What is a DVD?
After a long period of time dedicated to planning and development, the new format that everyone was waiting for was born. The arrival of the DVD format marked a move to a new, more advanced level in the storage and use of data, audio and video.
Originally, the acronym DVD was transcribed as digital video disc, these are large-capacity optical discs. These discs are used to store computer programs and applications, as well as full-length movies and high-quality audio. Therefore, it appeared a little later to decipher the abbreviation of DVD, as digital versatile disc, that is, a universal digital disc, is more logical.
On the outside, DVD discs look like ordinary CD-ROM discs. However, the DVD has much more possibilities. DVD discs can store 26 times more data than a regular CD-ROM. With physical size and a look similar to that of a regular CD or CD-ROM, DVD discs have been a huge leap in information storage capacity, compared to their predecessor, which contains 650 MB of data. The standard single-layer one-way DVD disc can store 4.7 GB of data. But this is not the limit: DVDs can be manufactured with a double-layer standard, which allows you to increase the data storage capacity on one side up to 8.5 GB. In addition, DVD discs can be double-sided, which increases the capacity of a single disc to 17 GB. Unfortunately, to count a DVD disc, you will have to buy a new device, but this new hardware will perfectly read your old CD-ROMs and audio CDs. What does all this mean for us by the large capacity of the new units? This means that we have really unlimited opportunities to learn and entertain, to watch videos with amazing digital images and sound quality. The DVD provides a sharper and higher quality image than the laser dis (LD) and richer sound than the CD. In addition, the DVD gives you a choice. You can choose from which angle to view the movie scene, since the same scene is shot from different angles of the camera position. Thanks to this, the same film can be seen, for example, with or without scenes of violence, and the plot of the same film can change strangely. And almost all this is already on sale! Next, let’s take a closer look at the technology that offers us so many possibilities.
DVD device basics
Like CD-ROMs, DVD discs store data, due to notches placed along the spiral tracks on a reflective metal surface covered with plastic. Used in DVD players, the laser flows along the tracks in notches, and the reflected beam is interpreted by the receiving device as one or zero.
The basic requirement, in the development of the DVD, was simple: increase the capacity of the stored data, placing as many notches as possible along the tracks on the disc, while the production technology should be economical.
The result of the research was the development of a higher frequency semiconductor laser with a smaller wavelength, which allowed the use of smaller notches.
While the laser on a conventional CD-ROM device has a wavelength of 780 nanometers (nm), DVD devices use a 650 nm or 635 nm laser, allowing the beam to cover twice the notches on a single track and twice the tracks located on a single etched surface.
Other innovations include a new industry format, more robust error correction code, and better channel modulation.
Taken together, these improvements further increase the write density of data by one and a half times. Strict production requirements and a slightly large recording area, have become the last obstacle in the development of the DVD, so the capacity of the data hosted on the disc is limited to 4.7 GB. But it turned out that it was not the limit.
To burn video and audio to DVD, a very sophisticated data compression technology called MPEG-2 is used. MPEG-2 is the next generation of the audio and video data compression (compression) standard, which offers the ability to place large amounts of information in a smaller space.
The MPEG compression standard is developed by Moving Picture Experts Group-MPEG. MPEG is the standard for compressing audio and video files into a format that is more convenient for downloading or forwarding, for example via the Internet. According to the MPEG-1 standard, video and audio streams are transmitted at 150 kilobytes per second, at the same rate as a single-speed CD-ROM player, and are controlled by sampling video keyframes and filling only areas that change between frames. Unfortunately, MPEG-1 offers lower video image quality than video broadcast through the television standard.
MPEG-2 compression radically changes things. More than 97% of the digital data representing the video signal is duplicated, i.e. redundant and can be compressed without compromising image quality. The MPEG-2 algorithm analyzes the video image for repetitions called redundancy. As a result of the redundancy removal process, a higher MPEG-2 video image is provided at lower data transfer rates. For this reason, modern means of providing video programs, such as digital satellite and DVD systems, use the MPEG-2 standard.
Multiple DVD surfaces
Most DVDs have a capacity of 4.7 GB. The use of density doubling schemes and their combination, allows you to have larger capacity units: from 8.5 GB and 9.4 GB to 17 GB.
There are the following structural types of DVDs:
Single Side / single Layer (single Side / single Layer) – this is the simplest structure of a DVD disc. This disk can hold up to 4.7 GB of data. By the way, this capacity is 7 times the capacity of an ordinary audio CD and a CD-ROM disc.
Single side / double layer (single side / double layer): this type of disk has two layers of data, one of which is translucent. Both layers are read on one side and can hold 8.5 GB of data, which is 3.5 GB more than a single-layer/single-sided drive.
Double side / single layer: this disk contains 9.4 GB of data (4.7 GB on each side). It is not difficult to note that the capacity of this double disc / DVD one-sided. Meanwhile, due to the fact that the data is on two sides, you will have to flip the disk or use a device that can read data from both sides of the disk by itself.
Double side / double layer: the structure of this disk can accommodate up to 17 GB of data (8.5 GB on each side).
Note that all the given numbers correspond to the specified capacity in millions of bytes; if you run the round according to another method, taking as a basis 1KB=1024 bytes, instead of 1000 bytes, you will get other numbers: 4.38 GB, 7.95 GB, 8.75 GB and 15.9 GB, respectively.
It is not difficult to note that the easiest way to double the capacity is to use double-sided disks. Manufacturers can make 0.6 mm thick DVD discs, which is half the thickness of a standard CD disc. This allows you to connect two disks backwards and get a capacity of 9.4 GB.
With another technology, a second layer is created to accommodate the data, which allows you to increase the capacity of one side of the disk. The first layer becomes translucent, so the laser beam can pass through it and be reflected from the second layer. In this scheme, 8.5 GB of data can be placed on each side of the cock.
If you stack double-layer disks with opposite sides, you get a very decent capacity of 17 GB.
Transmission speed and access time
Existing DVD drives have slightly slower disc speeds, compared to legacy CD-ROM drives with 3 times the speed. However, due to the denser location of the data on the DVD, its transfer rate corresponds to 9 times the transfer rate of CD-ROM drives, which in figures corresponds to a transfer of about 1.3 MB / s.
The salt is that DVD video flows at about 9 times the speed, while CD video programs are usually designed for 2 or 4 times the speed (that’s why there is no noticeable improvement in the quality of video playback when using the X24 speed CD drive). Due to the transfer of video data in 2.25-4.5 times faster, the video footage displayed by the DVD player has such a quality that, compared to it, the video from the CD-ROM player resembles a flickering image in an old cinema. And in fact, if you run the same movie with VideoCD, VHS or DVD, the difference in quality will be noticeable to the naked eye, and the DVD definitely wins. In addition, on a DVD monitor, the movie looks better than on a TV.
Now there are already second-generation DVD players on the market, which already have a speed of 2 times. Although this does not affect the quality of the playing video, it will increase the speed of downloading the software from DVD-ROM.