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Parallel and distributed computing has offered the opportunity of solving a wide range of computationally intensive problems by increasing the computing power of sequential computers. Although important improvements have been achieved in this field in the last 30 years, there are still many unresolved issues. These issues arise from several broad areas, such as the design of parallel systems and scalable interconnects, the efficient distribution of processing tasks, or the development of parallel algorithms.This book provides some very interesting and highquality articles aimed at studying the state of the art and addressing current issues in parallel processing and/or distributed computing. The 14 chapters presented in this book cover a wide variety of representative works ranging from hardware design to application development. Particularly, the topics that are addressed are programmable and reconfigurable devices and systems, dependability of GPUs (General Purpose Units), network topologies, cache coherence protocols, resource allocation, scheduling algorithms, peertopeer networks, largescale network simulation, and parallel routines and algorithms. In this way, the articles included in this book constitute an excellent reference for engineers and researchers who have particular interests in each of these topics in parallel and distributed computing. I would like to thank all the authors for their help and their excellent contributions in the different areas of their expertise. Their wide knowledge and enthusiastic collaboration have made possible the elaboration of this book. I hope the readers will find it very interesting and valuable.

Permanence: The results of committed transactions will not be lost.Serializability: The results of executing transactions concurrently are the same as if they were executed serially.Use of the transaction concept to model distributed computations provides a convenient means to solve the concurrency control and redundancy management problems.' The concurrency control problem consists of three tasks: assigning an order to all transactions, identifying conflicting transactions, and synchronizing transactions to resolve the identified conflicts. Basically, there are three approaches to concurrency control: time-stamp-based schemes, locking protocols, and optimistic techniques.2

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