 The systems launched with a series of plug and play peripherals that used the Atari SIO serial bus system, an early analog of USB.To meet stringent FCC requirements, much of the circuitry of the original machines is enclosed in a cast aluminum block, which made them physically robust but expensive to produce.The 400 and 800 were replaced by the XL series in 1983, then–after the company was sold and reestablished as Atari Corporation–the XE models in 1985.