Personal computers are better and better and they can work with sound and read CD-ROM discs. They use microchips which are for fast moving in programs. In this way are assumptions for multimedia good.

Multimedia is very used word now in present. Multimedia means using more then one media for presentation of information. It can be simple pictures in a book or difficult computers programs stored sounds, texts and video clips. These applications are today the most useful from all multimedia. Combinations of media on personal computer are very good for fun and knowledge.
Interactive multimedia enables to user direct a way of presentation of information. Connection between information is called hyperlinks interconnection and it is useful for learning programs because user can choose his own procedure when he is working.

CD ROM discs

Maybe the most used method of stored information is CD-ROM discs. Abbreviation CD-ROM means Compact Discs Read Only Memory. It means that information on disc can be only read we can not change them. CD-ROM discs are popular method of presentation. It is because on one can be 650megabyts of information. It is same amount of information which we can save on 503 and half floppy discs.

Principle of CD-ROM discs is as principle of normal audio discs and most CD-ROM mechanisms know play audio discs.
Time which computer needs for finding information on a disc is called access time. Access time of modern computer is about 200ms (mili second). It is 10x more than access time of hard disc. Long access time of CD-ROM discs makes computer needs more time for finding information. However computer technology is still better and access time is still shorter, which is good because when it is short computer do faster our needs.

Computer system usually has CD-ROM mechanism and stereo device with speakers and sound card. Sound card is card which is installing into computer. Card read context of sound sets and play them by speakers or headphones. We can record sounds by microphone or electrical instruments. Computer changes sound waves to digital form and save it on disc. Without sound card can computer makes only simple sounds.

Sound sets

Most sound card knows make and play two types of sound sets – WAVE sets and MIDI sets. Sound is waves which go through air and shake our ear drums. In cochlea are these vibrations changed into signals which brain interpreted as sound. WAVE sets save curve of wave of recording sound.
MIDI sets save instructions which are need for making sound. It can be used only for saving music and contents from information about playing tones.
Next factor on which depends quality of recording sound is number of bits which computer know save. Bit is the smallest unit of information saves in computer. More bits = better record. Sound card are most 32bits. 32bits card can distinguish and record small details too.

MP3

MP3. What is it? If you have never heard about MP3 file and wondered what it is or how it works then it will be my pleasure to introduce you „what is a MP3“. Making of MP3 file is based on compressing original music file into the file of smaller size but almost the same quality. Principle of this compression is based on imperfection of human ears, which can’t catch the whole scale of sounds. These are sound which are above or below the scale of tones which can be heard by human (above 20 000 Hertz and below 20 Hertz). The MP3 format is a compression system for music. The MP3 format helps reduce the number of bytes in a song without hurting the quality of the song's sound. The goal of the MP3 format is to compress a CD-quality song without noticeably affecting the CD-quality sound. With MP3, a 32-megabyte song on a CD compresses down to about 3 MB. For example: A size of 4 minute song is normally about 40 megabytes but after compressing it into MP3 file it has only 4 megabytes and the quality is almost about the same. This lets you download a song in minutes rather than hours, and store hundreds of songs on your computer's hard disk without taking up that much space. However, the quality of this compression wasn’t always as good as now. Before MP3s we knew MP1 and MP2 files, although these weren’t used almost at all.