Compact Disc (CD) is a optical data storage that was originally designed for music storage and playback.
Compact Disc, Read-Only-Memory (CD-ROM) is an adaptation of the CD that is designed to store computer data in the form of text and graphics , as well as hi-fi stereo sound.
It is popularly used to distribute computer software, including games and multimedia applications . Some CDs hold both computer data and audio, with the later versions are capable of being played on a CD player.
The CD-ROM standard was officially introduced in 1982 when Philips and Sony agreed on the 4.72-inch size format we now use today.
Later, as Phillips and Sony continued cooperation in the 1980s, additional specifications were announced concerning the use of CD technology for computer data, which evolved into computer CD-ROM drives used today.
CD-ROM drives are CD-Players inside computers that can have speeds in the range from 1x and beyond, and have the capability of playing audio CDs and computer data CDs. Figure below shows the picture of the front and back of a standard CD-ROM drive.
CD drive focuses a laser beam on the track of bumps. When the laser passes over a flat area in the track, the beam is reflected directly to an optical sensor on the laser assembly. The CD player interprets this as a 1. When the beam passes over a bump, the light is bounced away from the optical sensor. The CD player recognizes this as a 0.
ADVANTAGES OF CD-ROM More durable than the standard floppy disks. CDs are not magnetic media and thus are not subject to the same dangers posed by proximity to electrical sources or magnets. Sturdiness A CD is read-only, which prevents accidental erasure of programs or files. Data cannot be changed CD-ROMs are audio-capable, allowing special compression of audio, image, and video data. They can be used to play standard audio CDs and have the capacity to store and record video data. Special capabilities The CD is a portable medium. Portability Up to 650 MB of data fit on a CD. Large storage capacity Description Advantages
To increase the storage capacity even more, a DVD can have up to four layers, two on each side. Here is a list of the capacities of different forms of DVDs:
DVD VS CD 4 hours 7.95 GB Single-sided/Double-layer 8 hours 15.9 GBOver Double-sided/Double-layer 4.5 hours 8.75 GB Double-sided/Single-layer 2 hours 4.38 GB Single-sided/Single-layer Approximate Movie time Capacity Format
These are pressed similarly to CDs. The reflective surface is silver or gold colored. They can be single-sided/single-layered, single-sided/double-layered, double-sided/single-layered, or double-sided/double-layered.
2 . DVD-R (DVD-Recordable)
Can record up to 4.5 GB in a similar fashion to a CD-R disc. Once recorded and finalized it can be played by most DVD-ROM players.
Can record up to 4.7 GB in a similar fashion to a CD-RW disc.
4. DVD-R DL (DVD-Recordable Double Layer)
A derivate of DVD-R that uses double-layer recordable discs to store up to 8.5 GB of data.
5. DVD-RAM (DVD-Random Access Memory)
Another kind of rewritable DVD. Requires a special unit to play 4.7GB or 9.4GB recorded discs. It is considered a highly reliable format, as the discs have built-in error control and a defect management system.
Blu-ray Disc uses the blue-violet laser technology to read data, in contrast to the red laser technology used in traditional DVD formats.
A Blu-ray disc, can hold up to 27GB of data on a single-sided single layer disc (compared to the traditional DVD’s 4.7GB capacity), which amounts to about 12 hours of standard video or more than 2 hours of high-definition video.
A dual layer Blu-ray Disc can store up to 50GB, almost 6 times the size of a dual layer DVD at 8.5 GB.
CD ROM drive reads data from a CD-ROM. The drives are internal (fit in a drive bay), or external (plug in). Most drives connect to an IDE channel or SCSI port. These drives come with various speed from 1x to 32x speed.
2. CD-RW Drive
Also known as CD burner. The drive not only can read data from CD-ROM, but it also can write or rewrite data to CD-R or CD-RW.