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职称英语理工类考试考前每日一练 Compact Disks 1 If someone says to you your music CDs dont really hold any music on them，and they only have numbers recorded on them，you may not believe it.In fact，he is right in that sound is actually recorded onto the CDs as special numbersa digital codel。The code is pressed onto the CD as bumps on a long spiral track almost five kilometers long. These bumps are an average of 0.5 microns wide 2 A small laser bearn shines onto the bumDs as the CD turns.The light is reflected back to a receiver that records how the laser light bounces back.This lets the CD player2 turn the reflected light back into the original code.This means you can hear the original code as music. 3 Digital codes are used with many technologies.Email needs these kinds of code numbers.Space probes cornmunicate with their ground station on earth using digital codes.Bar codes are read as digital codes in computer systerns.Digital communications with cell phones need digital codes.Weather radios also tune in to specific signals using these codes. 4 There are many types of compact disks.One format is called CDRWs.They can be recorded on and rerecorded onas you would do with a floppy disk3.Another format is the CDROM。The technology for recording on these disks is different from other CDs.These CDs have a dye layer that the CD writer can darken or leave clear.The clear and dark spots are the digital code.CDROM stands for Compact DiscRead Only Memory4。This disk is like asuperfloppy disk that can hold lots of information.One CDROM can hold the same amount of data as 500 floppy disks.Information is permanently recorded onto it.Computer games and other programs are considered to be CDROMs. | 
