By: Timothy W. Shire
The Babylonians made good use of wet clay while the Egyptians used both ink and a form of paper to record data. The progress since that time has been directly related to the technology and materials we have at hand. Thomas Edison was able to capture sound using wax and needle, then images using silver crystals on clear acetate projecting images one after the other. With the use of electricity magnetic recording came into being first on wire then using iron oxide on plastic ribbon or sheets. The older fashioned Intel based computers still use this system by having floppy disks while at the heart of every computer is its magnetic hard disk.
The laser, which is really only light that is confined to a specific bandwidth, so-called coherent light, was discovered three decades ago and the precision to guide and control its narrow beam made it ideal for reading recorded data. The first practical use of this was the Laser video disk that came out and failed in the marketplace in 1979. However, the "CD" (compact disk) has become one of the most impressive data storing and recording devices ever developed. Though primarily thought of as a means of distributing excellent quality music it has become the standard method of handling data for computers.
The CD and other laser disk technologies are remarkably simple. Microscopic pits are made in a metallic surface indicating a one or a zero. The data stored on the disk is encoded as digital (1 or 0) information and the disk is read by a laser running over its surface and a light receiver reading the reflection from the laser. The information is decoded and reconstructed into the format appropriate to the medium be that data for a computer, sampled sounds for audio or the matrix of dots that constitute a picture for video.
The CD we use for music and for data in our computers can handle the equivalent ofover six hundred 3.25inch floppy disks of information or 640 megabytes. The contents of this document, not counting the picture is about eight kilobytes of data. By reducing the bandwidth or frequency of the laser beam that same CD sized plastic disk with its metallic sheet imbedded within it the digital versatile disk (DVD) was developed. The technology relies upon the smaller size of the laser and the tracks or spacing between each ring of information could be significantly reduced. Because of these minor changes the blank disk used must be specifically designed for the DVD but the same size of disk as a regular CD can hold 4.7 gigabytes of information.
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this article 7 kilobytes
3.25 floppy 1,400,000 kilobytes
CD 640,000,000 kilobytes
DVD 4,700,000,000 kilobytes
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The volume that can be held on a DVD is the critical mass necessary to hold a full length motion picture. However, as mention the data must be recorded in a digital format so the really important parts of this technology rests not in its hardware but in the software that encodes and decodes the data. Keep in mind that a movie consists of twenty-four pictures each second of the ninety to one-hundred twenty minutes in the movie plus its sound track which exceeds the seventy-four minutes that will fit on a regular CD and you begin to realise the need for some tricks to get things to fit. The trick is MPEG. (Motion Picture Expert Group)
MPEG was developed from the standardised algorithms developed to make compressing still images called JPEG (Joint Photographic Experts Group). The picture at the top of this page is a JPEG it is the only format that other the GIF that can be used on the web. (GIF images were developed in the 1980s by CompuServe and is a means of image compression. The small pictures that appear on the front page of Ensign are GIF images.) To give you some idea of the value of JPEG compression the picture at the top of this page is 44 kilobytes without compression that same picture would exceed 600 kilobytes. The concept of MPEG is to update the image with only those parts of the picture that have changed from one frame to the next. The process can vary in terms of complete image and updates and there are three types of MPEG standards. MPEG-1 gives a full motion picture about the same quality as VHS video tape, MPEG-2 is higher in quality and will include HDTV standards. The third form of MPEG called MPEG-4 is for low quality slow data flow applications such as picture telephones or video surveillance equipment.
By now you will have realised that the DVD is likely to become extremely common in both entertainment but also in computer technology. A wide range of applications of this technology are becoming available and it is not going to be long until all new computers sold will come equipped with DVD players which will be able to read CDs. It will depend on software to get the stuff off a DVD. If you want to see a DVD movie on your computer you need decoding movie playing software to accomplish that task. Home DVD players are fairly expensive at this point but they will rapidly become as common and inexpensive as audio CD players since the technology is no more complex. However, creating video recordings with DVD technology in the home environment is not presently expected.
The fear of duplication has created the most elaborate security system perhaps ever evolved for electronic media. The prevent material released in one part of the world from being used in another part of the world the products are being encoded with regional codes. In addition, some electronic trickery has been employed to make reproduction of material on a DVD almost impossible. The implementation of these protective security measures delayed the release and widespread use of the technology for more then five years.
To further confuse you, I think I had better let you in on some additional murky details. Earlier in this article I explained the amount of data that can be stored on a DVD, well that description was of a single sided one layer disk. Because of the use of such refined wave length sizes of the laser involved the DVD can be made with two layers on which data can be recorded. The laser is simply refocused on the upper or the lower layer of data and though this meant the widths were increased slightly the result is nearly doubling the capacity for a single side. Just to make things even more complex the DVD technology allows the creation of double sided disks with information on both sides in single layers or both sides in double layers. At its maximum with two sides and two layers a DVD can hold an astounding 17 gigabytes of information which would mean that a single disk could hold more then three full length MPEG encoded movies.
If this is still not confusing enough, the DVD system is being used on both sizes of what are now standard CD sized disks. A regular CD holds 12cm of space on which information can be record from the centre to the outside. The second size disk, the Sony "minidisk" has 8cm of space to hold information. DVDs are available in both these formats.
The DVD movie player for you television will let you play rented or purchased DVD movies but it will not replace your old reliable VHS video recorder which can time shift and catch stuff off air. However, DVDs in your computer will soon become standard to input data, to play movies you need software to permit this to happen and there will be DVDs designed to both read and write computer data. The making of DVD video disks at home or with your computer is unlikely and will for the foreseeable future be the domain of commercial companies. To create a DVD movie today you would need a minimum of $30,000 US and that would not include the cost of your computer and editing equipment.