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What is CD-ROM?
A
CD-ROM (Compact Disk - Read Only Memory)
is a storage medium that can hold approximately 650 MB of data, the
equivalent of more than 3,000,000 pages of text. Unlike diskettes,
CD-ROMs can't be erased and reused, hence the "read-only memory" part
of their name. CD Writers and Re-Writers are available that can store information to blankCDs. Because of their large storage capacities, these 4.75-inch
disks are used to store many of today's memory-hungry multimedia applications,
such as programs that have sound, colour graphics and video. CD Writers and Re-Writers are available for the PC that can store information to blank CDs.
Most
software packages you buy now come on CD-ROMs, and many games and
graphics programs require the CD-ROM to run even after they are installed.
If you buy a desktop or portable OPC to run the latest applications,
a CD-ROM is a necessity.
CD-ROMs
are designed the same as music CDs, except the computer versions can
process more data than just sound. Audio CDs can be played on a computer's
CD-ROM drive, and a music CD created with a computer CD-Writer can be played on a stereo CD player.
Installing
software on your PC is the first, and most obvious reason
to have a CD-ROM drive. Today's software comes on a large number of
diskettes or one CD-ROM. To save time and manufacturing costs, manufacturers
tend to put their programs on CD-ROM when they are larger than 5MB
- which would require four diskettes.
Many
applications require the CD-ROM to remain in its drive to operate
even though the program is installed on the hard drive. In applications
such as these, the operating instructions are loaded onto the hard
drive and the bulk of the information remains on the CD-ROM.
Data
on a CD-ROM is read by the CD-ROM drive's laser, which strikes the
disk's photo-sensitive dye as the drive's motor spins the CD-ROM at
varying speeds.
A
CD-ROM can hold more data than a magnetic disk within a hard drive
because of how the disks spin. A magnetic disk always spins at the
same rate. Because of this, the disk's outer sectors move faster than
the sectors closer to the centre of the disk. This means these outer
sectors must be larger to hold the same amount of data as the sectors
closer to the centre. This sacrifices storage space for quick data
retrieval.
A
CD-ROM's sectors are different. Data is stored in a single track that
spirals from the centre of the disk to its outer edge, and the CD-ROM
drive varies the rate at which it spins the disk. These two factors
allow all CD-ROM sectors to be the same size and therefore, hold more
data than their magnetic disk counterparts. CD-R and CD-RW (CD Burners)
CD-R, Recordable also called CD Writers or Burners and CD-RW, Rewriteable also called erasable or CD-E have become affordable for the PC market. With a CD-R the PC can write data or music to a blank CD. It is the ideal device for backing up your HD. In many instances one or two CD's would hold the contents of one HD. The writing speed is quite low - 4x on early or less expensive models and the read speed is also slower than a CD-ROM. More recent CD-R's are faster but the higher writing speed may be less reliable. The software accompanying the burners is somewhat complex. There are different methods of writing to the CD depending on whether it is data or music. Data recorded on a CD-R may in some situations not be able to be read by another CD ROM. Music CD's, however, will generally play on any computer CD-ROM or home stereo system. It is one device where high price tends to mean higher quality. Undoubtedly, quality and price like other components in the PC marketplace will improve with time.
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