The phonograph disks, used in olden days, to record and play sound were large in size and data was recorded in analog form. As opposed to this the data can also be stored in a compact manner, in digital format, on a smaller size optical disk. A sharply focused optical laser light can be directed on to the disk to write the data and the reflected light can be used to read the data. Large amounts of data can be stored and read, and this has given rise to the technology of optical disks, such as the CDROM, CDR/RW, DVDROM, DVDRW etc. Reading or writing to optical disks requires optical drives.

We will first discuss the optical disks and then the optical drives.

OPTICAL DISKS :

CDROM Disks :

The CDROM disks are made of polycarbonate material with a silvered reflective coating. The data is written to the disk in the form of spiral track, starting from the center of the disk and diverging out. Data can be written only once by directing a laser beam on the disk. The disk is Read Only, i.e. you can write to the disk only once and read many times. These disks are cheap and they are used to distribute photos, video clips, sound files, software etc. The maximum capacity of the disks is 650 MB.

CD-R Disks :

These are magneto-optical Disks. They are read-write disks and can be read and written to many times. The disk is coated by magnetic crystals sandwiched inside an optical medium. The data can be erased and rewritten many times. The maximum capacity of the disks is 650 MB.

Audio CD Disks :

Audio files can be recorded on this CD disk and the entire CD disk contains Audios files and songs. The  Audio CD can be played on CD ROM / R drives connected to the Computers or a separate CD Audio player.

DVDROM Disks :

A DVD disk looks similar to the CDROM disk but it stores a much larger amount of Data than the CDROM. It also uses the reflected laser beam to read the data from the disk. It can be written only once but read many times. It is formatted to store photos and large video and sound files permanently. The data on the disk cannot be erased. The maximum capacity of the disks is 4 GB. Just like the CDROM it is used to distribute photos, videos, audio files and software.

DVD -R / +R Disks: 

These are magneto-optical Disks. The DVD -R disks can be read and recorded. The data can be erased and the DVD-R can be rewritten. A large amount of data can be stored. The disks are costlier as compared to the DVDROM disks and used for storing temporary data and not for distribution of data.

One more disk is the DVD+R disc. Whereas, the DVD -R requires the data to be erased and than rewritten, the DVD +R disks can be read and rewritten, without erasing the data. The data gets written on the empty space available on the disk. The maximum capacity of the disks is 4GB.

Video DVD Disks :

The Video DVD disk contain only videos and movies along with sound in the MPEG -2 format. It is possible to record the entire videos and movies on to the DVDs in the MPEG -2 Compressed form. The Videos or  movies can be played in the DVDROM / -R / +R drives connected to the PC or through separate DVD players.

The video file has to be decompressed in order to play it. The MPEG -2 decoder may be in the form of software or hardware. In case you have the software you can install the same in your PC. In case you have an MPEG -2 decoder board, you can install the same inside the PC. In certain cases the DVD drive itself has an inbuilt MPEG -2 decoder. The video is decompressed by MPEG -2 decoder and then displayed on the screen by Windows media player.

OPTICAL DRIVES:

The Optical disks are removable, and can be taken from one place to another. Reading or writing data to the disk requires a CD /DVD Disk drive. The CD / DVD Disk drives are installed permanently into the PC. The following are the different types of Disk Drives available:

1) CDROM drives 2) CDROM / R drives 3) DVDROM drives 4) DVD –R drives
5) DVD+R drives. These drives can either have an IDE or SCSI interface.

Latest drives can also have Serial ATA interface.

We will take a short look at the construction and installations of these drives.
 
The construction of CDROM / R disk drives :

The front of the drives contains the tray to load and unload the CDs. There is a busy indicator lighting up whenever the disc is being read or written.

At the rear side of the drive there is a four pin Molex power connector. It has a 40 pin EIDE or a 50 pin SCSI signal connector. In case of EIDE drives there are jumpers for configuring the drive either as a master or a slave. In case of  SCSI drives there are jumpers to configure the drive numbers.

The inside of the drives have various subassemblies for accepting the disks, spinning the disks, reading, writing and erasing the disks A spindle motor turns the discs. The main mechanism to hold, eject, spin and read the disks is called as the CD Drive engine. The important element of the CD Drive engine is the optical assembly that contains the 780 nm , 0.6 mW gallium arsenide laser diode and detector, along with the optical focus and tracking components.

The electronics part of the CDROM contains the controller section and the drive section. The controller section contains all the interface circuits. The EIDE CDROM drive will contain the circuits of the EIDE interface, whereas the SCSI CDROM drive will contain the circuits of the SCSI interface. All the intelligence of these interfaces is contained in these circuits. The drive section contains the drive controller IC which takes care of the loading, unloading, spinning and moving the sled.

The installation of CDROM / R drives :
Step 1.
Insert the CD ROM / R drive into the bay inside your PC and secure with the screws.

Step 2.
In case of EIDE CDROM drive set the drive to either as a master or a slave, by means of jumpers on the drive. (If there are already two EIDE hard drives connected to your PC, connect a separate cable for the CDROM /R drive and set the jumper to the Master position. In case only one EIDE hard drive is connected to your PC there will be one empty connector in the data cable. Connect your CDROM to this empty connector and set the jumpers to the slave position.)

If the CDROM / R drive is a SCSI drive then set the jumper to indicate the number of the device you are connecting.

Step 3.
Connect the power cable to the CDROM / R drive.

Step 4.
Connect the data cable (50 pin in case of EIDE) or (40 pin in case of SCSI).In case there are two hard drives in your PC, connect a new cable for CDROM / R drive and setup the drive as a master. In case only one hard disk is connected to your PC, there will be an empty connector in the data cable. Connect the CD ROM / R drive to this empty connector and setup the drive as a slave.

In case of SCSI CDROM/ R connect the drive to the SCSI cables.

Step 5.
Connect the audio cable from the CD ROM / R drive to the sound card.

Step 6.
Start your PC. The windows Xp operating system will automatically detect the CDROM / R drive and install the device drivers for the drive. (as both the drive and the operating system are plug and play)

Step 7.
In case the device drivers are not installed, if Windows Xp does not have the support for your CD ROM / R drive, you can click on ‘have disk’ prompt and install the drivers from the  floppy disk supplied by the manufacturer.

The construction of DVDROM / -R / +R/ RW drives :
The DVD drives look almost identical to the CDROM/ R drives. The DVD drives can read and write the CD disks as well, apart from the DVDs. The front of the drives contains the tray to load and unload the DVDs. There is a busy indicator lighting up whenever the disc is being read or written.

The rear side of the drive is similar to the CD drives. There is a four pin molex power connector. There is a 40 pin EIDE or a 50 pin SCSI signal connectors. In case of EIDE drives there are jumpers for configuring the drive either as a master or a slave. In case of the SCSI drives there are jumpers to configure the drive numbers.

Inside the drives are the subassemblies to operate the drive. A spindle motor turns the discs. A laser assembly and laser sled causes the laser beam diode to move back and forth. The disk is inserted onto a tray. There is a mechanism to load and unload the tray.

The installation of DVDROM /-R /+R/ RW drives :
Step 1.
Install the DVDROM / -R / +R drive into the bay inside your PC and secure with the screws.

Step 2.
Set the jumper settings according to whether your DVDROM / -R / +R is an EIDE drive or a SCSI drive. If it is EIDE then set the jumper to Master or Slave.

If the DVDROM / -R / +R drive is a SCSI drive then  set the jumper to indicate the number of the device you are connecting.

Step 3.
Connect the power cable to the DVDROM / -R / +R drive.

Step 4.
Connect the data cable (50 pin in case of EIDE drive), either as a master  or slave.
Or connect SCSI cable in case of SCSI drive.

Step 5.
Connect the audio cable to from DVDROM / -R / +R drive to the sound card.

Step 6.
Start your PC. The windows Xp operating system will automatically detect the DVDROM / -R / +R drive and install the device drivers for the drive. (both the drive and the operating system are plug and play)

Step 7.
In case the device drivers are not installed, as Windows Xp does not have the support for your DVDROM /
-R / +R drive, you can click on ‘have disk’ prompt and install the drivers from the floppy disk supplied by the manufacturer.

Step 8.
Install the MPEG-2 decoder board for viewing movies or videos from the Video DVD disk. If you have an MPEG -2 decoder software then install the software in your PC.

Step 9.
Connect the video cable from the DVD drive to the MPEG – 2 decoder board. Make other connections to the MPEG-2 decoder board as given in the manual.

Reading and Writing from CD, DVD disks:

Once the CD or the  DVD drives are installed in your computer, you can read and write from the CD and DVD disks and the drive is assigned a separate alphabetical letter such as F:. For reading the CD or DVD insert the disk into the drive. Start My computer from the desktop and navigate to the CD or DVD drive, say F:  Locate the file or the folder on the disk and double click to open the folder or the file.

For writing to the disk, click on My computer. Navigate to the group of  folders or the files which you want to copy  to the CD or DVD disks. Select all the folders and the files. Click on the option to ‘Copy the files or folders to the CD’. This will write the folders or files to the CD or DVD disks. The process of writing or copying the folders and files to the CD or DVD disks is known as burning.

Besides using the operating system to burn the CDs or DVDs, you can use the specialized CD / DVD burner software called as ‘Nero’. You can install Nero software to make it easy to burn the CDs and the DVDs.