A solid-state drive (SSD) boosts the performance of any app running on it in comparison to an ordinary hard-disk drive (HDD). The reason is that a solid-state drive employs many different interconnected flash memory units, so there're no physical parts to move. In comparison, a hard-disk drive works by using spinning disks and each reading or writing process causes the disks to spin, meaning the speed of an HDD is restricted. Since the cost of the two kinds of drives are also different, lots of computer systems and web servers are provided with an SSD for the operating system and various applications, and a hard disk for data storage, in this way balancing cost and overall performance. A hosting service provider may also use a solid-state drive for caching purposes, so files that are used repeatedly will be saved on such a drive for accomplishing better loading speeds and for reducing the reading/writing processes on the hard drives.