I've got a Sony Attrac3 plus walkman. It plays MP3 files so you'll probally find that the salesman will claim your MP3 player does. According to the handbook with the walkman the difference between Attrac3 plus and MP3 is that the Sony system has a maximum of 255 groups and 999 files while MP3 has a maximum of 100 groups and 400 files. They also claim it compresses music content to about 1/20th of its original size while MP3 can only compress to about 1/10th.