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a) DVD (also known as "Digital Versatile Disc" or "Digital Video Disc") is a popular optical disc storage media format used for data storage. Primarily uses are for movies, software, and data backup purposes, DVDs are of the same form factor as compact discs (CDs), but allow for 8 times the data storage capacity (single-layer, single-sided). i) Storage capacity: Going by the storage capacity, the DVD specifications have four disk configurations, ranging from 4.7 GB to 17 GB. It ranges from single-sided, single-layer disks that are much like traditional CD ROM disks to double-sided double-layered DVDs. Normally a DVD ROM with a minimum storage capacity can store up to the data of 7 CD ROMs. Normally the capacity of a CD ROM is only 650 MB. The capacity of DVD ROM starts from 4.4 GB, which is 7 times more than a normal CD ROM. However, this storage capacity of DVD ROM relates to single-layer storage. But with double-layer storage, the storage capacity of DVD ROM can go up to 8 GB, which is 12.5 times higher than a normal CD ROM. Furthermore, double-sided, DVD ROM drives can store 8.8 GB, 14 times greater than a CD ROM's capacity. Double-sided, dual-layer DVD-ROM drives store 15.9 GB, 25 times greater than a CD ROMs capacity. To put it differently a CD ROM can hold the entire encyclopedia, but a DVD ROM can hold the encyclopedia, the dictionary, the thesaurus, and the phone number/address of everyone in whole India with still a lot of space left! With the storage of a DVD ROM, you can see interactive multimedia programs that use hours of fullscreen video to help you see movies, play games or even learn your courses. ii) Speed of data transfer: DVD ROM scores over the CD ROM. Going by figures the minimum transfer rate of CD ROM drives is 150 KB per second. However, the minimum transfer rate of DVD ROM drives is 11.08 MB per second. The data transfer rate of DVD ROM is approximately equivalent to a 92X CD ROM. iii) Reliability: Individually though CD ROMs are very reliable and have a long shelf life yet if compared to the DVD, the DVD scores over the CDs in terms of reliability. Since DVD ROM discs are made of plastics bonded together, the discs are more rigid than CD ROM discs. Though the DVDs can also catch scratch just like CDs yet the scratches in the DVD normally do not matter as they are usually out of focus of the laser and therefore it does not affect the readability of the DVDs. In case of CDs, scratches could affect the data and could also make it useless if the scratches destroy critical tracks. Besides scratches, other factors like error correction also makes DVD much better and reliable in comparison to the CDs. Normally, in case of the DVD, the error correction is 10 times more effective than the CD error correction. Moreover the CDs normally follow RS-CIRC error correction mode, whereas DVD have RS-PC error correction. Likewise the error correction overhead in case of CD ROM is very high at 34 per cent, whereas it is only 13 per cent in case of DVD drive.