Internal storage devices are not the sole method of storing or accessing files. Desktop computers come with plenty of ports that give users with tons of options for expansion which include an external storage.
USB has been the standard all the way back in 1996. It stands for Universal Serial Bus ports that are powering most of the computer peripherals and other devices that use wires nowadays.
To name some products, desktop computer USB slots are capable of powering external hard drives, webcams, mouse, keyboards, speakers, printers and the likes from nearly all brands.
Before, computer users will be using the CD included in the product box that contain the drivers or the code that allows the computer to instantly recognize physical input commands and have their system as well to recognize and to properly use the device.
Plug and Play
Granted, a lot of manufacturers are still providing driver CD but, if you have the latest OS such as MacOS Mojave or Windows 10, the only thing you need to do is to plug the USB and the system will automatically install the driver for you.
Of course, USB technology evolves as well throughout time and the latest was of 2019 where it lets consumers to transfer data at higher speeds.