Further resources on MPI are as follows:
http://raspberrypicloud.wordpress.com/2013/04/25/getting-hadoop-to-run-on-the-raspberry-pi/
Beowulf clusters—Duke University
http://www.phy.duke.edu/~rgb/brahma/Resources/beowulf/papers/ICPP95/icpp95.html
http://www.intel.com/pressroom/kits/upcrc/ParallelComputing_backgrounder.pdf
Parallel Programming—Gribble Lab
http://gribblelab.org/CBootcamp/A2_Parallel_Programming_in_C.html
http://www.redhat.com/products/cloud-computing/virtualization/