Compact disks

Chapter Compact disks

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • returns is reached. Hard disks are permanently installed in the computer. You can’t takeout and replace a hard disk. Complex software—particularly the kind involving graphics,video games and simulations, and complex mathematics—needs a lot of memory space,and as the software itself becomes more and more sophisticated, consumer demand willfollow along with it. Thus, you might see, before too long, a hard disk with several tera-bytes (TB) of capacity. A terabyte is about 106 MB. (You are invited to figure out howmany average-sized novels could be written on such a disk!)Floppy disks and diskettes can be interchanged in seconds, so there is no limit tohow much data you can sock away on them. A full-wall bookcase of floppies could havemore manuscript than you’d write in 1,000,000 years. A typical PC floppy disk comes ina flexible, square package measuring 5-1/4× 5-1/4 inches and is about 1 mm thick.These disks usually have 1.2 Mb of capacity. Larger “floppies” are used in commercialcomputers. A smaller diskette is in a rigid, square package measuring 3-1/2× 3-1/2inches and is slightly thicker than the floppy package. It holds (oddly) a little more datathan its physically larger floppy cousin: 1.44 Mb.It probably won’t be long before the memory capacities of floppy disks anddiskettes increase, so don’t take these figures too seriously.Compact disksSpeech and music are commonly stored on compact disks (CDs). This medium offersseveral advantages over magnetic tape. Some CDs can store video data.The main asset of CDs is their superior reproduction quality. All of the problems as-sociated with older vinyl disks are eliminated. There is no limit to the number of timesa CD can be replayed, because laser beams are used to recover the sound. The lasersbounce off tiny pits on the disk. Light beams, of course, do not scratch the CD; nothingmechanically rubs against the disk. A CD won’t jam because it does not move while it isbeing replayed. The data can’t be distorted by stretching, as can happen with magnetictape.Modern CD recording devices digitize the speech or music. This results in theoreti-cally infinite reproducibility, because digital highs and lows (logic ls and 0s) are unmis-takable and do not get distorted. A multigeneration reproduction (say, a recording of arecording of a recording of a recording of a recording) sounds every bit as good as afirst-generation reproduction. Of course, there’s a limit to how many digital reproduc-tions can be made without error; no system is perfect. A 500th-generation digital record-ing might have a few errors, where stray noise pulses have mutated ls into 0s or vice-versa.But a 500th-generation analog reproduction would consist of indecipherable “hash.”QuizRefer to the text in this chapter if necessary. A good score is at least 18 correct. Answersare in the back of the book.1. Because of the small size of ICs compared with equivalent circuits made fromdiscrete components:A. More heat is generated.Quiz535