Today, writable CD drives (CD-Writers or CD-Burners) are standard equipment in most new computers. A CD-Writer allows you to take audio or data files from your computer and place them on CD. CDs containing audio can be played in a CD player, or if the CDs contain data, they can be used in a computer.
CD-Writers are relatively inexpensive, as are the blank CDs they use. CDs have rapidly begun to replace cassette tapes and floppy discs as the medium of choice for storing recordings and data.
Pre-recorded CDs are mass-produced through a complicated manufacturing process which is not practical to use unless producing hundreds, thousands or millions of CD copies. However as CDs became the standard medium for audio, the demand for a simple CD recording technique grew. At the same time, computer users needed a medium that could store more data than floppy discs. In response to this demand, electronics manufacturers introduced the CD-R and the CD-Writer.
CD-Rs
CD-R stands for CD-ROM Recordable. A new CD-R does not have microscopic 'bumps' on its surface. That is, it contains no digital data. The CD-R is coated with a special chemical film coated with a light sensitive dye into which the 'bumps' can be burned using a CD Writer. When the disc is blank, the dye is translucent and light can shine through it and reflect off the metal surface. But when the dye layer is heated, it darkens so that light can't pass through it.
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By darkening particular points along the CD track, and leaving other areas of dye translucent, you can create a digital pattern that a standard CD player can read. The light from the player's laser beam will only bounce back to the sensor when the dye is left translucent, in the same way that it will only bounce back from the flat areas of a conventional CD.
A CD-Writer is used to burn this digital pattern onto a blank CD-R. A CD Writer has two lasers: a standard read laser (like a normal CD player), and a write laser. The write laser is more powerful than the read laser and is intense enough to darken the dye material on the CD-R. The weaker read laser does not affect the dye. This means that information on the disc will not be affected by the read laser.
Advantages & Disadvantages of CD-Rs
The main advantage of CD-R discs is that they work in almost all CD players and computer CD-ROM drives. CD-Rs are also the cheapest media available. They are even cheaper than most high-quality cassette tapes.
The only drawback of CD-R is that once you've burned in the digital pattern, it can't be erased or re-written. It is possible to leave out some areas on the disc for later writing, but this creates a multi-session CD. A multi-session CD can not be read properly in a standard CD Player and some older CD-ROM drives.
CD-RW
To overcome the problem that the CD-R cannot be erased or rewritten, a new format was introduced in the mid-90s, called CD-RW (or CD-ROM Rewritable). The laser of a CD-RW writer, called a CD-Rewriter, can both burn bumps into the media and also melt the media back into its original state. In place of the dye layer in the CD-R, a CD-RW disc contains a chemical compound that can change its form when heated to certain temperatures. When the compound is heated above its melting temperature, to around 600 degrees Celsius, it becomes a liquid. At around 200 degrees Celsius, it turns into a solid.
The solid form of the compound is translucent (light can show through it), while the liquid is dark. On a new, blank CD-RW disc, all of the material in the writable area is in the solid form, so light will shine through this layer to the reflective metal above and bounce back to the light sensor. To write information on the disc, the CD-Burner uses its write laser, which is powerful enough to heat the compound to its melting temperature. As with CD-Rs, the weaker read laser does not change the state of the material in the recording layer.
Advantages & Disadvantages of CD-RWs
Due to the very flexibility of the medium, CD-RW discs do not reflect as much light as the other CD formats and cannot be read by many older CD players and drives. So these are not a good choice for music CDs. However, most new drives and players, including all CD-Rewriters, can work with all the different CD formats. For the most part, they are used to back-up computer files.
CD-Rewriters can write to both CD-R and CD-RW discs, whereas CD-R drives can't write to CD-RW discs. CD-RW discs are, however, about twice the price of CD-Rs. CD-Rs and CD-RWs are written using light and for this reason should be kept away from strong direct light, as this can corrupt the information stored on the disc.
Read & write speed
CD-Writers can read and create CDs at different speeds: This is usually expressed as a combination of two figures, a read speed and a write speed. Both are written as a multiplication factor (1x or 4x or 8x and so on). At 1x (1 times) writing speed, the CD spins at about the same rate as it does when the player is reading it. This means it would take you about 60 minutes to record 60 minutes of music. At 2x speed, it would take you about half an hour to record 60 minutes, and so on. Current CD-Writers operate at 24x writing speed or faster. Faster writing speeds need a faster connection between the computer and the writer; and a blank disc that is designed to record information at higher speed.
Like the CD writer, the CD-Rewriter also works at different speeds. In fact, the device is usually specified by its write speed, its rewrite speed and its read speed. (For example a CD-Rewriter would be specified as 16 x 8 x 32. This means it can write CDs at 16x speed; it can re-write CDs at 8x speed, and can read data from a CD at 32x speed.) The speed for re-writing is often slower than the write speed, as rewriting needs the extra step of first erasing the existing data on the CD.
Internal or external CD writers?
Most often the CD-Writer or Rewriter is part of a computer, and the information written to the CD comes from a file stored on the computer. The CD-Writer can be fitted into the case of the computer (an internal writer) or can be an external unit that connects to the computer via the USB, Firewire or PC Card connections.
Internal CD-Writers are relatively easy to install, and are about twice as fast and half the price of external writers. However external writers do have some advantages:
- Installing an external writer is much easier and you don't have to open up your computer's case.
- External writers are portable. This means that the writer is not tied to a particular computer and can be connected to any of the computers at your station. It is also a good solution if you want to use the CD-Writer with a laptop computer.
- External drives are usually compatible with different types of computers.
CD burning software
Using a CD-Writer attached to your computer requires CD writing software. Basic CD writing software will be supplied with the CD-Writer. The software allows you to decide what type of CD to make (audio or data) and choose the files you want to write to the CD. Programmes such as Nero Burning Rom, Adaptec Easy CD Creator and Toast (for Apple Macintosh computers) are very popular. In many cases, the software is supplied along with the writer device itself - but these versions may be limited in function.
Writing a CD places large demands on your computer and things can go wrong. Do not be surprised if some of the CDs you are burning don't come out right. CD-Rs cannot be overwritten. This means that when an error occurs while writing the disc, you have to throw away the whole disc. If you continually have problems burning CDs, try to reduce the write speed. The most common problem when writing CDs is called a buffer underrun. This happens when the computer is unable to send data to the CD-Writer fast enough. Reduction of the write speed can overcome this problem.
Not all CD-Writers are part of a computer. There are a number of standalone CD recorders available for both domestic and professional use. Often, these have two drives that allow you to record music tracks directly from one CD to another.
| Remember that copying pre-recorded CDs raises very serious copyright issues. Breaking copyright laws can lead to legal action that could cost you a lot of money. |
These stand-alone recorders can also have audio inputs, allowing them to record incoming signals, much like a cassette or minidisc recorder. These writers are usually fast and accurate, but typically can only be used to create music CDs. Professional models are also very expensive when compared to computer-based writers.
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