A zip file is a means of sending large amounts of data over the internet.  It is compressed so that downloading it takes minutes rather than hours.  Any browser has the means to unzip or un-compress these zip files so they can be used.  Without them, downloading a music set of 30 songs could take a very long time and there would also be a much larger chance of interruption or file corruption.  Zip files are a very common way to handle large amounts of data, music, documents and photos.  So they are a good option for us to use to deliver a complete R-set of music via the internet.