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DVD Technology DVD, the Digital Versatile Disc, is a high capacity CD-size disc for video, multimedia, games and audio applications. Capacities for the read-only disc range from 4.7GB to 10GB, with 17GB in development. Recordable and re-writable versions have alse been developed. Although identical in appearance, DVDs and CDs differ in a number of key physical parameters. To meet the requirements for 133 minutes of high quality video on one side of a single disc requires the use of a thinner (0.6 mm) substrate, two of which are bonded together. DVD 5 discs comprise a sandwich of two 0.6mm discs, one metallised and with data, the other blank, bonded together. Labels can be printed on the discs conventionally. DVD 9 discs comprise one semi-reflective substrate (layer 0) and one fully metallised substrate (layer 1) bonded together with an optically transparent layer. Labels can be printed on the discs conventionally. DVD 10 discs comprise two metalised substrates bonded together and read from both sides. The disc label is restricted to an annular area within the disc hub, on both sides of the disc. DVD 18 discs comprise two dual-layer substrates bonded together and read from both sides. Such discs are much more difficult to make and require special equipment that is not yet available. The disc label is restricted to an annular area within the disc hub, on both sides of the disc. DVD-R and DVD+R discs are write-once, single sided, single layer discs, with a capacity of 4.7GB (aproximately equivalent to a DVD 5). DVD+R DL discs are write-once, single sided, double layer discs, with a capacity of 8.5GB (aproximately equivalent to a DVD 9). DVD-RAM discs are re-writable discs with a capacity of 4.7GB per side. Other re-writable formats, such as DVD-RW and DVD+RW, are also available as alternatives to DVD-RAM. Bonding After metallising, the two substrates are bonded together with the metallised surfaces on the inside of the sandwich, normally using a UV-cured lacquer. For DVD-9, the bonding layer must be optically transparent, uniform and of the correct thickness with no bubbles or other defects. Hot melt bonding can be used as a bonding technique for DVD-5 and DVD-10 discs but is not suitable for DVD-9 discs. DOCdata does not use it. Disc Finishing Printing of single sided DVD discs can be the same as CDs, e.g. using Screen-printing of up to six colors, or CMYK offset litho printing. Double-sided discs can only be printed within the hub area on both sides. New Packaging has been developed for DVD to differentiate it from CDs. Quality Assurance DVD discs must meet
certain stringent quality parameters, the most important of which are:
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