Atari XE

After the Atari 1200XL was discontinued in 1983, Atari replaced the Atari 400 with the Atari 600XL.

The Atari 600XL had several HUGE advantages over the Atari 400:

It was lightweight and had a smaller form factor.

It featured built-in BASIC. (The Atari 400 required a separate BASIC cartridge.)

It featured a real keyboard, as opposed to the Atari 400’s hard-to-use membrane keyboard. (The Atari 400 had third-party keyboard upgrades.)

Its memory capacity could be easily upgraded to a full 64 KB by adding the Atari 1064 memory expansion module which plugged into the Atari 600XL’s rear expansion port. (At the time, the Atari 400’s memory capacity could be upgraded to 48 KB by Atari service personnel.)

It featured a built-in self-test which tested the RAM, the POKEY, and the keyboard.