The portable format is where an SSD really shines compared to mechanical hard drives. Not only is it much faster and (usually) smaller – it’s also more robust as there are no fragile mechanical parts inside.
Most portable SSDs connect over the USB interface, but there are also a few devices available that use the considerably faster Thunderbolt interface.
There are different iterations of both the USB and Thunderbolt interfaces that may affect the performance of an external SSD.
USB SSDs are compatible with virtually all modern computers but may run at a reduced speed depending on what USB version is supported by the host. Most recent portable SSDs support USB 3.1 via either a Type C to A or Type C to C cable.
While internal SSDs have to conform to certain form factors to fit in specific sockets or slots, external solid state drives have no such restrictions. This often results in smaller and more portable formats. It only has to be sufficiently large to hold the NAND Flash memory chips, a controller and interconnecting components.