| Most of us use CDs and DVDs almost every day, yet | | | | and mini rounds. It is best to imagine this as a road with |
| few people have any idea at all how they work. To | | | | hills and valleys. The valleys are the pits and the hills |
| make matters worse even less is known about the | | | | are the lands. When the CD laser passes over a land |
| difference between a CD-ROM and CD-R. | | | | (hill), the red light reflects back to a sensor and is |
| Understanding how different types of media work, | | | | interpreted as a one. If the laser passes over a pit |
| what they cost and the advantages of each can be | | | | (valley), the laser reflects away from the sensor |
| very valuable when deciding how to proceed with | | | | representing a zero. The incredibly small dimensions of |
| your next project. Asking for only what you're familiar | | | | the lands and pits make the spiral track on a CD |
| with may be comfortable, but isn't necessarily the best | | | | extremely long. If you could lift the data track off a CD |
| use of the technology or your budget. | | | | and stretch it out into a straight line, it would be 0.5 |
| First we will explain the difference between a | | | | microns wide and almost 3.5 miles (5 km) long. |
| CD-ROM and a CD-R. CD-ROMs are manufactured | | | | CD-Rs do not have lands and pits like a ROM, but |
| through the process of injection molding to form data | | | | have a reflective metal layer that is on top of a special |
| with a plastic polycarbonate and is referred to as | | | | dye. When there is no information on the disc, this dye |
| replication. CD Replication is more economical to use | | | | allows light to shine through and reflect back off the |
| on larger run jobs above 500 pieces. CD-Rs are made | | | | metal. But when heated, this dye layer becomes dark |
| by using a laser to burn marks in a special dye on a | | | | and does not allow a reflection. So when a CD is |
| recordable disc and is referred to as duplication. The | | | | burned it is actually burning this dye layer in the form of |
| laser changes the form of the dye, encoding the | | | | ones and zeros, putting the data on the disc. When the |
| information into it. CD Duplication is typically used on | | | | disc is playing and the red laser is able to shine through |
| smaller job below 500 pieces. | | | | reflect back, it is interpreted as a one. If the red laser is |
| Now we will get into how both forms of media actually | | | | unable to reflect back due to a darkened area, it is |
| work. What must first be known is that all CDs store | | | | interpreted as a zero. So even though a CD-R does |
| information on them in a digital format, meaning data is | | | | not have "lands" and "pits" it still performs like a regular |
| read off the media as ones and zeros. On a CD-ROM | | | | disc because of the special dye layer. |
| there are millions of "lands" and "pits" representing the | | | | DVD-ROMs and DVD-Rs function similarly to their CD |
| data that span in a spiral path starting from the center | | | | cousins, but DVDs get more complicated in that they |
| going out. Because the spiral starts in the center, CDs | | | | can have multiple layers as well as data on both sides |
| can be made into smaller versions like business cards | | | | of the disc. |