| Vocademy |
The Digital Video Disk (also called Digital Versatile Disk) was developed in the mid-1990s. DVDs can store more than six times as much data as a CD by using a red LED laser, which has a shorter wavelength and thus can be focused to a smaller point than infrared lasers used for CDs.
A single-layer DVD can hold 4.7 GiB of data. However, DVDs can have two data layers, focusing the laser on the desired layer. Commercially produced video DVDs usually have two layers to hold theatrical movies. Dual-layer DVDs hold 8.5 GiB of data. Commercial DVDs with theatrical movies come with up to four layers, two per side on two-sided DVDs.
The video files on a video DVD can be easily read with a computer's DVD drive. These files are in a folder named VIDEO_TS and have a dot-VOB extension (.VOB). The largest VOB files are usually the main movie. Shorter VOB files are usually the menu or trailers (or the last file of the main movie). The video format is MPEG and can be read by any viewer that can read MPEG files.
Although a DVD is about the same thickness as a CD, a DVD consists of two thin disks sandwiched together.
With the DVD came writable DVDs and erasable writable DVDs. Like the CD-R, the DVD-R could be written to, but not erased. DVD-R was the first format released. The differences between DVD+R and DVD-R are subtle. Modern drives work with either format, but DVD+R is compatible with most DVD video players, many of which can't read DVD-R. Players and drives compatible with both formats are usually labeled "DVD±RW" to indicate their compatibility.
DVD+R comes in a double-layer version (DVD+R DL) that holds 8.5 GiB of data. Perhaps the most notable aspect of DVD+R DL is that it takes longer to record on the deeper data layer than the upper layer. This is because the writing laser has to shine through the upper layer to reach the lower layer. The beam is focused on the lower layer and, therefore, distributes its power over a wider area of the upper layer. Nevertheless, the power must be reduced to prevent the upper layer from being damaged while recording on the lower layer. Thus, the lower layer takes longer to record.
These are rewritable versions of the DVD-R and DVD+R. As with the DVD-R and DVD+R, the differences are subtle, and modern drives work with either format.
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However, the DVD+RW is better suited for on-disk video editing as it is designed for more reliable random access. The DVD+R / DVD+RW format is also compatible with most DVD video players. Many DVD video players cannot read DVD-R and DVD-RW disks.
DVD-RAM was a rewritable DVD format specially designed to work like magnetic media. No special drivers were required as with UDF-formatted disks. It only works in drives designed for its use. DVD-RAM disks are no longer manufactured.
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| Vocademy |