Before dismantling it, Chipworks took an X-ray image of the A4 processor to get a feel for how things are laid out inside.

If you look closely, you can see hundreds of thread-like interconnects (wirebonds) that carry electronic signals between dies.

The A4 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.