The PlayStation Link Cable (SCPH-1040) is a peripheral cable for the PlayStation console. Utilizing the serial I/O port found on the back of most PlayStation models, it allows for two consoles to be connected in order to play compatible multiplayer games on separate consoles.
The cable is a 12-pin inline serial cable that plugs directly into the back of the PlayStation console and was a fully supported Sony accessory for the market life of the console. Because it was only designed for original PlayStation models, it's not compatible with the redesigned PSone or PlayStation's successors.
The main advantage to using the cable was that a split-screen wouldn't be necessary for multiplayer, increasing each player's screen size and potentially increasing game performance (as only one view has to be rendered per console). However, the use of this cable requires two televisions, two PlayStations (with appropriate cables), and two copies of the game being played (with the exception of Armored Core: Master of Arena, C&C: Red Alert and C&C: Retaliation, which required only one copy as the games come with two discs).