A universal serial bus port (pictured below) introduced around 1997, is the gateway to your computer. It’s used to connect all kinds of external devices, such as external hard drives, printers, mice, scanners and more. There are normally two half-inch long USB ports on the back of computers built since 1998. Sometimes there are USB ports built into a hatch on the front of a computer.
If you use a USB hub (example: USB 4-Port Hub), you can connect as many as 127 devices to a USB port. It can transfer data to a speed of 12 megabits per second, but those 127 devices have to share that speed. Since USB-compliant devices can draw power from a USB port only a few power drawing devices can connect at the same time without the computer system complaining.
In 2003, USB 2.0 connectors were introduced on computers. These transfer data at 480 Mbps. Older USB devices work with USB 2.0 ports, but at 12 Mbps. USB 2.0 devices also work with older USB ports, again at the lower speed. USB 2.0 is useful for adding an external hard drive.
Add a USB 1.1 adapter to your PC:
Add USB 2.0 connectors to an older computer:
Read more about USB at: