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Home > Optical Storage > Understanding CD-ROM and DVD-ROM Drives An Introduction To Optical Storage Technologies
Introduction And Overviews
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This page provides an overview of the mechanics of CD-ROM and DVD-ROM drives and how they work in a personal computer.
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Overview Of CD-ROM and DVD-ROM Drives

The CDROM, or Compact Disk Read Only Memory drive is a device that reads,writes and can decode data stored on a cdrom disc. Data is stored on this disc in the form of tiny pits in aluminum film. The data is organized on tracks on the cdrom in about 682 megabytes.

The CDROM uses a controller to "talk" to the PC. The Interface is the actual connection from the drive to the motherboard or expansion slot. CDROM drives are available in the SCSI, the IDE and Parallel-Port interfaces.

There are basically two types of disk storage for computers: magnetic and optical. In magnetic storage, data is recorded magnetically on rotating disks. Optical disc storage is similar to magnetic disk storage in basic operation, but it reads and writes using light (optically) instead of magnetism.

Although most magnetic disk storage is fully read and write capable many times over, many optical storage media are either read-only or write-once. Note the convention in which we refer to magnetic as disk and optical as disc. This is not a law or rule but is followed by most in the industry. At one time, it was thought that optical storage would replace magnetic as the primary online storage medium. However, optical storage has proven to be much slower and far less dense than magnetic storage and is much more adaptable to removable-media designs. As such, optical storage is more often used for backup or archival storage purposes and as a mechanism by which programs or data can be loaded onto magnetic drives. Magnetic storage, being significantly faster and capable of holding much more information than optical media in the same amount of space, is more suited for direct online storage and most likely won’t be replaced in that role by optical storage anytime soon.

Optical technology standards for computers can be divided into three major types:

■ CD (compact disc)
■ DVD (digital versatile disc)
■ BD (Blu-ray disc)

All of these are descended from popular music and video entertainment standards; CD-based
devices can also play music CDs, and DVD and BD-based devices can play the same video discs you can purchase or rent. However, computer drives that can use these types of media also offer many additional features.

The Laser Diode emits a low-level beam toward the reflection mirror. A servo motor is activated by a microprocessor onto the tracks on the disc. This is done by moving the reflecting mirror.

When the beam hits the disc, refracted lights is then focused through the first lens under the disc. It is then bounced off the mirror,and directed to the beam splitter. The beam splitter sends returning laser light to the next focusing lens. And the last lens sends the beam to a photodetector, which converts the light into electric pulses.

The microprocessor then decode these electric pulses and send them to the computer through the data cable and the controller.

When you look inside your computer you will notice that the CDROM Drive is mounted at the top in all tower units and may be mounted in an assembly at the front of the Desktop PC.

As with the Hard and the Floppy Drives,the CDROM Drive processes data with the help of the Controller which may be mounted in an expansion slot but in most cases it will be mounted directly unto the motherboard. The drive and controller are connected by the Ribbon Cable which allows the data to flow back and forth as needed.

At the rear of the CDROM Drive you will see a Jumper which is used to assigned the drive as the Master drive or the Slave drive. Since the CDROM is can be used to play music on compact disks, the Sound Card is connected at the rear of the cdrom drive. At the other end of this connection you will see the Power Supply connector.

Take the time to remove the cover of your PC and get to know each and every component. Study the location of your CDROM drive and how its mounted in the System Unit. By doing so you will become more confident about understanding your computer system.

How To Install A DVD-ROM Drive
This document will outline the steps required to install a DVD-ROM drive into your computer. You'll learn the basics of how to configure the drive for proper installation.
Read Full Article
How To Boot Your Computer Directly From An Optical Drive
This document will outline the steps required to boot your computer directly from an optical storage drive, for the purpose of troubleshooting your computer or reinstalling an operating system.
Read Full Article
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Cables and Connectors Cases CD-ROM and Optical storage mediums Central Processing Units Floppy disk drives Hard disk drives Computer memory Modems and routers Computer monitors