CD-ROM stands for compact disk read-only memory. Unlike floppy and hard disks, which use magnetic charges to represent 1s and 0s, optical disks use reflected light. On a CD-ROM disk, 1s and 0s are represented by flat areas and bumpy areas (called “pits”) on its bottom surface. The CD-ROM disk is read by a laser that projects a tiny beam of light on these areas. The amount of reflected light determines whether the area represents a 1 or a 0.
Like a commercial CD found in music stores, a CD-ROM is a “read-only” disk. Read-only means it cannot be written on or erased by the user. Thus, you as a user have access only to the data imprinted by the publisher.
A single CD-ROM disk can store 650 megabytes of data. That is equivalent to 451 floppy disks. With that much information on a single disk, the time to retrieve or access the information is very important. An important characteristic of CD-ROM drives is their access rate.
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