The series Advances in Industrial Control aims to report and encourage technology transfer in control engineering. The rapid development of control technology has an impact on all areas of the control discipline. New theory, new controllers, actuators, sensors, new industrial processes, computer methods, new applications, new philosophies , new challenges. Much of this development work resides in industrial reports, feasibility study papers and the reports of advanced collaborative projects. The series offers an opportunity for researchers to present an extended exposition of such new work in all aspects of industrial control for wider and rapid dissemination. Hard disk drive systems are ubiquitous in today's computer systems and the technology is still evolving. There is a review of hard disk drive technology and construction in the early pages of this monograph that looks at the characteristics of the disks and there it can be read that: "bit density... continues to increase at an amazing rate", "spindle speed... the move to faster and faster spindle speeds continue", "form factors... the trend...is downward... to smaller and smaller drives", "performance... factors are improving", "redundant arrays of inexpensive disks... becoming increasingly common, and is now seen in consumer desktop machines", "reliability... is improving slowly... it is very hard to improve the reliability of a product when it is changing rapidly" and finally "interfaces... continue to create new and improved standards... to match the increase in performance of the hard disks themselves".