The following is a Plus Edition-only article written and copyright by Richard W. Eastman."How long will a CD or DVD last?" As you might guess, the only correct answer is, "It all depends."
The one thing to remember about digital data is that there is no signal degradation in the output. In a digital environment, data is stored in "bits," often referred to as "ones and zeroes." Each bit either is there or it isn't. Analog data, however, is stored in an infinite number of signal strengths. This variable information is the problem; if not exactly perfect, the result is degraded audio or images. Analog data will degrade over time; digital data will not.
Anyone who has used both analog and digital cell phones is familiar with this difference. The older analog cell phones work well when signals are strong. As the cell phone user moves further from the cell tower being used, the signal received deteriorates, slowly introducing hiss, static, and other noises. As the signal weakens still further, the induced noise eventually overpowers the wanted signal. By contrast, digital cell phones work much better. The user does not notice any difference between a strong signal and one of marginal strength. In each case, the reconstituted audio sounds very good in the cell phone's ear piece. If the signal strength drops even further, the excellent- sounding audio simply disappears abruptly. When using a digital cellular connection, one never hears static or the hiss of "white noise." Either the received signal is good enough for perfect sound, or it is not there at all. There is no in-between condition.
The same is true for audio and video analog tapes when compared to digital disks. An analog tape can deteriorate over time and with frequent use. The hiss of white noise will grow as signal strength decreases. On video, the white noise will appear as "snow" or as a fuzzy image. The condition worsens with time and with the number of replays. Eventually, the white noise will overpower the desired signal. On the other hand, digital data, as stored on CD and DVD disks operates in loosely the same manner as the digital cell phone. The signal will appear perfect to the user for many years. When the signal finally becomes so weak as to be unusable, the result is total silence. There is never an in between period of encroaching hiss or static.
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