In: Categories » Computers and technology » Storage devices » Short presentation of DVD Capacity (Sides and Layers)
| Four main types of DVDs are available, categorized by whether they are single- or double-sided, and single- or dual-layered. They are designated as follows:
Dual-layer discs can have the layers recorded in two ways: either OTP or parallel track path (PTP). OTP minimizes the time needed to switch from one layer to the other when reading the disc. When reaching the inside of the disc (end of Layer 0), the laser pickup remains in the same locationit merely moves toward the disc slightly to focus on Layer 1. When written in OTP mode, the lead-out zone toward the outer part of the disc is called a middle zone instead. Discs written in PTP have both spiral layers written (and read) from the inside out. When changing from Layer 0 to Layer 1, PTP discs require the laser pickup to move from the outside (end of the first layer) back to the inside (start of the second layer), as well as for the focus of the laser to change. Virtually all discs are written in OTP mode to make the layer change quicker. To allow the layers to be read more easily even though they are on top of one another, discs written in PTP mode have the spiral direction changed from one layer to the other. Layer 0 has a spiral winding clockwise (which is read counterclockwise), whereas Layer 1 has a spiral winding counterclockwise. This typically requires that the drive spin the disc in the opposite direction to read that layer, but with OTP the spiral is read from the outside in on the second layer. So Layer 0 spirals from the inside out, and Layer 1 spirals from the outside in. DVDs store up to 4.7GB17.1 GB, depending on the type
As you might notice, the capacity of dual-layer discs is slightly less than twice of single-layer discs, even though the layers take up the same space on the discs (the spiral tracks are the same length). This was done intentionally to improve the readability of both layers in a dual-layer configuration. To do this, the bit cell spacing was slightly increased, which increases the length of each pit and land. When reading a dual-layer disc, the drive spins slightly faster to compensate, resulting in the same data rate. However, because the distance on the track is covered more quickly, less overall data can be stored. Besides the standard four capacities listed here, a double-sided disc with one layer on one side and two layers on the other can also be produced. This would be called a DVD-14 and have a capacity of 13.2GB, or about 6 hours and 15 minutes of MPEG-2 video. Additionally, 80mm discs, which store less data in each configuration than the standard 120mm discs, can be produced. Because of the manufacturing difficulties and the extra expense of double-sided discsand the fact that they must be ejected and flipped to play both sidesmost DVDs are configured as either a DVD-5 (single-sided, single-layer) or a DVD-9 (single-sided, dual-layer), which allows up to 8.5GB of data or 242 minutes of uninterrupted MPEG-2 video to be played. The 133-minute capacity of DVD-5 video discs accommodates 95% or more of the movies ever made.
 |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
legal disclaimer
1) Our website is not responsible for the information contained by this article as well for any and all copyright infringements by authors and writers. E-articles is a free information resource. If you suspect this article for any copyright infringements, please read the Terms of service and contact us to investigate the problem.
2) The E-articles directory team is not responsible for inaccuracies, falsehoods, or any other types of misinformation this tutorial may contain and will not be liable for any loss or damage suffered by a user through the user's reliance on the information gained here. Please read the Terms of service
Useful tools and features
If you like this article (tutorial), please link to it from your web page using the information above. Linking to this page, this is the only way to help us improve our service, the same time providing your visitors with a way to improve their online experience.
related articles
Subcode bytes enable the drive to find songs (which are confusingly also called tracks) along the spiral track and also contain or convey additional information about the disc in general. The subcode bytes are stored as 1 byte per frame, which results in 98 subcode bytes for each sector. Two of these bytes are used as start block and end block markers, leaving 96 bytes of subcode information. These are then divided into eight 12-byte subcode blocks, each of which is assigned a letter designation PW. Each subcode channel can hol...
2. High Capacity Magnetic Storage Devices
High-capacity removable media drives are an ever-shrinking category. With competition at the low end (1GB and under capacities) from USB flash memory keychain drives and at higher capacities from external mini-hard disks (4GB and up), rewritable DVD (8.5GB), and larger USB and FireWire hard disks (20GB and up), there are only two current product families, both from Iomega: Zip. Flexible media, with capacities of 100MB, 250MB, and 750MB REV. Rigid media, with capacity of 35GB (native...
3. Handling CD Read Errors
Handling errors when reading a disc was a big part of the original Red Book CD standard. CDs use parity and interleaving techniques called cross-interleave Reed-Solomon code (CIRC) to minimize the effects of errors on the disk. This works at the frame level. When being stored, the 24 data bytes in each frame are first run through a Reed-Solomon encoder to produce a 4-byte parity code called "Q" parity, which then is added to the 24 data bytes. The resulting 28 bytes are then run though another encoder that uses a different scheme...
4. Floppy Drive Types
As distinct from diskette types and formats, six drive types have been installed in PC-compatible systems: 5.25-inch 160/180 KB (SSDD) Single-Sided, Double-Density(SSDD) was the standard FDD in very early PC-class systems. These drives read and write only SSDD diskettes. 5.25-inch 320/360 KB (DSDD) Double-Sided, Double-Density(DSDD) was the standard FDD in PC-class systems, and was often found as a second FDD in early AT and 386 systems. The...
5. How to choose a Tape Backup Drive
Choosing a tape backup drive can be a simple job if you need to back up a single standalone system with a relatively small hard drive. The decision becomes more complex if the system has a larger hard drive or if you must back up a desktop system as well as a laptop. Choosing a tape backup drive type can be an even more complex program if you must back up a network server's hard drives and perhaps even back up the workstations from the server. As you ponder which backup tape drive you should select, consider the following facto...
6. DVD Copy Protection
DVD video discs employ several levels of protection that are mainly controlled by the DVD Copy Control Association (DVD CCA) and a third-party company called Macrovision. This protection typically applies only to DVD-Video discs, not DVD-ROM software. So, for example, copy protection might affect your ability to make backup copies of The Matrix, but it won't affect a DVD encyclopedia or other software application distributed on DVD-ROM discs. Note that every one of these protection systems has been broken, so with a lit...
7. How to Manually Resolve Motherboard Conflicts
In the past, the only way to resolve conflicts manually was to take the cover off your system and start changing switches or jumper settings on the adapter cards. Fortunately, this is a bit easier with plug-and-play because all the configuration is done via the Device Manager software included in the operating system. Although some early plug-and-play cards also had jumper switches or setup options to enable them to be configured manually, this feature was found primarily on ISA PnP-compatible cards. Be sure you write down or print o...
8. Hard Drive Advancements
In 1957, Cyril Northcote Parkinson published his famous compilation of essays titled Parkinson's Law, which begins with the statement, "Work expands so as to fill the time available for its completion." A corollary of Parkinson's most famous "law" can be applied to hard drives: "Data expands so as to fill the space available for its storage." This, of course, means that no matter how big a drive you get, you will find a way to fill it. I know that I have lived by that dictum since purchasing my first hard disk drive more than 2...
9. How Magnetic Fields Are Used to Store Data
All magnetic storage devices read and write data by using electromagnetism. This basic principle of physics states that as an electric current flows through a conductor (wire), a magnetic field is generated around the conductor. Note that electrons actually flow from negative to positive as shown in the figure, although we normally think of current flowing in the other direction Electromagnetism was discovered in 1819 by Danish physicist Hans Christian Oersted, when he found that a compass needle would deflect away from p...