Recordable Drives

Optical devices such as CD –ROMs and DVD –ROMs are good data storage solutions. They hold a lot of data. But the biggest drawback of optical devices is that they were read only devices. To write the data in the CD or DVD, the drive is able to create the pits in the CD or DVD. The drive which possesses such feature is called the Recordable Drives. CD – R (CD writer) and CD – RW (CD rewriter) are the example of good recordable drives. Some recordable drives enable you to write data to a disc only once where as other recordable drive enable you to write the data on the same disc many times. The CD – R drives write the data only once, they can’t remove the old data from the CD and make them as a reusable. But the CD – RW able to do that.

CD – R Drive

The first writable CD – ROM drives introduced in the market in 1990s were called the CD – R. In other words we can say that it is the first CD writable drive which is able to write the data on the blank CD by crating the pits on it. At the time of their original release, both the drive and the blank discs were extremely expensive. The CD – R drive itself contains most of the same components as a regular drive, except for the special laser. The drive can also function as a regular CD – ROM drive means you can read the data from the CD as well. CD – R drives generally uses two types of speed, one for reading discs and one for writing them. The writing speed of the drive is lower than the reading speed. Generally, speaking, CD – R drives are not as fast as standard CD – ROM drives.

Like a CD – ROM drive, CD – R drives are also available or work in both IDE and SCSI interfaces. Once the CD – R drives starts writing the data to the disc, it can not be stopped until the session is completed. If the stream of data traveling to the drive is interrupted, the disc generally is ruined. More over the CD – R drives work on different types of discs called the    CD – R discs.

CD – R disc

CD – R drives works by using a different type of disc and a different type of laser beam than CD – ROM drives. The disc is still made up of the same polycarbonate material which is used in the CD – ROM drive disc, but with a spiral pregroove instead of a data pattern. This groove is the path for the track that the drive will write onto the disc.

On top of the polycarbonate layer there is a layer of a photosensitive dye, which is reflective in nature and made up of metal (such as gold alloy), and a transparent layer of protective plastic. When you purchase a blank CD, it consist only a big land, which is reflective. And the process of writing data to it involves creating pits. For crating the pits, the drive uses a special laser that causes the reflective dye layer to react with the metallic layer, forming a composite (mixed form of two) material that is almost non reflective. These non reflective areas become the pits. Such process is known as the “burning” of the CD, because a chemical reaction is carried out between the two layers by using a laser beam.

CD – R software

In addition to the drive and the blank discs, to burn CDs on your computer, you need special software. This software provides an interface by virtue of which you can select the files that you want to write to the disc. Nero, CD Burner etc. are some of the example of such kind of CD – R software.

Single Session and Multi session discs

A session is a continuous written collection of data written to a CD – ROM. The CDs of movies, songs etc are available on the market are all single session disc in which the data in written only once. But when you burn or create your own CDs, you can conceivably write multiple sessions on a disc. This means that you can write 100 MB of data today, 72 MB tomorrow, and so on until the disc is full. This is a wonderful feature provide by the CD – R soft wares, but you must have a multisession drive in order to burn CDs in this way or create a multisession CD. In addition, you need a multisession CD – ROM drive to read them. If you use a single session CD – ROM drive to read a multisession CD, then you are able to read only or see the data written during the first session not written in the other sessions.

CD – RW drive

No doubt that the CD – Rs became a popular data storage media, but as the time spent, the people want to reuse discs by erasing the old data on them and writing new data. But CD – R are not able to do that. To overcome this problem the CD – RW (CD rewritable) drives are introduced which can do the same. Once again, the CD – RW differs from the CD – ROM and the CD – R primarily in the disc medium itself and the capabilities of the laser used in the drive. A CD – RW disc consists of the usual polycarbonate substrate, but it consist five additional layers. The recording layer in which the data is stored consists of a special chemical, sandwiched between two dielectric layers that draw heat away from the recording layer. On top of these layers comes a layer of reflective metallic material, followed by a protective coating.

To perform the different types of operations, the laser in a CD – RW drive can run at three power levels, which are as follows:

Read power: The lowest power generated by the laser. Used only to read the data already written to the disc. It does not alter the state of the recordable layer.

Erase power: The laser’s middle power. Used to return the pits in an already written disc to a crystalline (reflective) state.

Write power: The laser’s highest power. Used to create the pits by changing parts of the recoding layer to an amorphous (non reflective) state.

CD – RW drives are capable of writing to either CD – R or CD – RW discs, which is an excellent feature.