Store data but
PROBABLY perpetual greed in the human mind was the inspiration that led to the invention of CD-ROM (Compact Disk- Read Only Memory) — the greed to have more storage capacity. Today compact disks (CDs) have become an integral part of computer users’ life, spurred on further by low cost storage for distributing large quantities of information, i.e. computer programs, graphics, and databases in reliable packages.
A CD is a small plastic disk with a metallic surface on which information, especially high quality sound, is recorded whereas the CD-ROM is a non-volatile optical data storage medium using the same physical format as audio CD, readable by a computer CD-ROM drives.
CD-ROMs are digital disks from which data can be read by a special laser. The laser reads binary data as 0s and 1s by distinguishing between microscopic "lands" and "pits" dots on the surface of the disk.
CDs are easily
available in different formats like audio/video or computer CD and are
widely accepted because they are cheaper and efficient. A major
drawback is they are "read only" means once the data is
encoded onto a CD it cannot be changed.
Through ’70s, Russell continued to refine CD-ROM. The computer industry adopted this medium as a source of information storage in mid-80s.
Storing data on CD
A CD is a piece of round-shape plastic made from polycarbonate layer with a diameter of 12 cm with 1.2 mm in thickness.
Mass production of CDs is a complicated task. A master CD is used to form a layer of polycarbonate on to the other CDs, which are stamped with the "pits" and "lands" on the spiral track. Once a clear piece of polycarbonate is formed, a thin reflective aluminium layer (which is what makes the disk shine) is spitted onto the disk, covering the pits. Then a thin acrylic layer is sprayed over the aluminium to protect it.
Initially the compact disk is totally flat. The data stored on a CD is in the form of 1s and 0s, where 1s are the "pits" that represent the portion burnt by the laser onto the master CD and 0s represents "land" or flat aluminium surface. Once the laser-beam passes through the polycarbonate layer, it reflects light from the aluminium layer (the ‘pits’ reflect light differently than the ‘land’) and hits optoelectronic device that detect the change in light or change in reflectivity.
A CD is a digital storage medium and as
compared to a hard disk or a floppy drive, they are enduring but
improper care can destroy them. So always use a CD-cover or a jewel case
to sheath them.