Electronic devices can be analog
Values on analog devices are (normally) infinitely variable. A speedometer that shows a car's speed by means of a dial is an analog device. The hand on that dial moves smoothly around the dial and can take any value that the car's engine can create. In a digital device, values are represented by numbers and therefore do not have the variability of analog devices. A standard digital speedometer, for instance, will show a car's speed as 45 mph or 46 mph, but it can't tell you when you're going 46.25 mph.
These days, people use digital most often when talking about computers and music CDs. In these devices, numbers are presented a series of ones and zeroes, called binary numbers. Each binary digit (1 or 0) is called a bit; a string of eight bits is a byte. Therefore, each byte can represent 1 of 256 values, from 00000000 and 00000001 to 11111110 and 11111111.
Computers manipulate and store information in binary form. Once the information is ready to be presented to the user, the computer converts the information to analog form. Pictures stored as digital data are converted to analog electrical signals that a monitor displays. Likewise, digitally stored sounds become analog voltages that drive speakers.
Theoretically, because digital devices cannot represent a complete, infinitely variable range like analog devices can, analog data ought to be of higher quality than digital data. For example, when music is recorded digitally, some information is lost when the sounds are converted into digital information. However, because digital information is ultimately just a string of numbers, it is easier to manipulate (with computers), can be copied infinitely without losing quality, and does not degrade over time the way analog recordings do.
And besides, digital recordings don't lose very much information. When a CD-quality digital recording is made, the computer samples (analyzes and records as a stream of numbers) the sound 44,100 times every second.