Pacheco: Chapter 1 (All), Chapter 2 (pp 15-18). Page numbers refer to text not the reader (numbers at the top of the page)
Williams: Chapter 1 (pp. 1-9; § 1.1-1.2)
Introduction to Parallel Computing, by Blaise Barney. § 1 - 2.
SUPERCOMPUTER vs your computer in bang-for-buck battle iPad 2 owns Cray-2?, by Dan Olds, Posted in HPC, 8th March 2012.