What is a CD-ROM?
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CD-ROM or "Compact Disc Read-Only Memory" is a device that can store data for access by any computer. Originally, CD-ROMs were designed for storing music and other playbacks. Now, they can store any data, including audio and video data. They are very user-friendly and extremely popular in software distribution, loading of computer games, music and photo sharing, data handling and company presentations.
CD-ROM Materials
CD-ROMs are made from polycarbonate plastic. A thin layer of aluminum is used to give it a reflective surface. It is usually 1.2 mm thick and 120 mm in diameter. There are smaller varieties namely the 80 mm diameter Mini CD and even smaller business card sized compact discs.
Innumerable very tiny pits, technically known as indentations, store data on a CD-ROM. The gaps between the pits are commonly known as lands. A laser beam aimed at the reflective surface of the compact disc reads data. The variations in the depths of the pits enable alteration of the intensity of the incoming laser beam through a system of phase shifts and interferences thereby facilitating data reading.
CD-ROM Standards and Formats
Data is usually stored on CD-ROMs in various formats. Collectively, they are known as Rainbow Books. There are Red Book, White Book and Yellow Book standards for data formatting on CD-ROMs. You can write and copy on some CDs. They are known as CD-R and CD-RW discs.
There are 98x24 byte frames containing 2352 bytes on a CD-ROM sector. 333,000 sectors are there in a standard CD. Different types of CDs have different bytes per sector available. A Video CD has 2336 bytes available out of the 2352 bytes per sector. A CD-ROM, which has three layers of error correction, is commonly known as a Mode-1 CD-ROM and contains 2048 bytes per sector. A standard CD-ROM playing time is 74 minutes or 4440 seconds. With a net byte rate of 153.6 kbps, a Mode -1 CD-ROM has a net capacity of 682 MB.
CD-ROM Manufacture
CD-ROMs are manufactured by a process known as stamping. A glass master disc is created and this is used to stamp and manufacture multiple copies of pre-pressed CD-ROMs. Recordable and Rewriteable CD-ROMs are also manufactured by the same process and data is recorded through a phase change process commonly known as burning.
CD-ROM Storage
You can store about 1000 novels on a CD. Sounds fantastic? But this is reality. A standard 120 mm CD-ROM can contain 650 or 700 MB of data. With an average of 60,000 words per novel, there can be 600,000 bytes of data in a novel considering a rule of thumb of 10 letters per word and one letter occupying 1 byte. 1000 units of such 600,000 bytes or 600 kb of data can go in a 650 MB capacity CD-ROM. Give one centimeter of book shelf space to a novel-1000 novels would require 10000 cm or 10 meters of bookshelf space. A CD-ROM can just knock out that space requirement and give you the convenience of any time, anywhere data without being weighed down by your 'bookshelf'. Compressed CDs now have an even higher capacity for data.
CD-ROMs are your best resources for smart and convenient data handling and storage. Get the best out of this unique product of scientific and technological evolution.
Happy Computing!
About the Author
Khal has been working with computers since 1982. He is the owner of the website http://www.tellmeaboutcomputers.com/CD_ROM.php
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