a file that has an .iso extension indicates what type of file
ISO image An ISO image is a disk image of an optical disc. In other words, it is an archive file that contains everything that would be written to an optical disc, sector by sector, including the optical disc file system.[1] ISO image files bear the .iso filename extension. The name ISO is taken from the ISO 9660 file system used with CD-ROM media, but what is known as an ISO image might also contain a UDF (ISO/IEC 13346) file system (commonly used by DVDs and Blu-ray Discs).
MP3 MPEG-1 or MPEG-2 Audio Layer III,[4] more commonly referred to as MP3 (or mp3), is an audio coding format for digital audio. It uses a form of lossy data compression to encode data using inexact approximations and partial data discarding to reduce file sizes, typically by a factor of 10, in comparison with a CD while retaining a sound quality comparable to uncompressed audio. Compared to CD quality digital audio, MP3 compression commonly achieves 75 to 95% reduction in size. MP3 files are thus 1/4 to 1/20 the size of the original digital audio stream. This is important for both transmission and storage concerns. The basis for such comparison is the CD digital audio format which requires 1411.2 kbit/s. A commonly used MP3 encoding setting is CBR 128 kbit/s resulting in file of 1/11 (=9%) of the size of the original CD-quality file, that is with 91% compression.[8]