There's been a lot of articles about what is "Big Data" and how does it compare to traditional Supercomputing and High Performance Computing. I thought about it, and devolved it into a simple mathematical statement.
In Supercomputing / HPC
Computation Time >> IO Time
and in Big Data
IO Time >> Computation Time
The architecture of the hardware, the networking solutions, the software you use, how you design your software, etc. etc. is centered around this simple statement.