The Entertainment Computer System (ECS) add-on module essentially added three features to the Intellivision: an additional 2K of RAM, a second sound chip and the option of plugging in a computer keyboard, a music keyboard or an additional two hand controllers.

A slate of games was started in 1982 and 1983 to take advantage of these features: Mind Strike and Scooby Doo's Maze Chase utilized the extra memory, Melody Blaster showed off the dual sound chips and music keyboard, The Jetsons' Ways With Words educational game used the computer keyboard and two sports games, Doubles Tennis and Super NASL Soccer, were designed so that two teams could compete using four hand controllers.

Still, the ECS could never shake its origin: it was rushed into production to take the place of the more ambitious but non-cost effective Keyboard Component. Neither Marketing nor the Applications Software department were ever enthusiastic about the ECS and struggled for game ideas that would justify its existence.

Just as the ECS and the first games were hitting the market in mid-1983, a new management team took over Mattel Electronics that was even less enthusiastic about the module. The Entertainment Computer System received little advertising or distribution support.

As a result, two of the best Intellivision games - Mind Strike and World Series Major League Baseball - got far less attention and sales than they deserved.