Are you thinking of the Atari 400 or 800 instead of the 2600? While there were a few cassette systems for the 2600, they're somewhat rare and the only one that

Are you thinking of the Atari 400 or 800 instead of the 2600? While there were a few cassette systems for the 2600, they're somewhat rare and the only one that allowed for writing out programs appears to have been a homebrew hack.