Game Shark Multi-Port Slim Playstation 2 PS2 Add 4 Players Adapter

What was the PS1's Parallel I/O port used for? - Arqade

Compatible with the Slim and Original PS2 Plug-n-Play requires no additional set-up 4 memory card slots and 4 controller ports for up to four players

PS2 Multi-tap Dual Adapter (Slim and Original)

PS2 - Cheat Device for PS2 by root670

News - August, 2016

hot sell+free shipping+New 4 Player Multitap For Sony PlayStation 2 PS2 Slim - AliExpress

Unofficial PS2 Guide (Revision 1.0), PDF, Dvd

PS2 Accessory – Page 2

ps2 console, Playstation

PS2 Accessory – Page 2

The History of The PlayStation Controller