Amenable to extensive parallelization, Google's Web search application lets
different queries run on different processors and, by partitioning the overall
index, also lets a single query use multiple processors. To handle this workload,
Google's architecture features clusters of more than 15,000 commodity class PCs
with fault-tolerant software. This architecture achieves superior performance at a
fraction of the cost of a system built from fewer, but more expensive, high-end
servers.