EclaireXL

Are there any differences from the Atari800 mode? I guess 2 joystick ports. I guess also allowing less than 48K of ram (though that could be the 800 too).

Most of this is probably not relevant here, but my understanding of the differences are:

1. Membrane vs. full-stroke keyboard.
2. It was originally sold with 8K of RAM but most sold with 16K RAM. Atari did sell a 48K RAM expansion kit but it required some soldering and was only available to dealers.
3. Single cartridge slot instead of 2.
4. Both had 4 joystick ports, but on the 400, controller port #4 is the only port that supports a light pen or light gun.
5. No composite monitor port.
6. In North America, early production was CTIA but most are GTIA. In Europe, it was GTIA.
7. As with the 800, early machines had a standard 6502 CPU. Later production units used Atari's Sally 6502.

So, I guess a good starting point would be allowing 8k, 16k or 48k and OS-A or OS-B.