CD-ROM

CD-ROM (also CDROM) is the abbreviation for Compact disk READ Only MEMORY. A CD-ROM stores digital data durably. It is after that audio CD the second application of the Compact disk.

CD-ROM in Nahaufnahme
CD-ROM in close-up

table of contents

introduction

Storage medium
CD-ROM in Nahaufnahme
general
name Compact disk READ Only MEMORY
abbreviation CD-ROM
origin
invention year of 1979
inventors Philips
reading rate (1x) 150 KB/s
data
Size of 12 cm × 1.2 mm
of storage capacity 650 to 900 MT
fastest scanning rate 52x (7.8 MB/s)
fastest reading rate 72x (10.8 MB/s)
life span (in years) 10 to 50
blank data layer
CD burner
CD-ROM mechanics

a CD-ROM stores between 650 MT (corresponds 74 minuteMusic - the conventional audio CDs) and 900 MT (100-Minuten-CDs, which can be described however in all CD burners and not be read not in all CD drive assemblies). Originally the capacity should amount to after planning of the inventors 60 minutes of music and thus oneDiameters of exactly 10 centimeters have, the CD-ROM could thus into the breast pocket of a shirt be put. The appearing arbitrary 74 minutes developed, because members of the Japanese development company gladly the 9. , However the 74 heard symphony of Ludwig van BeethovenMinutes is long, and therefore at audio CD would not have found place. Thus the companies Sony and Philips, taken part in the development, decided to extend the planned capacity. The CD-ROM has thus a diameter of approx. 12 centimeters.The hole in the center of the CD-ROM has its origin in the size old Netherlands 10 cent coin. These had the developers of Philips constantly in their purse. The size of the diameter of this coin seemed ideal for applicationto be.

Nearly all today's computer systems have a CD-ROM drive assembly, with which the data can be read. The CD-ROM is one of the few storage media, which can be read by different computer systems, the data became presupposed after the ISO-9660- Standard noted. Other common file systems for CD-ROM are for example Rockridge (UNIX) and Joliet (Windows). If a CD-ROM supports the El Torito - specification, then it is a boatable medium. All these specifications touch down however on the ISO 9660-Norm.

Thosefirst CD 1979 on a fair in Tokyo were introduced. The CD-ROM is at present the furthest common medium for distributing data and software.

The CD-ROM is one of the official CD formats, those in „the multicolored ones in such a way specifiedBooks “(Rainbow Books) are specified, in case of of CD-ROM in „the Yellow Book “(= data CDs) and „orange Book “(= recordable CD formats with multi-session ability). Only if the specifications described there are kept, the CD-ROM may do thatby Philips assigned official Compact disk - Logo carry. Further special formats, z exist. B. CD-ROM XA, CD extra, CD-i etc. Since during the production of CD-ROM (and their derivatives) certain patents by Philips and/or Sony are used, is tooexamine whether for it by the patent law owners royalties are required. The production and the selling of unlizensierten CD-ROM can be pursued or forbidden in Germany or other countries by the patentees or national places.

structure of the data medium

asCarrier medium uses here one a plastic disk (from PP) with a diameter of 12 cm and a strength of 1.2 mm. On this disk is, similarly to the record, a spiral running data track. The storage mediums are also here small recesses,so-called „pit “and „country “, which were made smaller on a scale opposite the record however by a multiple, are differently long and so it was conceived that they can be selected with the help of a laser beam. The change of “pit/country” and/or. “Country/pit” formsa 1, continuous structure “country/country” or “pit/pit” 0. Hence it follows that no representation of two following each other 1en is possible. Therefore a Umkodierung is necessary, which is realized with the 8-zu-14-Modulation. (With further 3 Merge Channelbits separately result 17 channel bitsfor a data byte.) „clay-purely “(data track) runs here from the inside outward. At the beginning of the data track a table of contents is stored. With music CDs this table of contents gives the number of music titles, which are bringing in duration and the total play duration at and with data CDsthere among other things the positions of the files and listings stored (see also file system or CDFS).

The number of revolutions is adjusted dependent on the position of the sensing system on the spiral trace, in order to ensure a continuous data scanning. Thus becomes from the sensing systeminside the number of revolutions for instance to 520 rpm and outside for instance to 210 rpm adjusted. At simple CD speed about 150 kilobyte per second is selected, about which about half is pure utilizable data. The remainder consists of additional information for error correction, coding and synchronisation.

life span

the question, how long the data can be effectively read, is open. Estimations vary between 10 and 50 years, whereby aging is very strongly dependent on variations in temperature; also sunlight leaves the mediavery many faster age. It is safe that data keep importantly shorter CD-ROM than paper or Pergament. One assumes an optimal life span can be achieved by storage with constantly 20 degrees Celsius in absolute darkness.

production

a CD-ROM consists of a plastic carrier material with aluminum coating. The digital information is applied on a spiral trace. Recesses in parts are pressed into the coating, so mentioned of pit. These reflect somewhat in former times as the intact reflectingPlaces, country to be called, since the CD-ROM are pressed by the top side and by the lower surface are read. Thus those of pit from the read side are visible not as recesses, but as hills. The transitions from country to pit,and in reverse, do not reflect the light. During the reading a weak laser beam scans the stored information.

The industrielle production of a CD-ROM begins with the Premastering. On a CD-ROM to storing data are arranged, the pertinent error recognition code (EDC/HIT A CORNER, error Detection code/error Correction code) one computes. The error recognition code serves a CD-ROM for eliminating errors during the reading by a special correction procedure (CIRC, CROSS Interleaved Reed Solomon code). With the Premastering become the actual utilizable dataalso still synchronisation bytes and header information placed in front.

With the next production step, which becomes mast ring, with the help of a strong laser beam the data from the Premastering to a photoresist duck layer transfers, washed and silvers. The negative of a CD-ROM, a glass master so mentioned develops. Inmost cases the glass master before the CD-ROM production with nickel is galvanized, for which „father so mentioned develops “.

The actual CD-ROM production (pressing) takes place in an injection moulding procedure (exact: Sprayingcoin/shape). The raw material, liquid polycarbonate, becomes with the help of the Mastersinto a form pressed, afterwards with aluminum coats and seals. Usually still another CD label in the silk-screen printing is laid on on the top side of the CD-ROM.

standards and standard

  • ISO/CInternational Electronical Commission 10149, is based on the standard ECMA-130.

Special kinds and formats

  • CD-DA (Compact disk digital audio) - classical audio CD
  • CD-i (Compact disk Interactive) - in the meantime outdated Multimedia format
  • CD-R (Compact disk Recordable) - usual, once recordable CD-ROM
  • CD-RW (Compact disk ReWritable) - less popular several times recordable CD-ROM
  • DVD (digitalVersatile disk) - follow-up format with multiple storage capacity
  • ISO 9660 - with the CD-ROM usual file system
  • UDF (universal disk format) - platform-independent file system for optical media, which ISO 9660 supplements

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