A Solid State Drive (SSD) is used for storing data. It is different from a Hard Disk Drive, which spins physical disks and reads/writes to them while they're spinning. A Solid State Drive stores data in a chain of flash memory chips. The chips can be permanently installed in the computer, they can be on a removable card, and they can be in a box that fits into a laptop or desktop's Hard Disk Drive. These chips are different from the flash memory in a USB flash drive, and are faster and more reliable. For this reason, they are more expensive for the same capacity. As Hard Disk Drives have multiple spinning platters, and heads reading and writing, i.e. moving parts, there is the possibility of mechanical failure. SSD's don't have this weakness, as there are no moving marts. Everything is done electronically in the silicon chips. This makes them better for mobile applications, especially where a system failure would be catastrophic. Hard Drives have been around for about 60 years. The first one took (50) 24 inch plates to store 3.75 MB of data! That was in 1956. Today, a three inch Hard Disk Drive can hold 6 TB. Solid State Drives, which retain your data without constant power, came onto the computer scene in the late 2000's. They were very small, 1 and 2 GB, and were permanently soldered into the computer's motherboard. Now, the largest ones can hold up to 1TB, significantly less than a HDD of similar size. The reason they are still more expensive, even with such a lower capacity, is the lack of moving parts that are prone to mechanical malfunction. Over all, while SSD's are more expensive, with the same or less capacity, they are superior in speed and reliability.