DISC SIZE, CONFIGURATION AND CAPACITY

What are the physical sizes of CD-R and CD-RW discs?
Generally, writable DVD discs come in 12 cm (120 mm) and 8 cm (80 mm) diameter sizes. The most commonly used is the larger 12 cm type which has the same physical dimension as most commercial video, audio, computer software and game console DVDs. 8 cm discs are less common and are typically used in portable consumer electronic devices such as digital video camcorders.

What configurations of writable DVD discs are available?
Currently, writable DVD discs are single-layer (SL) products which can either be single (SS) or double-sided (DS). Single-sided discs are used in everyday data and video applications while double-sided discs are more specialized (largely due to the lack of a convenient labeling surface) and are typically employed in automated storage jukeboxes and in writable DVD camcorders. In addition, DVD-RAM discs come as bare or can be enclosed in protective “cartridges”. Some types of these cartridges may be opened to allow the discs to be removed while others come permanently sealed. Be aware that not all DVD-RAM compatible drives, players and recorders accommodate cartridged discs.

DVD-RAM Disc Cartridge Configurations

Are dual-layer writable DVD discs available?
Manufacturers are developing 8.5 GB single-sided (SS) dual-layer (DL) DVD+R and DVD-R discs for release sometime in 2004 or 2005. Although they approximate dual-layer prerecorded DVD-9 discs be aware that, due to various technical issues, such writable discs may not be read compatible with some older computer DVD-ROM drives and DVD players and they will not be write-compatible with older recorders. If in doubt, check with the hardware manufacturer.

What blank writable disc capacities are available?
Manufacturers express disc capacity in terms of how much computer data a disc can contain. DVD-R (General), DVD-R (Authoring), DVD+R, DVD+RW and DVD-RAM discs come in 4.7 GB single and 9.4 GB double-sided (12 cm) and 1.46 GB single and 2.92 GB double-sided (8 cm) sizes.

This has not always been the case for DVD-RAM and DVD-R. DVD-RAM discs designed for use in early recorders (version 1.0) come in 2.6 GB single-sided and 5.2 GB double-sided (12 cm) sizes. DVD-R discs compatible with first generation recorders (version 1.0) come in 3.95 GB single-sided and 7.9 GB double-sided (12 cm) and 1.23 GB single-sided and 2.46 GB double-sided (8 cm) sizes.

Keep in mind that manufacturers quote the capacity of a writable DVD disc in decimal (base 10) rather than binary (base 2) notation so a 4.7 GB disc stores 4.7 billion bytes [4:700,000,000 bytes ÷ 1000 = 4,700,000 KB ÷ 1000 = 4,700 MB ÷ 1000 = 4.7 GB] . Expressed in binary notation (as is typical with CD-R, CD-RW and most operating systems) the same disc has a capacity of roughly 4.38 GB [4:700,000,000 bytes ÷ 1024 = 4,589,844 KB ÷ 1024 = 4,482.27 MB ÷ 1024 = 4.38 GB] .

How much information can actually be stored on writable DVD discs?
The amount of information that can be written is determined by the disc’s recording capacity as well as the physical and logical formats used.

All writable DVD formats devote the same amount of usable space to data (2,048 bytes per sector). DVD+R, DVD+RW and DVD-RAM specify the number of sectors available for user information (1.46 GB DVD+R/+RW 714,544 sectors, 4.7 GB DVD+R/+RW 2,295,104 sectors, 1.46 GB DVD-RAM 714,480 sectors, 2.6 GB DVD-RAM 1,218,960 sectors, 4.7 GB DVD-RAM 2,295,072 sectors) so disc capacity can be calculated by multiplying the user data area size by the number of disc sectors. For example, a 4.7 GB DVD+R disc: 2,048 bytes/sector x 2,295,104 sectors = 4,700,372,992 bytes. This rounds to roughly 4.7 GB (decimal notation).

DVD-R and DVD-RW, on the other hand, do not stipulate the number of sectors that are dedicated to user information but simply that a minimum capacity must be available on the disc. In the case of DVD-R (version 1.0) this is 3.95 (12 cm) and 1.23 (8 cm) billion bytes and for DVD-R (Authoring), DVD-R (General) and DVD-RW 4.7 (12 cm) and 1.46 (8 cm) billion bytes. Consequently, real world capacity can vary slightly among discs from different media manufacturers although many have informally settled on 2,298,496 sectors (4,707,319,808 bytes) for a DVD-R (General) 4.7 GB disc.

Writable DVD Disc Capacities
(Unformatted Single-Sided, Single-Layer Discs)

Be aware, however, that the logical format (UDF, FAT, HFS etc.) as well as any defect management system employed consume space otherwise available for user information. For example, DVD-RAM can dedicate as much as 184 MB (192,937,984 bytes) on a 1.46 GB disc, 126.86 MB (133,022,816 bytes) on a 2.6 GB disc and 216 MB (226,492,416 bytes) on a 4.7 GB disc for defect management while Mount Rainier formatted DVD+RW (DVD+MRW) can allocate up to 128.75 MB (135,000,000 bytes) on a 1.46 GB disc and 515.94 MB (541,000,000 bytes) on a 4.7 GB disc.

How many minutes of video can be stored on writable DVD discs?
In contrast to CD technology where Red Book audio or Video CD specifications rigidly prescribe the amount, type and quality of material a disc contains, the DVD-Video format is flexible, permitting content to be housed in different forms and levels of quality. Consequently, the number of minutes of audio and video that can be stored on a writable DVD disc varies considerably.

In terms of its basic capabilities, the DVD-Video format supports one main stream of video (MPEG-1, MPEG-2) with up to nine separate camera angles, as many as eight streams of audio (Dolby Digital, MPEG-1, MPEG-2, LPCM, DTS, SDDS), a maximum of 32 subpicture streams (graphic overlay) as well as navigation menus and other extras. Each of these occupy space so the amount of material that can be recorded depends upon the number of features incorporated, the type and degree of audio and video compression used and the capacity of the disc. For example, a single-sided 4.7 GB disc holds roughly one hour of straightforward audio and video at maximum DVD quality and a 1.46 GB disc approximately 18 minutes. At the other end of the spectrum, the same discs might accommodate as much as nine hours and three hours respectively of VHS quality material.

Not all computer video and audio encoding systems, authoring software and consumer electronics (CE) recorders offer access to all DVD-Video features or support all degrees of compression. Thus, in practice, different products offer a range of possible recording times. For example, an entry-level DVD-Video authoring software package might support only limited features and permit only one hour of recording (using as little compression as possible) to keep the quality of the final result as high as possible. Mid-range and professional hardware and software tools provide the greatest degree of freedom while consumer products generally offer the least.

Generally speaking, consumer electronics (CE) recorders have a variety of automatic or manual recording modes typically ranging from one to four hours (occasionally six to eight hours) per 4.7 GB disc while writable DVD camcorders usually offer between 20 minutes to one hour per 1.46 GB disc. Although manufacturers sometimes use language such as High Quality (HQ), Standard Play (SP), Long Play (LP) and others to describe the recording time of their products, be aware that there are no broadly accepted industry standards for the use of such terminology.

CONTINUE TO COPYING DETERRENTS
AND CONTENT PROTECTION