Hello everyone and welcome back! Today's subject discusses the difference between two highly popular optical disc storage media formats. We know them better as CD (Compact Disc) and DVD (Digital Video Disc).
Background Information
CD (Compact Disc)
CDs have been commercially available since 1982 - a spinoff of LaserDisc technology that was developer a few years earlier. They remain the standard storage media for commercial audio recordings despite much better options. A standard CD has a diameter of 120 mm and a thickness of 1.2 mm. CDs are made of almost pure polycarbonate plastic and weighh approximately 16 grams. A typical CD can hold nearly 80 minutes of music or 700 GB worth of data. Today there are many formats of CD. Some of the most commonly used are CD-ROM (Read Only Memory), write-once audio and data storage CD-R, rewritable media CD-RW, Super Audio CD (SACD), Video Compact Discs (VCD), Super Video Compact Discs (SVCD), PhotoCD, PictureCD, CD-i, and Enhanced CD.
DVD (Digital Video Discc)
DVDs are primarily used for video and data storage. Most DVDs have the same dimensions as CDs, but store more than 6 times as much data. Like CDs, DVDs come in a variety of formats. DVD-ROM (Read Only Memory) can only be read, while DVD-R and DVD+R can be written to only once. DVD-RW (Rewrittable), DVD+RW, and DVD-RAM can all record and erase data multiple times. Other DVD formats include DVD-Audio (high definition audio) and HD-DVD or BlueRay.
Differences
There are relatively few differences between the CD and DVD structurally. Both are made of a polycarbonate plastic and have roughly the same physical dimensions. Despite their similarities, DVDs (depending on format) are capable of more than 6 times the storage capacity of their CD counterpart. Both CDs and DVDs use a series of "pits" created and read by a laser. These pits represent the binary data of what's being stored on the CD or DVD. Maybe it's your favorite Top 40 song or your kid's overdue homework assignment. You get the idea. The more pits you can create on a disc, the greater amount of information that can be stored on the disc. DVD accomplishes its dominance over CD by allowing several times the number of pits to be jam packed on the disc. DVDs also allow for multi-layering. Multi-layering is like sandwiching two discs together; thereby, giving you more surface area to lay down pits.
The Future
The replacement for CDs and DVDs may be something out of a Star Trek movie. Holographic storage overcomes the limitations of CDs and DVDs by recording information throughout the volume of the medium and is capable of recording multiple pieces of information in the same area using different angles and colors of light. Stay tuned for more information on halographic storage!
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