A solid-state drive (SSD) is a media that uses flash modules to store info. The solid-state drives remain fairly new and more expensive compared to standard hard disk drives (HDD), but they are faster, so they are ordinarily used for Operating Systems and applications on both home PCs and web servers. An SSD is recommended because it doesn't have spinning disks that limit its speed and could cause overheating like it may happen with an HDD. Most companies use SSDs for caching purposes, so any content which is accessed more often will be kept on this type of drives, while all other content will be held on conventional HDDs. The main reason to use such a setup is to balance the cost and overall performance of their website hosting platform and to minimize the load on the HDDs caused by countless reading and writing processes.