Scalable Computing and Communications: Theory and Practice, First Edition. Edited by Samee U. Khan, Albert Y. Zomaya, and Lizhe Wang. © 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc. 1 Scalable Computing and Communications: Past, Present, and Future Yanhui Wu, Kashif Bilal, Samee U. Khan, Lizhe Wang, and Albert Y. Zomaya 1.1 SCALABLE COMPUTING AND COMMUNICATIONS Scalability is a paradigm that can adapt to the need of computing requirements of the underlying applications and users. Scalability [1, 2] is also a desirable quality for a network, process, website, or business model. In terms of hardware, a scalable computer system may begin with one node, but more nodes can be added as and when there is a need for more computing capabilities. Scalability, when sold with IT equipment or software, is a feature to convince high-growth businesses that the future needs can be accommodated easily and without recourse to expensive machine replacement or staff retraining. However, a scalable system need not be at one physical address. The ease of availability of high-speed networks and powerful computers has led to the emergence of two computing trends: (1) cluster computing [3, 4] and (2) grid computing [5–9]. Geographically, remote desktop computers, storage systems, data sources, scientific instruments, and clusters can be combined into what are known as computational grids. Cloud computing [10–17] is an emerging paradigm in which users export data and applications (or computations) to the “cloud” (a remote set of machines) and then access the data or application in a simple and pervasive way. However, the aforementioned is a classic example of central processing. Interestingly, about 50 1 COPYRIGHTED MATERIAL