This book's coverage of high end server architectures is probably without rival in the entire field, but be warned that what it means by 'low end' is on a different scale to what most people would mean!

The clusters to which the title alludes are relatively tightly coupled groups of often heterogenous machines, sometimes even coupled with a specialist interconnect, rather than hodgepodge collections of random bits of hardware people have managed to find. Clusters in the commercial datacentre sense, not stone soupercomputers!

If the title made it clearer that it referred mainly to systems with hardware designed for clustering, or if the book covered 'really low end' systems as well, it'd earn a 10. So close!