Stands for "Solid State Drive." An SSD is a type of mass storage device similar to a hard disk drive (HDD). It supports reading and writing data and maintains stored data in a permanent state even without power. Internal SSDs connect to a computer like a hard drive, using standard IDE or SATA connections.
While SSDs serve the same function as hard drives, their internal components are much different. Unlike hard drives, SSDs do not have any moving parts (which is why they are called solid state drives). Instead of storing data on magnetic platters, SSDs store data using flash memory. Since SSDs have no moving parts, they don't have to "spin up" while in a sleep state and they don't need to move a drive head to different parts of the drive to access data. Therefore, SSDs can access data faster than HDDs.
SSDs have several other advantages over hard drives as well. For example, the read performance of a hard drive declines when data gets fragmented, or split up into multiple locations on the disk. The read performance of an SSD does not diminish based on where data is stored on the drive. Therefore defragmenting an SSD is not necessary. Since SSDs do not store data magnetically, they are not susceptible to data loss due to strong magnetic fields in close proximity to the drive. Additionally, since SSDs have no moving parts, there is far less chance of a mechanical breakdown. SSDs are also lighter, quieter, and use less power than hard drives. This is why SSDs have become a popular choice for laptop computers.
While SSDs have many advantages over HDDs, they also have some drawbacks. Since the SSD technology is much newer than traditional hard drive technology, the price of SSDs is substantially higher. As of early 2011, SSDs cost about 10 times as much per gigabyte as a hard drive. Therefore, most SSD drives sold today have much smaller capacities than comparable hard drives. They also have a limited number or write cycles, which may cause their performance to degrade over time. Fortunately, newer SSDs have improved reliability and should last several years before any reduction in performance is noticeable. As the SSD technology improves and the prices continue to fall, it is likely that solid state drives will begin to replace hard disk drives for most purposes.