Introduction to An Optical Disc [MiniTool Wiki]
An optical disc is a recording medium which uses the optical storage technology to read and write data. It can be divided into non-erasable discs, such as CD-ROM, DVD-ROM, and erasable discs, such as CD-RW, DVD-RAM, etc.
The Appearance of An Optical Disc
An optical disk (OD) is usually a flat, circular disk with a hole in the middle. The diameter of the disc is usually between 7.6 and 30 centimeters (3 to 12 inches), and the most common size is 12 centimeters (4.75 inches). Typical discs are about 1.2 mm thick (0.05 inches).
One side of the disc contains actual data and is usually coated with a transparent material, usually a lacquer. The reverse side of the disc typically has a printed label, sometimes made of paper, but more often is printed or stamped onto the disc itself.
Unlike floppy disks, most discs do not have an integrated protective casing, making it susceptible to data transfer problems due to scratches, fingerprints, and other environmental issues. By the way, most optical discs show a characteristic rainbow color because of the diffraction grating formed by its grooves.
Binary Coding on An Optical Disc
In computing and optical disc recording techniques, the form of pits (binary value of 0 or off due to lack of reflection when reading) and lands (binary value of 1 or on, due to reflection during reading) on a special material (often aluminum) on one of its flat surfaces encodes binary data (bits) of an optical disc.
The coding pattern follows a continuous helical path that covers the entire disc surface and extends from the innermost track to the outermost track. The data is stored on the disc by a laser or stamping machine.
The data can be accessed when the laser diode in an optical disk drive illuminates its data path, and the optical drive spins the disc at approximately 200 to 4,000 RPM or higher, depending on the type of drive, the disc format, and the distance of the read head from the center of the disc.
General Used Forms of Optical Discs
Compact discs (CDs), digital versatile/video discs (DVDs) and Blu-ray discs are currently the most commonly used forms of optical discs. As time goes on, you may encounter that CDs/DVDs become unreadable because they tend to be corrupted or scratched seriously.
CDs can store up to 700 megabytes (MB) of data, while DVDs can store up to 8.4 GB of data. Blu-ray Discs is the latest optical media that can store up to 400 GB of data (experimental). While in actual use, Blu-ray discs have 25 GB per layer, double-layer BD discs can store 50 GB, and in BDXL format: triple and quadruple layers can store 100 GB and 128 GB, respectively.
Computers can read and write to CDs and DVDs using a CD or DVD drive, and a Blu-ray is read with a Blu-ray drive. Please note that a CD drive can only read CD discs, a DVD drive can read DVD and CD discs, and a Blu-ray drive can read CD, DVD, and Blu-ray discs.
Popular optical drive formats include CD-ROM, CD-R, CD-RW, DVD, DVD-RAM, DVD-R, DVD-RW, DVD-R DL, BD-R, BD-RE, BDXL, and more.
It can be understood that "R" in these formats means "recordable" and "RW" means "rewritable". For example, DVD-R discs can only be written once, after which the data on them cannot be changed and can only be read. DVD-RW is a rewritable format, you can erase content and write new information.
These disks are typically used to: distribute software to customers, store large amounts of data such as music, images and videos, transfer data to different computers or devices, back up data from your local computer, etc.
Cautions in the Use of Optical Discs
The storage capacity of optical discs is a significant advantage over floppy disks storage medium (magnetic medias) which only have 1.44 MB capacity. Another advantage is that optical discs are more durable.
However, although the discs are more durable, environmental factors and everyday use tend to damage them. The library and archives develop optical media save programs to ensure the continued availability of the optical discs.
So, when you are using an optical disc, you should be careful. Here we will list some tips for you to save the optical disc longer.
- Owing to the influence of weather and temperature, sometimes the surface of an optical disc appears water vapor condensation. In this case, wipe the surface gently before using.
- The disc should be placed away from the magnetic field.
- It is strictly forbidden to touch the disc with a sharp weapon when the disc is idle, so as to avoid scratching.
- Due to the thin thickness, it is preferable to stack the disc within 10 sheets, or it is easy to make the disc deformation and then affect the playback quality.
- For important discs that need to be stored for a long time, it is especially important to choose a storage environment with a suitable temperature. If the temperature is too high or too low, it will directly affect the life of the disc. The optimal temperature for saving the disc is about 20 degrees Celsius.