PDW is based on an MPP architecture. MPP architectures consist of independent processors or servers executing in parallel. Most MPP architectures implement a shared-nothing architecture, where each server operates self-sufficiently and controls its own memory and disk. Shared-nothing architectures have a proven record for high scalability and little contention. DW appliances (like PDW) distribute data onto dedicated disk storage units connected to each server in the appliance. This distribution allows DW appliances to resolve a relational query by scanning data on each server in parallel. The divide-and-conquer approach delivers high performance and scales linearly as new servers are added into the architecture.