Prerequisite – Compact Disk (CD)
CD-R stands for Compact Disc – Recordable. It is a digital optical disc storage format which was introduces in 1988. CD-R is such type of compact disc that can be written only once. It can be read many times. It is made of a reflective metal disk with a layer of green or opaque bye on top. It is a blank CD in which data can be stored once and after storing data it is converted into CD-ROM.
CD-R disks can be read by most plain CD readers. It can also be read by CD readers manufactured prior to the introduction of CD-R.
History :
CD-R was initially called CD-WO (Compact Disk – Write Once). It was first developed by Philips and Sony in 1988. The specification of CD-R were published in Orange Book in the same year. Later on in 1990 it was completely in market.
Writing to a CD-R :
- A single tracks runs in spiral pattern from the center of the disc to the side.
- A high powered laser is shone onto CD-R, changing the transparency of the dye above. The transparent represents the ones and opaque represents zero.
- The disc Continues to spin and the laser follows the track. It puts the binary data onto CD-R in a spiral track.
- Finally the data has been written.
Reading from a CD-R :
- A single track runs in spiral pattern from the center of the disc to the outside.
- On the surface of the disk a low-powered laser is shone and the reflection is captured in a photodiode sensor. The opaque dye will reflect differently to the transparent dye meaning it can tell the difference between one and zero.
- The disc continues to spin and the laser follows the track.
- The binary data are put together and the CD-R has been read.
Advantages :
- It is less costly.
- It can be read by any CD player.
Disadvantages :
- Seek time in CD-R is slow.
- Data degrades with time.
- Data can not be written over in CD-R.