Compact disc read-only memories, or CD-ROMs, are a relatively new technology that are becoming more and more popular. These devices are used for additional storage, like hard disks and floppy disks. They can store more data than floppy disks, but not as much as hard disks.
CD-ROMs are very much similar to regular compact discs (CDs). They are hard round discs whose undersides are coated with a thin layer of light-reflecting aluminum. Using a laser, microscopic pits can be burned into this surface. This sequence of pits and flat areas stand for the 1s and 0s of the binary system, the main language of personal computers. These 1s and 0s, called bits, are how data is stored on the CD-ROM.
Information on a CD-ROM can be read using a low-power laser beam. A beam of light is reflected on the aluminum surface of the disc. When it comes to a pit, a dark spot is reflected, and when it comes to a smooth area, a light spot is reflected. The laser reflects the dark and light spots to a device called the photo detector. The photo detector then converts the light and dark spots into 1s and 0s.
CD-ROMs drives can either be internal or external. In other words, they can be built right into the computer itself, or they can be in the form of an additional device that would sit on your desk beside the computer. The internal CD-ROM drives gets its power supply directly from the computer. They are cheaper than external CD-ROM drives, but the disadvantage of them is that they cannot be moved from one computer to another. These are the most popular types of CD-ROM drives. The external CD-ROM drives are not only more expensive than the internal drives, but they are also rarely found. The advantage of these is that they can be moved from one computer to another, but the disadvantage is that there will be another bulky device taking up space on your desk.
CD-ROM drives also can come in different speeds. The speeds of a CD-ROM player are measured by how fast they can read the data. A single speed CD-ROM player can read 250,000 bytes per second. A 2X CD-ROM drive would be twice as fast as the single speed CD-ROM player while a 4X CD-ROM drive would be four times as fast! Today's technology has greatly improved CD-ROMs. These discs can be as fast as 24X or 32X! However, the most common speeds of CD-ROM drives are still only 6X or 8X.
CD-ROMs are beginning to replace floppy disks because of their fast speeds and large storage capacity. For most software programs, one floppy disk is not big enough to hold all of the information. To avoid having to use multiple disks, CD-ROMs are used.
There are also new devices that allow
you to create your own CD-ROMs. These new discs are called WORMs, or Write
Once, Read Many. Using a laser beam to burn data onto these discs, you can
create your own CDs. However, you can only write on them once, and they are
not erasable like floppy disks. Finally, there is an even newer technology
called Magnetic Optical (MO) drives. These are CD-ROM drives that, like WORMs,
allow you to record your own data. However, MOs have the additional feature
of being erasable and reusable!
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