by Scott Rossi
Most of a CD is made of clear polycarbonate plastic. The plastic has tiny or pits molded into it. The data is arranged as a long helical string that begins in the center and spirals to the outside. The laser reads a CD from the underside of the Disc and because the distance from the surface and a pit is different, you can store binary 1s and 0s , which are the building blocks of a digital signal.
Above the polycarbonate plastic layer is a layer of aluminum. On top of that is a layer of acrylic lacquer, and then the Artwork, which is often silk-screened or offset printed directly on the acrylic lacquer. As some people remember, originally compact discs were just used for audio recordings. Later the same physical size was used for CD-ROMs to store data as well. CD-ROMs are mass produced using a process called "stamping" unlike CD-Rs or CD-RWs which are recorded or "burned" by computer users.
A DVD is much like a CD except that it can hold more data. Like a CD, a DVD is made of polycarbonate that has tiny pits in it that a laser can read. A CD holds about 640MB of data, whereas a single-sided single-layer DVD can hold 4.7GB. A single-sided double layer DVD can hold 8.5GB and a double-sided double layer DVD can hold 17GB. The reason a DVD can hold more data is because the pits are spaced closer together and it can have multiple layers. DVDs also don't use as much space for error correction as CDs do.
Most of a CD is made of clear polycarbonate plastic. The plastic has tiny or pits molded into it. The data is arranged as a long helical string that begins in the center and spirals to the outside. The laser reads a CD from the underside of the Disc and because the distance from the surface and a pit is different, you can store binary 1s and 0s , which are the building blocks of a digital signal.
Above the polycarbonate plastic layer is a layer of aluminum. On top of that is a layer of acrylic lacquer, and then the Artwork, which is often silk-screened or offset printed directly on the acrylic lacquer. As some people remember, originally compact discs were just used for audio recordings. Later the same physical size was used for CD-ROMs to store data as well. CD-ROMs are mass produced using a process called "stamping" unlike CD-Rs or CD-RWs which are recorded or "burned" by computer users.
A DVD is much like a CD except that it can hold more data. Like a CD, a DVD is made of polycarbonate that has tiny pits in it that a laser can read. A CD holds about 640MB of data, whereas a single-sided single-layer DVD can hold 4.7GB. A single-sided double layer DVD can hold 8.5GB and a double-sided double layer DVD can hold 17GB. The reason a DVD can hold more data is because the pits are spaced closer together and it can have multiple layers. DVDs also don't use as much space for error correction as CDs do.
No comments:
Post a Comment