SSDs are newer and faster data storage devices. Like HDDs, they can hold terabytes of data, but, unlike HDDs, every piece of data on an SSD can be accessed instantaneously. That means that with an SSD, you can load up large files in seconds rather than minutes.
Solid state drives outperform hard disk drives in speed while matching them in everything else —
SSDs work so much faster than HDDs that a new interface — the connection between the drive and your computer’s motherboard — had to be invented to unleash their full power. They previously made use of the SATA interface, a holdover from the days when hard disk drives reigned supreme. This allowed people to easily replace their HDDs with SSDs, which was a necessary step in the transition to solid state drives.
source, AVG