|the Size problem
It is possible (and fairly easy) to "rip" the audio data from a CD and store it into "WAV" files on a computer, and these files can be played back on demand. So ideally, you'd want to hear your music at this quality everywhere, since it's the highest quality you can typically purchase. You'd want copies of your music, at this quality, in your car, on your computer, in your portable music player, and in your stereo. Why is this not currently feasible? The answer is size.
A little math can reveal the space required to store sound information at this quality. Each sample is 16 bits, or two bytes. There are 44,100 samples each second, and since modern music is recorded in stereo, there is both a left and a right channel. This results in ( 2 * 44100 * 2 ) = 176,400 bytes to store one second's worth of samples. This means 10,584,000 bytes or approximately 10 megabytes to store just one minute of CD-quality audio. This may not sound too alarming, given many have hard drives holding tens and even hundreds of gigabytes, but it adds up quickly.
My personal music collection currently consists of 8351 songs The total playing time of all songs combined is 663 hours, 2 minutes and 34 seconds (39782 minutes total) and so would require an estimated 388 gigabytes of hard drive space to store in perfect CD-quality!!! With a little cash, a personal computer could have that much storage for now, but most portable music players have less than 1% this much space.
As video DVDs with "surround sound" audio become more popular, this will only become more of a problem: such audio typically contains 5 channels (left, right, left rear, right rear, and center), nearly tripling the space requirements! And for DVD Audio discs it's even worse: up to six channels with 24-bit samples at 96 kHz, requiring almost ten times the space!
Clearly, for the near future (at least until portable music players have hundreds of gigs of storage), you won't be able to carry around your entire music collection.
Or can you?
Fortunately, there is a solution. Compression is the technique of making a file take up less space while still containing the same information. There are two categories of compression: lossless and lossy.