As of 2015 there are two main types of hard drives in common use: mechanical hard disks drives, or HDD, that use magnetic storage technologies, and more recent flash-based solid-state drives, or SSD. Drives often differ in terms of technologies used, data transfer rates, and data and power interfaces.
Mechanical hard drives are more prone to damage from vibrations than solid-state drives, which have no moving parts. Solid-state drives also tend to have faster random and sequential read and write data transfer rates, but they typically are more expensive than traditional mechanical drives.
Hard drives also vary by the computer bus interfaces they provide. Older internal mechanical drives often use Integrated Drive Electronics, or IDE, interfaces, while more recent ones use Serial ATA, or SATA, connectors. External hard drives usually present USB or powered external SATA ports, or eSATAp. High-end solid state drives sometimes use fast PCI Express connectors.