The growing performance gap between CPUs and sustainable disk I/O is a major hurdle in supporting modern applications. As the CPUs become faster, this gap is projected to worsen, thus making it a critical problem that should be addressed with high priority. Although efficient algorithms have alleviated this problem, the mechanical nature of the disk places physical limits on the achievable speedup. On the other hand, newer technologies such as flash memory promise significant improvements in access time, power consumption, and storage density. However, the mature disk technology offers the most favorable cost per bit ratio. Since replacing standard hard disks with flash disks is prohibitively expensive, hybrid hard disks augment the standard hard disk with a small amount of flash memory. By exploiting the beneficial aspects of both technologies they aim to provide breakthrough increase in performance. Nevertheless, hybrid hard disks pose several significant design challenges. Effective and efficient algorithms to manage the flash, the disk, and interaction between them are required. To facilitate rapid and easy exploration of the design space for hybrid hard disk algorithms we present the design and implementation of a flexible and extensible simulator that models hybrid hard disks. The simulator is flexible in that it models several configurations in which the flash and the magnetic medium interact. The simulator is extensible in that it provides a simple framework to plug in several algorithms to manage the hybrid hard disk. We validate our simulator and analyze the performance of the hybrid hard disk for real workloads. / Master of Science