explain why cd-rom and online references are considered multimedia
Multimedia In common usage, multimedia refers to an electronically delivered combination of media including video, still images, audio, and text in such a way that can be accessed interactively. Much of the content on the web today falls within this definition as understood by millions. Some computers which were marketed in the 1990s were called "multimedia" computers because they incorporated a CD-ROM drive, which allowed for the delivery of several hundred megabytes of video, picture, and audio data. That era saw also a boost in the production of educational multimedia CD-ROMs.
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]