Before you start
Objectives: Learn what is DVD, existing versions of DVD, and which technologies are used to create DVDs.
Prerequisites: no prerequisites.
Key terms: disk, data, dvd-r, cd, dvd-rw, video, speed, drive, lase, single, hold, rw, digital, layer, read
Compared to CD, DVD is a newer generation of optical disk storage technology. DVD is an optical media standard that can hold large amount of computer data, video, audio, and still photos. Dimensions of a typical DVD disk are the same as a CD. DVD stands for Digital Versatile Disk, but we will often hear that it means Digital Video Disk. By using Digital Video Disk we limit it to just video so it’s better to use Digital Versatile Disk. As we said, DVD can contain much more data than CD. That’s because tracks, pits and lands on a DVD are smaller then those on a CD. The track on a CD is much wider than a track on a DVD. This allows the DVD to store a lot more data than a CD, however it also causes some problems. A CD had a lot of room for errors, but with DVD that laser has to be very precisely aimed. Any unbalance can cause problems in a way that it causes the laser to miss the right track.
Types of DVDs
Unlike CDs, which contain data only on a single side, DVDs can contain data on both sides of the disc. A DVD with a single side of data can hold about 4.7 GB. A double sided disc can hold about 9.4 GB. There are also versions of DVDs which can store data in two different layers on the same side. The outer layer is semi-transparent and allows the laser to read data from the inner layer. Dual layer discs can hold up to 8.5 GB of data. Double sided, dual layer disc are possible and can hold up to 17 GB. but they are really rare. Most newer drives can read both single and dual layer discs. When it comes to speed, DVD use a multiple of 1.35 MBps (1x = 1.35 MBps). A single drive might have multiple speed ratings based on the the operation being performed (record, rewrite, or read), and the DVD format supported (such as DVD-R or DVD-RW). When multiple numbers are listed together, the first number indicates the record speed, the second number the rewrite speed, and the last number the read speed. If the drive does not perform rewrite functions, the middle number will be omitted. For example, the speed rating might be: 48x (CD) / 16x (DVD) 48x (CD) / 24x (DVD±R) / 12x (DVD±R DL) 32x (CD) / 6x (DVD-RW) / 8x (DVD+RW) / 12x (DVD-RAM). Notice that that the highest number is the read speed and the lowest number is the rewrite speed.
DVD video disk allows us to store over two hours of high quality digital video on a single layer, single sided DVD disk. DVD video supports different aspect ratios. It supports both of a typical television set 4:3 ratio, and HDTV which uses a 16:9 aspect ratio. DVD video also supports up to eight different tracks of digital audio, which allows us to have multiple languages, commentaries etcetera. In addition we can have up to 32 different subtitle tracks.
A DVD ROM is a PC version of a DVD disk. Basically it’s like a big CD ROM. CD ROM holds from 650 to 700 megabytes of data, but the DVD can hold 4.7 gigabytes of data.
DVD drives are also rated according to their speed. We have a 1X, 2X, 4X, 8X, 10X, etcetera, With a DVD a 1X drive transfers data at 11 megabits per second, a 2X drive transfers data at 22 megabits per second, a 3X drive transfers data at 33 megabits per second and so on. Now, just like we have recordable CDs, we also have recordable DVDs.
Note that this is not a DVD minus R, it’s just a DVD R or a DVD dash R. A DVD-R works in basically the same way as a CD-R. The bottom of the DVD-R disk is coded with an organic dye, just like a CD-R disk. In order to write data to it we have a high power laser in the DVD-R drive that fires and hits the bottom surface of the DVD-R disk. When that happens it creates a dark spot which functions like a pit on a CD or DVD, which doesn’t reflect light. That way we have reflective areas and non reflective areas. A DVD-R is compatible with most DVD drives in PCs as well as most DVD players. Just like a DVD-ROM a DVD-R holds 4.7 gigabytes of data.
There are actually two different types of DVD-R. We have an authoring version and a general version. The general version of a DVD-R is sometimes referred to as a DVD-RG. It is intended for home use and it writes with a lower intensity, lower quality 650 nanometer laser. A DVD-R Authoring or DVD-RA is intended for professional DVD development and uses a very high quality, high intensity 635 nanometer laser. Now DVD-RA disks are not writable in DVD-RG recorders. However, DVD-RA and DVD-RG disks are both playable in most DVD players and are readable in most VC/DVD drives.
Just like a CD-RW a DVD-RW uses a crystalline surface on the bottom of the DVD. When a laser hits it, it causes a crystal to form, which then reflects light. DVD-RW is playable in most DVD drives and most players. Its capacity is also about 4.7 gigabytes. Typically a DVD-RW disk can be written and rewritten about 1,000 times, depending on the quality of the disk.
DVD+R and DVD+RW
Just like a DVD-RW, a DVD+RW uses a crystalline coating on the bottom of the disk. When a high intensity laser hits it, it creates a crystal which reflects. The areas that the laser doesn’t hit doesn’t reflect. The capacity of a DVD+RW is 4.7 gigabytes, just like a DVD-RW disk. A write-once version of the DVD+RW is called DVD+R. Just like a DVD-R or a CD-R, DVD+R disk uses dye on the bottom of the disk. The difference between the DVD-R and the DVD+R and with DVD-RW and the DVD+RW is that there’s a higher degree of compatibility with DVD-R and DVD-RW, but today most DVD drives can read and write either format. Older drives or older DVD players might only support DVD-R. The advantage of DVD+R and DVD+RW is the feature of editing right on the disk. Also, DVD+R is generally considered more robust.
There are four basic interfaces that are used for CD and DVD drives. Those are IDE, SATA, SCSI, USB and Firewire. If we want an external drive then we need to look at USB or Firewire.
DVD is an optical media standard that can hold large amount of computer data, video, audio, and still photos. Tracks, pits and lands on a DVD are smaller then those on a CD. A DVD with a single side of data can hold about 4.7 GB. DVDs use a multiple of 1.35 MBps (1x = 1.35 MBps) to determine the speed. DVD video disk allows us to store over two hours of high quality digital video on a single layer, single sided DVD disk. The bottom of the DVD-R disk is coded with an organic dye. Just like a CD-RW a DVD-RW uses a crystalline surface on the bottom of the DVD. DVD+R and DVD+RW are generally considered more robust then DVD-R and DVD-RW.