CD ROM : Read only write once disk holds 74 minute video (682 Mb). The disk has 120 mm diameter, 1.2 mm thickness and a 15 mm (dia) hole at the centre.Disk is of polycarbonate wafer with a data access speed in between floppy and hard disk. Optical reading/writing is done by LASER. Windows 98 comes in 75 floppies, if here is no CD ROM.

DVD : Digital Versatile Disk can read using DVD ROM drive (which can play CD ROM too and is called combo drive). A single layer DVD can store 4.7 Gb while a double layer DVD can store 8.5 Gb and is 11.5 times the capacity of a CD. A double layer DVD can store 4 hour video. Label will be at the centre near the hole.