The CD-ROM

Probably, soon the familiar storage method of such information a CD-ROM. CD-ROM stands for "read only memory CD-ROM", which means that the information on the disk can only be read, but no changes in it add impossible. CDs are a common method for displaying multimedia programs, since it stores up to 700 megabytes (MB) of information is about as much as 500 floppy disks 3,5. DVD ("digital versatile disk") can hold much more, but is used primarily for video movies.
CD-ROM drives operate much like an audio CD. Many CD-ROM drives can play audio CDs. The disk is usually made of polycarbonate coated with a layer of aluminum alloy which in turn has a plastic coating that protects from dust and fingerprints. Information is stored on disk in the form of fine depressions (bits) in the aluminium layer. In CD drive to read them use a low power laser beam. The presence of the aluminum layer bits is determined by reflection of the laser beam: a weak reflection or no it shows that Pete in this place is, and strong that it is not. The drive sends to the computer the sequence "Pete is - no sweat", and he interprets it as binary a and again turns to the text, sound, or animation.
Used now the drives are reading the CD with a laser, which generates rays in the red spectrum, but has already developed blue lasers, which allow to increase the volume of information. Now on the compact disc you can record a maximum of 75 minutes of video, and using the blue ray, in five more.
The time required for the computer to find information on the disk, called the access time. Usually it is measured in milliseconds (sec). What is the shortest access time, the faster the computer responds to your commands.
Today, the average access time for CD-ROM about 200 sec, which is almost seven times greater than the time for most hard drives. With improvements in technology the access time will certainly decrease.
Information can be read, only the laser will be positioned over a portion of the disk. The speed with which information is transmitted to the computer is called data transfer rate. It is measured by the amount of information that can be read within seconds. Early models of CD-ROM drives transferred data at the speed of around 150 kilobytes per second. Today's work 7,800 (52x) and even more kilobytes (KB) per second.
Multimedia computer systems are usually equipped with a CD-ROM drive, stereo sound system with speakers and a sound card. Sound card inserted into the motherboard of a computer. It analyzes the content of audio files and plays them through your speakers or headphones. With their help, you will be able to record audio from a microphone or any other source. Thereafter, the computer will transmit a sound wave in digital form, i.e. convert them to a string of binary numbers that are able to recognize, and retain on your disk.