Recent laptop-class CPU dies are roughly 2-3 square centimeters and 1-2 mm thick, where most of the volume is structure not directly involved in processing. The packaging outside of the silicon is largely just making sure that heat dissipation and socket contacts are robust. RAM is a bit larger. Nonvolatile storage is often shockingly small (MicroSD as an example).
Now, without any considerations of actually powering it up or connecting the components in a meaningful way, pack a human skull full of nothing but the CPU, RAM, and MicroSD. You'd be able to pack tens of thousands of various combinations of them within an adult human skull. It's not that shocking that human brains would be more powerful than a few dozen square centimeters of silicon.
Biological brains grow as a single unit. They don't need to waste space with things like making the contacts in PCI slots far enough apart to allow for sloppy alignment. Everything can be as small as functionally possible. Everything is arranged in 3D, so you don't have to make your circuits planar, allowing you much more freedom in where you place connected pieces.
How big would cell phone hardware be without the antenna, battery, or screen?
Edited by Nypyren, 29 January 2014 - 09:13 PM.