If the PS1 has a secret port and the PS3 has a hidden secret door, why shouldn’t the PlayStation 2 have a port well camouflaged in its chassis? And in fact, the second Sony console also has a hidden port… but do you know what it was for?
Opening the door on the back of the PS2 you will find the Expansion Bay port introduced in the PS2 30000 and 50000 models and which replaces the PCMCIA slot of the 10000, 15000 and 18000 models while the port in question has been completely eliminated in the PS2 Slim model 7000 (by the way, here’s how many PS2 models exist and how to recognize them).
The input in question was used to connect an internet adapter and the hard disk drive (HDD), two peripherals that allowed the PS2 to play online multiplayer games.
Games that used the hard drive and could connect to the network included Final Fantasy XI, Resident Evil Outbreak, The Sims 2, Ace Combat 4, Kingdom Hearts, Virtua Fighter 4, and a selection of others (just a few titles).
In fact, support for the web adapter and hard drive never really caught on on the PlayStation 2, so much so that the expansion port to connect these accessories was completely removed on the PlayStation 2 Slim, one of the main differences between the PS2 Fat and the PS2 Slim.
