CD vs. DVD

Teach Me

In the past, if you wanted to store a large amount of data you would use magnetic tape cartridges. Unfortunately, these cartridges were slow, unstable, and expensive. Optical discs hold more data, are more stable and less expensive than magnetic tape cartridges. You may not be familiar with the term optical disc, but you probably own at least a few of them!

The main types of optical discs include:

• CD-ROM (Compact Disc Read-only Memory)—holds up to 650 MB of data on one disc; cannot be written to.
• CD-R (Compact Disc Recordable)—holds up to 650 MB of data; can be written to with special CD recording hardware and software. CD-Rs only allow you to write once to each area of the disk.
• CD-RW drives (Compact Disc Rewritable)—allows you to write and rewrite data to a CD. Holds up to 650 MB of data.
• DVDs (Digital Video Disc or Digital Versatile Disc)—can hold up to 4.7 GB of data on one disc; cannot be written to.
• DVD-Rs (Digital Video Disc Recordable)—holds up to 4.7 GB of data; can be written to with special DVD recording hardware and software. DVD-Rs only allow you to write once to the disk.
• DVD+RWs (Digital Video Disc Rewritable)—allows you to write and rewrite data to a DVD. Holds up to 4.7 GB of data.

	Today, you can buy a new computer with a drive that will play CD-ROMs, audio CDs, and DVDs. However, home DVD players are for DVD playback only, so don't try to play your CD-ROMs in them. Also, don't try to play a CD-ROM with your audio CD player—you might damage your speakers.
	Audio CDs are also optical discs, and work essentially the same way as data CDs (CD-ROM). The difference between a music CD and a computer data CD is the way in which the data is written to the CD and read back by the CD player. With the right CD recorder and software, you can create CDs in either format (or both).
	CD recorders allow you to "burn" (record data to) a compact disc. Using CD-Rs and CD-RWs you can backup 650 MB of data on CD. Using DVD-Rs and DVD + RWs you can backup 4.7 GB of data.

Show Me

Optical Devices:

• CD-ROMs and DVDs
• Reflected light to read data
• Bumps (Pits) are read in as 0s
• Flat areas (Lands) are read in as 1s
• Binary code translated by the computer into information