CD-ROM (pronounced "see-dee rom") stands for compact disk, read only memory. A NON-VOLATILE OPTICAL DISK STORAGE medium based on the same physical disk format as the audio Compact Disc (CD), developed by Philips and Sony. A CD-ROM actually looks just like the CDs we play music with. To use one with your computer, you need a CD-ROM player, also called a CD-ROM reader. A CD-ROM can hold up to about 600 megabytes of information, which is the equivalent of about 700 regular floppy disks. There are CD-ROMs that hold the entire works of Shakespeare, complete dictionaries, histories, images of the works in the Louvre, etc., etc., ete. You can search the CD for the particular information you want to work with, copy it, then paste it into your own documents on your hard disk to do with what you will. You can only read from a CD-ROM, though-you can't store information onto it. The biggest complaint about CD-ROMs is that they are relatively slow.
How CDROM Work?
A CD disc inserted into a CDROM drive is spun by a motor at a varying rate. This allows the data to be read at a constant speed, regardless of whether that data is located way out on the edge of the disk, or towards the center.
A tiny laser inside the drive focuses on the spinning disc. The laser beam strikes a reflective aluminum inner surface covered with indentations (called pits) and bumps (called lands). Light is reflected back to an optical reading head. light striking a pit reflects less light than does light striking a land. A prism bends the reflected light to a photo detector, which in turn measures the intensity of the reflected light and converts it into electrical pulses that are sent back to the CPU for processing.