Code-named the `` Atari 5100 '' ( a.k.a. `` Atari 5200 Jr. '' ) , only a few fully-working prototype Atari 5100s were made before the project was canceled . Code-named the `` Atari 5100 '' ( a.k.a. `` Atari 5200 Jr. '' ) , only a few fully working prototype Atari 5100s were made before the project was canceled .