Encouraging more energy efficient use of devices is an important function of an energy centric operating system. Currentcy provides a means for passing along the savings to tasks that cooperate through their usage patterns. The disk presents unique challenges and opportunities for currentcy-based policies since it has non-uniform power consumption. The cost of spinning up the disk is much greater than keeping it spinning for a short duration. In this section, we consider techniques for more efficient disk access, focusing on sharing the spinup/spindown power costs. This introduces opportunities to work with debiting, bidding and pricing in the context of our currentcy model. The policy space for these approaches is very large, and many solutions may require an API for application involvement. For example, recent work [21] describes cooperative disk I/O operations that applications can use to facilitate such behavior. In this paper, we have limited our studies to techniques for managing disk access using pricing and bidding that can be implemented solely within the operating system without application involvement.