While computers have been evolving at a very rapid pace, so has computer software. Software has become much more complex, and much larger too. For a while, manufacturers faced problems, because they had to use 15 or more floppy disks in order to sell their programs to the public. This made the production costs higher, while also increasing the amount of time it took for a program to install.

The CD-ROM was introduced, storing up to 700 MB of information, which is more data than 400 standard floppy disks can hold. Moreover, one CD only costs less than $1 US to produce. With reduced costs and higher performance, computer industry was in good shape from a storage standpoint. The CD gave software all of the storage and performance they needed, for a while.

As programs kept advancing further, they started to take up even more space. At this time, for many programs, one CD is not enough. Some professional programs and games are spanning 5 or more discs. As we speak, CDs are becoming a less efficient way to store data. This is why we are slowly migrating to DVD media. Most people would recognize DVDs as the next generation of media for high-quality movies for the home. What most people do not know is that a DVD can also be used to store computer data. In fact, it can store more than 15GB of data, which is more data that 20 CDs can hold. Even though DVDs can store much more data than CDs, the two technologies are almost identical.

As you can see, DVD-ROM discs are very reflective.

While you are reading on how the CD-ROM Drive works, remember that DVD Drives work almost the same way. So much of the information under this heading also applies for DVD-ROM Drives (DVD-unique information is covered lower down on this page).

The CD-ROM is very simple. There is a reflective surface, with indented parts which are not reflective. When a laser is fired at the reflective surface, it bounces back and gets picked up as a binary 1. Otherwise, if the laser is fired at the non-reflective part, it is not bounced back, and this indicates a binary 0. Here is a Flash presentation to show you how the binary 1 and 0 are picked up by the CD-ROM. Press the button marked "1" to see how a binary 1 is read. Press the button marked "0" to see how a binary 0 is read.

Full Screen

As you can see, the CD-ROM has a very simple mechanism to read the data from a Compact Disc.

Although the DVDs are closely related to CDs, there are a few differences between the two types of media. The first difference is that they can store more data. One way that this is achieved is by making the pieces of data more tightly packed. There are also two other ways that allow special DVD Discs to store 2X or even 4X as much data as a regular DVD Disc. DVD Discs can be made double-sided, as well as double-layered. Either of these two gives the DVD twice as much storage capacity, but when a DVD is made double-layered as well as double-sided, it allows fore 4X as much data. Here are some illustrations to show you what each variation of a DVD Disc would look up-close:

The typical DVD Disc, able to hold roughly 4.5 GB of data. The light grey represents plastic. The dark grey represents aluminium, while the green indicates acrylic plastic, and the black represents the label on the top. The laser can go through the plastic, but when it gets to the aluminium, it either reflects or disperses depending on the reflectiveness of the aluminium surface.

A double-layered DVD Disc. The inside layer is still coated with aluminium just like the typical DVD Disc. The difference is that there is an outer layer, which is made from a semi-reflective layer of gold. This layer lets the laser read the data from the outer layer when it focuses on it. It also lets the laser pass through it and read the inner layer when it refocuses. The extra layer gives the DVD Disc twice as much capacity as a typical DVD Disc.

Here is a double-sided and double-layered DVD Disc. It basically has the same qualities as the double-layered DVD Disc, except it holds data on the front and the back, allowing it to hold four times as much data as a typical DVD Disc. One negative thing about the double-sided DVD Disc is that labels cannot be printed on the whole DVD, making it harder to identify. There is usually a very small label near the middle of the DVD where the hole is located, and where no data is stored.