processors like the A4 usually happens behind the closed doors of only a handful of companies. However, iFixit and Chipworks have teamed up to bring us a closer look at how semiconductor teardowns are conducted, as well as a peak inside the iPad's A4 chip. Here's part of what they found:

° The A4 package has three layers: two layers of RAM (Samsung K4X1G323PE), and one layer containing the actual microprocessor.

° This Package-on-Package construction gives Apple the flexibility to source the RAM from any manufacturer they want; they're not locked into Samsung.

° It's clear from both hardware and software that this is a single core processor, so it must be the ARM Cortex A8, and NOT the rumored multicore A9.

° iFixit and Chipworks don't expect to find any markings from PA Semi, Apple's recent acquisition, but it's safe to assume they played a major role in designing this package.

°  Every iPhone processor that we have dissected has had a Samsung part number on the processor die. The investigators haven't found any such Samsung markings on the A4 (outside of the DRAM), perhaps the clearest sign to date that Apple is now in firm control of their semiconductor design.

° Software benchmarks indicate that the A4 has the same PowerVR SGX 535 GPU as the iPhone 3GS, but verifying this via hardware analysis is quite difficult. If this is true, and it likely is, graphics performance on the iPad is fairly poor relative to the screen size.

° There's nothing revolutionary here. In fact, the A4 is quite similar to the Samsung processor Apple uses in the iPhone. The primary focus of this design was minimizing power consumption and cost.

iFixIt and Chipworks also identified several more manufacturers, including Linear Technologies, Intersil, ST Micro, NXP, Cirrus Logic, Texas Instruments, and Broadcom. More information on these parts is toward the end of the teardown.

You can find the A4 teardown at http://www.ifixit.com/Teardown/A4-Processor-Teardown/2204/1 . Also, the Chipworks lab is still running full-tilt analyzing the iPad, and they will be updating their site as they discover more; to keep abreast of developments, go to http://www.chipworks.com/Apple-iPAD-Teardown.aspx .