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The term 'optical disk' describes a range of disk types where the stored information is read by a laser. There are three main types of optical disk:
DVDs have a composite construction with the data stored between two layers of polycarbonate in the centre of the disk. Preservation and storageCDs and DVDs are not suitable for long term archival use. Data is stored on Optical disks in the form of marks or pits that either absorb or reflect the light from a laser beam. The disks have a plastic and metal layered construction that makes them susceptible to damage. Information is stored very densely on optical disks and minor damage or deterioration can cause significant information loss. There are many sources of potential damage to disks:
It is possible to clean a dusty or dirty optical disk before permanent damage occurs. Gently remove loose dust with a non-abrasive photographic lens tissue, or very soft brush. CD/DVD-cleaning cleaners can be used. Follow the directions to remove oil and dirt deposits. The cleaning motion should never be circular. Always brush radially from the centre of the disk outwards. Optical disks are normally housed in a rigid plastic jewel case. These cases are reasonably dustproof and minimise the effects of environmental change. They are usually made of an inert plastic and are suitable for long-term storage. Disks that do not have a jewel case should be individually enclosed in an inert plastic sleeve, made of polyethylene, polypropylene or Tyvek. Store disks upright in cases designed for CDs and DVDs. Jewel cases are the ideal enclosure because they support each disk at the hub and protect them from impact.
Optical disks are not regarded as long-term archival media. However, a lower temperature and relative humidity will slow their natural deterioration. The Archives provides a Standard for the Physical Storage of Commonwealth Records (pdf, 400kb) that recommends environmental conditions suitable for optical disks. Technological obsolescence is a major factor that threatens long-term use of optical disks. CDs made today can be in excellent condition in 30 years. But the data may be inaccessible if the hardware to play them or the software to interpret them has been superseded. The cost of recovering data from obsolete media and data formats is likely to be high and time consuming. It is essential to have a timely plan to migrate data from optical disks onto newer media. The best prospect for long-term retention of information on optical disks seems to be regular copying or data migration. Two solutions are to upgrade the data to current formats when you migrate the data to new media or use open source data formats. Further adviceContact the Agency Service Centre.
Are you one of the many who have a hard drive full of photo, document, and music files? Why not free up some space and save these files on CD? A standard CD-R—a CD you can save files to—can usually fit 700MB of data. The amount of files—whether photos, documents, or music—that a CD can store varies depending on the size of each one. Storing Photo Files on CDJPEGs, TIFFs, and RAWs are just some types of image files. When you save an image as a RAW (minimally processed), you are using one of the largest file types. While these images can be printed in higher quality, not as many can be saved to a CD. More JPEGs can be saved to a CD in a smaller file size. These images used online or printed in 4” X 6” photo size will still be decent in quality. Want to organize vacation photos and keep them separate from other images? Make one CD for travel, another for holidays, and another for school activities. You don’t always need tons of space to accommodate your storage requirements. Saving Document Files on CDFrom articles or essays you write to the ones you want to read again and again, saving these documents to a CD makes them easily accessible even out of the cloud. Save a doc or RTF and open it with a word processing program to edit again. Save PDFs of manuals, maps, and other non-editable content to reference at a later date. Creating an Album of Audio Files on CDWhether you have a library of audio recordings or music files, save them on a CD so you can easily play them on your computer or CD player. If you want to play those MP3s on your old-school stereo system, you can burn them to a CD. Save WAV and WMA audio files to a CD and listen to those interviews, readings, and other audio recordings whenever you want. CD File StorageClean off that hard drive, clear the cloud, and organize your files on a CD for future use. It may not hold as many files as a DVD-R or SD card, but it’s an easy way to organize smaller groups of photos or documents and play back music. Call Disc Hounds at 610-696-8668 with any questions about storing your files on CD. We’re happy to help you organize, transfer, or store your memories so you can enjoy them for years to come.
CD vs CD-R: A CD-R disk allows the drive to write data onto the disc the CD does not but will play the data. DAJ / Getty Images/amana images RF If you have read the HowStuffWorks article How CDs Work, you know that the basic idea behind data storage on a normal CD is simple. The surface of the CD contains one long spiral track of data. Along the track, there are flat reflective areas and non-reflective bumps. A flat reflective area represents a binary 1, while a non-reflective bump represents a binary 0. The CD drive shines a laser at the surface of the CD and can detect the reflective areas and the bumps by the amount of laser light they reflect. The drive converts the reflections into 1s and 0s to read digital data from the disc. See How CDs Work for more information. Normal CDs can not be modified -- they are read-only devices. A CD-R disc needs to allow the drive to write data onto the disc. For a CD-R disk to work, there must be a way for a laser to create a non-reflective area on the disc. A CD-R disc therefore has an extra layer that the laser can modify. This extra layer is a greenish dye. In a normal CD, you have a plastic substrate covered with a reflective aluminum or gold layer. In a CD-R, you have a plastic substrate, a dye layer and a reflective gold layer. On a new CD-R disc, the entire surface of the disc is reflective -- the laser can shine through the dye and reflect off the gold layer. When you write data to a CD-R, the writing laser (which is much more powerful than the reading laser) heats up the dye layer and changes its transparency. The change in the dye creates the equivalent of a non-reflective bump. This is a permanent change, and both CD and CD-R drives can read the modified dye as a bump later on. It turns out that the dye is fairly sensitive to light -- it has to be in order for a laser to modify it quickly. Therefore, you want to avoid exposing CD-R discs to sunlight. |