Advances in hardware technology have created a wide performance gap between microprocessors and disks. As this gap increases, a computer system's performance is increasingly limited by the slow disk I/O activities. This thesis improves disk I/O performance by rearranging disk sectors. Usually the layout of sectors on a disk is decided by the file management system; this layout may be very different from the data access pattern generated by program execution. My disk rearrangement technique ODP attempts to place the data in a pattern that is very close to the data access pattern.