题目内容：
Compact Disks1 If someone says to you your music CDs don’t really hold any musicon them，and they only have numbers recorded 0n them，you may not helieve it． In fact，he is right in that sound is actuallv reoorded onto the CDs as special numbers—a digital code． The code is pressed onto the CD as bumps on a long spiral traek almost five kilometers long．These bumps an average of 0．5 microns wide
2 A small laser hearn shines onto the bumps as the CD turns．The light is renected back to a reeeiver that reeords how the laser light bounces hack． This Iets the CD player turn the refleeted light back int0 the 0riginal code．This means you can hear the original code as music．
3 Digital codes are used with many technologies．E—mail needs these kinds of code numhers．Space probes communicate with their ground station on earth using digital codes．Bar codes are read as digital codes 1n computer systems．Digital communications with celJ phones need digital eodes．Weather radios also tune in t0 specinc signals using these codes．
4 There are many types of compact disks．0ne fommt is called CD—RWs．Thev can be reeorded 0n and re—recorde on（rewritten on）as you Would do with a floppy disk．Another format is the CD—ROM．The technology for recordjng on these disks is different from 0ther CDs．These CDs have a dye layer that the CD writer can darken or leave clear．The clear and dark spots are the digitaleode.CD—ROM stands fnr Compact Disc—Read 0nly Memory．This（1isk is like a“super"noppy disk that can hold 10ts of information．One CD—ROM can hold the same amount 0f data as 500 floppy disks. Information is permanently recorded onto it．Computer gaines and other programs are considered t0 he CD—ROMs．
5 CDs were first sold to the public in 1982．These CDs still play well and sound fine．Current CDs are expected to last between 70 to 200 years．0f course，you can make sure your CDs last a long time by taking care of them．
6 Science keeps 0n developing．It may not be many more years before a completelv new tech．nology is inventefr and introdliced t0 the puhlic for music reeording．In the meantime．there is no doubt you wiIl continue t0 enjoy Iilstenmg to your favorite music 0n CDs6 and playing your favorite computer games on CD—ROMs．
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