The enclosure that he’s using is meant for a 5.25″ optical drive. It comes with a USB to SATA converter which is how he connects the hard drive to the Raspberry Pi serving the files.

An optical disc (CD, DVD) or USB drive that contains a bootable program that takes control of the computer. Computers are typically configured to look for the OS on a CD or DVD first and then the ...

(1) See USB drive and external drive. (2) A disk or disk cartridge that is inserted into the drive for reading and writing and removed when not required. CD, DVD and Blu-ray discs are optical ...