CD-WORM

CD-R (CD-recordable) is a writable, nonerasable disk, also called CD-WORM or CD-WO (CD-write once). Permanent marks are produced by a focused laser beam. The definition of the CD-R format and of the erasable—rewritable EOD /MO-R format is put down in the Orange Book (Philips/Sony). 

Polymers are only marginally important in main memories of semiconductor technology, except for polymeric resist films used for chip production. For optical mass memories, however, they are important or even indispensable, being used as substrate material (in WORM, EOD) or for both substrate material and the memory layer (in CD-ROM). Peripheral uses of polymers in the manufacturing process of optical storage media are, eg, as binder for dye-in-polymer layers or as surfacing layers, protective overcoatings, uv-resist films, photopolymerization lacquers for repHcation, etc. 

A special implementation of the CD-R disk is the Photo-CD by Kodak which is a 5.25 in. WORM disk employing the dye-in-polymer principle for storage of up to 100 sHdes /pictures on a CD (after data compression) with the possibhity of interactive picture processing. 

The principal use of CD-ROM and WORM disks is essentially substitution of data storage on paper or microfiche. Conservative estimates number the worldwide use for data storage by paper at 91%, microfiche at 4%, and in electronic media at 5%, of which 4% are magnetic and 1% optical media (18). CD-ROM is being used as an electronic counterpart to print media the WORM disk presents itself more and more as a substitute for paper to store archivable, forgery-proof documents. 

Another advantage of PC technology is the plaimed and partially realized use of multiftmction drives for operation of either CD-ROM, WORM, or PC-R disks alternatively in the same disk drive. This is technically feasible, since for reading (in CD-ROM, WORM, PC-R) as well as for writing (WORM, PC-R) similar principles and hardware are used (108). However, the reflectivity change of PC disks (40/70%) is in general lower than the CD-ROM standard (30/70%) requires. 

Glass substrates are used commercially for 5.25 in. EOD(MOR) disks only by a few manufacturers (eg. Philips, Hitachi) in contrast, for CD-ROM and WORM memories with disk diameters exceeding 5.25 in. (eg, 12 in. and 14 in.), glass substrates are employed frequently. 

Polycarbonates. Currently, all audio CDs (CD-AD), all CD-ROM, and the biggest fraction of substrate disks for WORM and EOD worldwide are manufactured from a modified bisphenol A—polycarbonate (BPA-PC) (3). In 1991, some 1.3 x 10 compact disks were produced, equivalent to an annual amount of about 35,000 t BPA-PC. WORM and EOD disks are manufactured mainly from BPA-PC for sizes of 5.25 in. and below, and glass for larger form factors (eg, 12 in.), partially also from BPA-PC, and in some cases from aluminum or from cross-linked polymers (epoxy resins) (190). 

Modification of BPA-PC for adaptation to the conditions of production of CD and CD-ROM disks, and of substrate disks for WORM and EOD was necessary. BPA-PC standard quaHties for extmsion and injection mol ding have, depending on molecular weight, melt flow indexes (MEI), (according to ISO 1130/ASTM 1238 in g/10 min at 300°C/1.2 kg, between less than 3 g/10 min (viscous types) up to 17 g/10 min. For CDs and optical data storage disks, however, MEI values exceeding 30 g/10 min, and for exceptionally short cycle times (5—7 s) even >60 g/lOmin are demanded at an injection mass temperature of 300°C (see Table 5). 

Poly(methyl methacrylate). PMMA offers distinct advantages over BPA-PC with respect to significandy lower birefringence, higher modulus, and lower costs, but has not been successhil as a material for audio CDs and CD-ROM as well as a substrate material for WORM and EOD disks because of its high water absorption (which makes it prone to warp) and its unsuitabiUty for metallising, and less so because of its low resistance to... 

WORM disks with diameters of 130 mm (5.25 in.) and 200 mm (8 in.) are manufactured almost exclusively from modified BPA-PC, including Kodak s Photo-CD. Glass is used predorninandy only for WORM disks with 300 mm (12 in.) diameter. 

There is no competitive situation for data storage disks with embossed iaformation (CD-ROM) and recordable/nonerasable disks (WORM) no counterpart to CD-ROM and WORM exists among magnetic memories. EOD drives are best compared to floppies and removable hard disk media given their possibiUty of easy and problem-free disk exchange and a capacity on the order of that of removable magnetic media (Tape, Bernoulli, SyQuest). 

The acceptance of optical data storage iato the mass storage market, which is as yet exclusively dominated by magnetic systems, will be fundamentally boosted if optical drives and media are subject to uniform standards and become fully compatible, and multiuser drives are offered which enable the user to employ alternatively CD-ROM and EOD disks, and maybe WORM disks as well (and CD-R disks, respectively). A prerequisite, however, will be whether rewritable optical memories will use the MOR or the PCR process. This accord especially will be hard to reach. 

A viable real-time recording disk medium was developed in the mid 1980s, which became known as WORM (Write Once Read Many). However, there was no common standard for the medium, hence media produced by different manufacturers were incompatible, each requiring its own unique hardware. It is therefore not surprising that growth in this area was restricted and prices remained high.196 This is in direct contrast to the industry-wide standards which helped lead to the successful introduction of CD technology. 

CD-R was something of a surprise invention as, in the late 1980s, most of the major manufacturers in the optical memory area were commercializing the non-standard and relatively expensive WORM media, while focusing their research and development efforts on erasable optical storage. It was also believed that a writeable CD-Audio/CD-ROM-compatible medium was not feasible, due to the high reflectivity needed to meet the CD standard as defined by the Red and Orange Books.196... 

For WORM media, the film absorbance and reflectivity should both be high in the 775-830 nm range. For CD-R media the reflectivity should be high and the absorbance small but finite from 775 to 830 nm. For DVD-R, the requirements are the same as for CD-R, except that the critical wavelength range is 630-650 nm.196... 

Results show that for Cd (i) birds of prey are always more sensitive that beasts of prey and (ii) bioaccumulation is lowest in the food chain Soil —> worm —> bird/mammal. The latter food chain to birds of prey is by far the most critical pathway for Cd exposure, leading to very low critical limits for soils (approximately 0.1 ppm,... 

CD/Rs are write once/read many (WORM) storage discs. They cannot be erased once they have been written on. 

The main interest in this book is the use of laser addressable dyes in optical data recording, specifically WORM (write once read many times) used in the industrial and institutional arena for the mass storage of data, and CD-R used in smaller scale computing, educational and entertainment outlets. 

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