The USB interface has become one of the most common ways to connect an electronic device to virtually any type of computer. Netbooks, laptops, and desktop computers all feature multiple USB ports, and it is not uncommon to see at least three USB ports on even the smallest devices. This means that a USB drive can be plugged into almost any type of computer that a user might have. In this way, USB drives are much more practical than SD memory cards, as many computers do not feature slots for memory cards. Furthermore, certain USB drives can themselves be used to read memory cards for users whose computers lack memory-card slots. These special USB drives, which are a combination of flash drives and memory – card adapters, allow users to switch between storing data on flash drives and memory cards.