Memory under the top cover
The Atari 800's memory is on replaceable boards. Under the top cover are three RAM slots and a separate operating system module. Factory configurations ranged from 8 to 48 KB RAM. Memory was increased by replacing or adding modules; available capacity depends on the installed boards.
Cartridges and controllers
The two slots are labelled LEFT CARTRIDGE and RIGHT CARTRIDGE. Atari BASIC and most cartridges use the left slot. The right slot was intended for complementary modules; it does not run any two programs simultaneously.
There are four controller ports at the front, compared with two on later XL and XE computers. Video is available through monitor or RF output.
BASIC and software
Without a cartridge or boot disk, the 800 displays Memo Pad, a typing screen that cannot save text. An Atari BASIC cartridge starts the interpreter with the READY prompt. SIO handles disk drives, cassette recorders and printers.
48 KB RAM is sufficient for many first-generation programs. Software written for XL/XE may rely on the newer operating system and fail on the 800 despite sufficient memory.