The CD-ROM and DVD-ROM drive are devices that read data, music and video off of a CD (compact disc) or DVD (Digital Versatile or Video Disc). The ROM part stands for "Read Only Memory", which means the disc can only be read from, but not written to. More commonly today, CDs and DVDs can be both read and written to. Drives are typically labeled DVD-RW, indicating the drive is capable of reading (R) and writing (W).
The CD replaced the floppy disk as the medium of choice for storage of tranportable data. When you purchase software today, it is stored on CDs. The DVD has even greater capacity and is supplanting the CD. Breakthroughs with high defintion technology is increasing the capacity of DVDs even further.
A CD or DVD is spun at high speed inside the drive while a laser is directed at the surface to read or write data. The drive speed is referenced as 12X or 12 speed (or any other number). This simply means that it spins the CD that many times faster than the original industry specification. So, a 48X CD-ROM spins the CD up to 48 times faster than the original specification. Faster is better. The speeds of a read-write drive are expressed like this, 4X 4X 32X. This means it can write to the disc up to 4 times the spec speed, rewrite the disc up to 4 times spec speed and read the disc up to 32 times the spec speed.