It doesn't have so much to do with the width of the tape as it does with the length of the tape and the speed it is recorded at and the difference between analog and digital. Magnetic tape has (this is basic so don't hold me to specifics) a stripe down one edge that contains timing ticks, and the rest of the tape width is used to store the actual analog data, usually sound information. Stereo recorders broke that area down into two stripes, one for each channel. Magnetic tape is very, very thin and a whole bunch can be wound onto a relatively small reel. Fresh magnetic tape has all of its lines of magnetic force aligned parallel to the tape length. As the tape is passed over the recording heads, the heads use an electromagnet to alter the shape of the magnetic lines of force on the tape. If the tape is passed more slowly over the heads, the information stored in the magnetic alterations is more densely packed. If the tape is passed over the heads faster, the data is more spread out. Slower recording speeds can cause playback to sound "mushy" because of errors caused by interference from data stored nearby being read in error due to the more densely packed data. When the data is recorded at a faster speed, that isn't as much of a problem and the recording is of a higher quality when played back. Therefore, the same reel of magnetic tape can hold various amounts of data when specified by the time. This is the exact same concept as in VCRs with standard, long play, and extended play. A standard 2-hour VHS tape can record 2 hours at standard speed (highest quality and fastest speed), 4 hours at long play (lower quality, slower speed) and 6 hours at extended play (lowest quality, slowest speed). The VCR knows what speed a tape was recorded at by reading the time-tick stripe. In any case, magnetic media is analog in nature because as the tape passes over the heads there is a continuous changing signal. CDs are a different animal entirely. Instead of a continuously changing signal, a CD has a surface that contains a finite number of discrete areas spaced regularly in rings around its circumference. Although you can't see them with your Mark I eyeballs, the surface has "pits" in it in some of those discrete areas. A laser shines on the disk surface as it rotates and is reflected back into a sensor. The light reflects back differently when the laser hits one of the pits than it does when it hits a non-pitted area. Therefore, you have a digital signal -- one that is either on or off, yes or no, and never anything in between. The specific pattern of on and off can translate neatly into digital information that can be read by computers. Increasing or decreasing the speed the disk rotates only allows more information to be read faster, it doesn't change the density of the data stored and it doesn't affect the quality of the playback. The only ways to increase the actual amount of data stored on a CD is to either increase the size of the disk to allow more information to be stored on it or to decrease the size of the pits so more can fit on the disk. The smaller the pits get, the more precise the engineering of the disks and the drives needs to be, which is why we're seeing larger and larger optical disks now as the technology is refined. Standard CDs can hold 640 megabytes (or something on the order of 687 billion pits), while DVDs, which use the same basic technology, can hold approximately 4 gigabytes (or something over 105 trillion pits, if I've done my sums right). The new high def DVDs coming out soon will be able to hold 30 to 50 gigabytes of data. Gee, I hope my response isn't overkill :) Ron > > In a message dated 2/8/05 11:05:05 AM Central Standard Time, > Madrachod@xxxxxxx writes: > > << Then, why is it that a cd can only hold 79:57 of music and an open reel > tape can hold up to 6.5 hours (or more) per-side. >> > > Could it be because you have the entire width of the tape to > record on, instead of essentially just a point? Gary > For a web-based membership management utility and information on list > policies, > please see http://nibec.com/24hoursupport/ > > To unsubscribe, send a blank email to 24hoursupport-request@xxxxxxxxxxxxx > with > "unsubscribe" (without quotes) in the subject. > > For a web-based membership management utility and information on list policies, please see http://nibec.com/24hoursupport/ To unsubscribe, send a blank email to 24hoursupport-request@xxxxxxxxxxxxx with "unsubscribe" (without quotes) in the subject.