The bit (a portmanteau of binary digit) is a basic unit of information used in computing and digital communications.
DVD (an abbreviation of "digital video disc" or "digital versatile disc") is a digital optical disc storage format invented and developed by Philips and Sony in 1995.
DVD recordable and DVD rewritable refer to part of optical disc recording technologies.
DVD+R DL (DL stands for Double Layer) also called DVD+R9, is a derivative of the DVD+R format created by the DVD+RW Alliance.
DVD-R DL (DL stands for Dual Layer), also called DVD-R9, is a derivative of the DVD-R format standard. DVD-R DL discs hold 8.5 GB by utilizing two recordable dye layers, each capable of storing a little less than the 4.7 gigabyte (GB) of a single layer disc, almost doubling the total disc capacity. Discs can be read in many DVD devices (older units are less compatible) and can only be written using DVD-R DL compatible recorders. It is part of optical disc recording technologies for digital recording to optical disc. DVD-R DL has compatibility issues with legacy DVD-ROM drives known as pickup head overrun. To avoid this issue, the two layers of the disc need to be equally recorded. But this is a contradiction with the sequential nature of the DVD recording. Thus DVD Forum under Pioneer's lead developed a technology known as Layer Jump Recording (LJR), which incrementally record smaller sections of each layer to maintain compatibility with DVD-ROM drives. DVD-R DL media has been discontinued by most manufacturers. DVD+R DL is dominating the market for dual layered media.
DVD-RAM (DVD Random Access Memory) is a disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers.
The Rainbow Books are a collection of Compact Disc format specifications.