CD-RW

Normal music CDs and CD-ROMs are made from pre-pressed discs and encased in plastic. The actual data is stored through pits, or tiny indentations, on the silver disc surface of the internal disc. To read the disc, the drive shines a laser onto the CD-ROM’s surface, and by interpreting the way in which the laser light is reflected from the disc it can tell whether the area under the laser is indented or not.

Thanks to sophisticated laser focusing and error detection routines, this process is pretty much ideal. However, there’s no way the laser can change the indentations of the silver disc, which in turn means there’s no way of writing new data to the disc once its been created. Thus, the technological developments to enable CD-ROMs to be written or rewritten to have necessitated changes to the disc media as well as to the read/write mechanisms in the associated CD-R and CD-RW drives.

At the start of 1997 it appeared likely that CD-R and CD-RW drives would be superseded by DVD technology almost before they had got off the ground. In the event, during that year DVD Forum members turned on each other triggering a DVD standards war and delaying product shipment. Consequently, the writable and rewritable CD formats were given a new lease of life.

For professional users, developers, small businesses, presenters, multimedia designers and home recording artists the recordable CD formats offer a range of powerful storage applications (more on storage solutions). Their big advantage over alternative removable storage technologies such as MO technology,LIMDOW and PD drive is that of CD media compatibility; CD-R and CD-RW drives can read nearly all the existing flavors of CD-ROMs and discs made by CD-R and CD-RW devices can be read on both (MultiRead-capable) CD-ROM drives and current and all future generations of DVD-ROM drive. A further advantage, itself a consequence of their wide compatibility, is the low cost of media; CD-RW media is cheap and CD-R media even cheaper. Their principal disadvantage is that there are limitations to their rewrite ability; CD-R, of course, isn’t rewritable at all and until recently CD-RW discs had to be reformatted to recover the space taken by “deleted” files when a disc becomes full, unlike the competing technologies which all offer true drag-and-drop functionality with no such limitation. Even now, however, CD-RW rewrite-ability is less than perfect, resulting in a reduction of a CD-RW disc’s storage capacity.

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