Hello
Might not be able to provide a definitive answer now, but I can hopefully shed a bit of light on the subject. Firstly, it’s not just a case of number of tracks, but how large (file size) each of those tracks are. This is determined by the bit rate (quality) you originally selected when buying or ripping the tracks on I-tunes.
Essentially the higher the bit rate (better the quality) the less you will be able to fit on the Walkman (or indeed any storage device) There should be more details on this in the products instruction book
In addition, a small amount of space is used by the walkman to store and run data management functions.
Sorry I couldn’t provide specifics but hope my reply has at least pointed you in the right direction.
Best regards
Lee
