3.3 What are the sizes and capacities of DVD?
Description
This article is from the DVD Formats FAQ, by jtfrog@usa.net (Jim Taylor) with numerous contributions by others.
3.3 What are the sizes and capacities of DVD?
There are many variations on the DVD theme. There are two physical sizes:
12 cm (4.7 inches) and 8 cm (3.1 inches), both 1.2 mm thick. These are the
same form factors as CD. A DVD disc can be single-sided or double-sided.
Each side can have one or two layers of data. The amount of video a disc
can hold depends on how much audio accompanies it and how heavily the video
and audio are compressed. The oft-quoted figure of 133 minutes is
apocryphal: a DVD with only one audio track easily holds over 160 minutes,
and a single layer can actually hold up to 9 hours of video and audio if
it's compressed to VHS quality.
At a rough average rate of 4.7 Mbps (3.5 Mbps for video, 1.2 Mbps for three
5.1-channel soundtracks), a single-layer DVD can hold a little over two
hours. A two-hour movie with three soundtracks can average 5.2 Mbps. A
dual-layer disc can hold a two-hour movie at an average of 9.5 Mbps (very
close to the 10.08 Mbps limit).
A DVD-Video disc containing mostly audio can play for 13 hours (24 hours
with dual layers) using 48/16 PCM (slightly better than CD quality). It can
play 160 hours of audio (or a whopping 295 hours with dual layers) using
Dolby Digital 64 kbps compression of monophonic audio, which is perfect for
audio books.
Capacities of DVD:
For reference, a CD-ROM holds about 650 megabytes, which is 0.64 gigabytes
or 0.68 billion bytes. In the list below, SS/DS means single-/double-sided,
SL/DL/ML means single-/dual-/mixed-layer (mixed means single layer on one
side, double layer on the other side), gig means gigabytes (2^30), G means
billions of bytes (10^9). See note about giga vs. billion in section 7.2.
* DVD-5 (12cm, SS/SL): 4.38 gig (4.7 G) of data, over 2 hours of video
* DVD-9 (12cm, SS/DL): 7.95 gig (8.5 G), about 4 hours
* DVD-10 (12cm, DS/SL): 8.75 gig (9.4 G), about 4.5 hours
* DVD-14 (12cm, DS/ML): 12.33 gig (13.24 G), about 6.5 hours
* DVD-18 (12cm, DS/DL): 15.90 gig (17 G), over 8 hours
* DVD-1 (8cm, SS/SL): 1.36 gig (1.4 G), about half an hour
* DVD-2 (8cm, SS/DL): 2.48 gig (2.7 G), about 1.3 hours
* DVD-3 (8cm, DS/SL): 2.72 gig (2.9 G), about 1.4 hours
* DVD-4 (8cm, DS/DL): 4.95 gig (5.3 G), about 2.5 hours
* DVD-R (12cm, SS/SL): 3.68 gig (3.95 G)
* DVD-R (12cm, DS/SL): 7.38 gig (7.9 G)
* DVD-R (8cm, SS/SL): 1.15 gig (1.23 G)
* DVD-R (8cm, DS/SL): 2.29 gig (2.46 G)
* DVD-RAM (12cm, SS/SL): 2.40 gig (2.58 G)
* DVD-RAM (12cm, DS/SL): 4.80 gig (5.16 G)
Tip: It takes about two gigabytes to store one hour of average video.
The increase in capacity from CD-ROM is due to: 1) smaller pit length
(~2.08x), 2) tighter tracks (~2.16x), 3) slightly larger data area
(~1.02x), 4) more efficient channel bit modulation (~1.06x), 5) more
efficient error correction (~1.32x), 6) less sector overhead (~1.06x).
Total increase for a single layer is about 7 times a standard CD-ROM.
There's a slightly different explanation at
<http://www.mpeg.org/MPEG/DVD/General/Gain.html>.
The capacity of a dual-layer disc is slightly less than double that of a
single-layer disc. The laser has to read "through" the outer layer to the
inner layer (a distance of 20 to 70 microns). To reduce inter-layer
crosstalk, the minimum pit length of both layers is increased from .4 um to
.44 um. To compensate, the reference scanning velocity is slightly faster
-- 3.84 m/s, as opposed to 3.49 m/s for single layer discs. Longer pits,
spaced farther apart, are easier to read correctly and are less susceptible
to jitter. The increased length means fewer pits per revolution, which
results in reduced capacity per layer.
See 4.3 for details of recordable DVD (DVD-R and DVD-RAM).
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