CD-ROM Drives

The term CD-ROM is an acronym - it means Compact Disk - Read Only Memory. It ia basically a removable mass-storage device. Unlike the other mass-storage devices used by computers which use magnetics to record/read data, a CD-ROM is an optical mass storage device. The CD is created by using a laser to physically burn marks onto the surface of the disk. The data is then read by shining a low-powered laser onto the surface and reading the reflected light - the light is bright where the surface is unmarred, dull where the laser has melted the surface.

For production CD's, the CD created using the laser is used as a master to make a negative which is used to stamp out copies of the master, similar to the way vinyl record were made. The copies are then coated with a clear plastic film to protect the tracks where the information is stored.

CD's should be handled with care: the surface where information is stored works on the principle of reflected light and any scratches or smudges on that surface will cause an incorrect read-out of data. That is not very important for audio CD's - minor bits of missing or incorrect information can't usually be heard with the human ear - but is absolutely critical for data CDs, where every bit must be correct in order for the information to make sense.

Store your data CD's in protective sleeves or jewel cases and handle them (carefully!) by the edges, trying to keep your fingertips from touching the data side.

CD's can be cleaned by using soap and water and very soft rags; dry them by wiping soft rags across the CD from the center out. Carefully!

Data CD's and audio CD's can both be played in your computer's CD drive, but they are not the same. Physically they are - both formats use the same disk (120mm in diameter, 1.2mm thick, with a 15mm hole in the center) - but they are recorded differently. Error correction is a major part of a data CD but is not so important on an audio CD.

DVD's are an advanced form of a CD drive, with different methods of encoding the information on the disk and a laser beam that is split into many beams in order to read the data much quicker.

The speed of the CD-ROM drive is not nearly as important as most people think it is. Most software will work at its fastest rate if the drive is a 4x or better - 4x meets the current MPC-3 standard for information transfer. Only if a person runs multimedia software (or game software) that uses lots of audio, animation or video will the speed become important - and then faster is usually better.

CD-ROM drives can be added to most systems - one way or another. All CD-ROM drives fit in the larger (5 1/4") bays and it's usually an easy matter to connect the drive to the same IDE connectors that the hard drives are connected to (see the section on hard drives) - but sometimes that's not possible. Then you'll have to use another method. A good many of the older sound cards were built with an IDE connector that was designed to add a CD-ROM drive to systems that couldn't easily accept them. Or you could use SCSI (see the section on SCSI), especially if you had no room inside your computer's case and needed (or wanted) the drive to be external. Beware, though, that a SCSI setup requires a differently built CD-ROM drive - one that has a SCSI (50 pin) connection as well as other internal electronic differences.

CD-ROM drives have a cable connection to connect the drive to a sound card, but some of the very first sound cards didn't have the connection. If you find yourself in that position (unlikely!), all is not lost. A cable from Radio Shack can connect the earphone jack on the front of the CD-ROM drive to the Line-IN jack of the sound card for basically the same effect.

CD-Rs and CD-RWs

CD-R's & RW's are special types of CD-ROM drives. They are drives that are capable of "burning" (or making) a CD - using special software and special disks. And the CD-RW can not only write a CD but can erase and re-write special CD-RW CDs. A CD-R can be written to one time (if you make a mistake, you throw it away and start all over again with a new one) and a CD-RW can be re-used up to 100 times. As this is being written, CD-RW disks are about 5 times as expensive as CD-R disks - but the cost keeps coming down.

Creating your own CDs can be fun and useful. The large amount of information CDs hold make them wonderful tools for backing up the data on your computer. And the permanence of the data make them perfect for long-term storage of critical information. Your will on a CD? A pictorial record of all your household inventory stored on a CD, locked in your safety deposit box? All the photos you will ever take in your lifetime, digitized and stored on CDs? Let your imagination rule!

Additional Information:
     CD-R, CD-RW, DVD

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