DVD Tutorial
DVD, which is once stood for Digital Video Disc and later Digital Versatile Disc, is now just "DVD". It is no
longer an acronym that it once was. DVD is today's premiere format for video, audio, and data storage
The Disc
As a disc, DVD looks very much like the CD. Both are shiny discs that are 4 3/4 inches (12.0 cm) in diameter.
Both are optical formats containing digital information. This means a laser pickup is used to read the digital
data encoded on the disc. But that's where the similarities end.
DVD is actually a family of physical and application formats. As far as the physical format, DVD can hold
anywhere from seven times to over 25 times the digital data on a CD, depending on the the disc's
construction. Additionally, the DVD may be used for video, audio, or data storage applications as a DVD-
Video, DVD-Audio, or DVD-ROM application format, respectively.
The Physical Format
There are three reasons for DVD's greater data capacity, smaller pit size, tighter track spacing, and multiple
layer capability
Smaller Pit Size. DVDs have smaller pit size than CDs. Pits are the slight depressions or dimples on the
surface of the disc that allow the laser pickup to distinguish between the digital 1's and 0's.
Tighter Track Spacing. DVDs also feature tighter track spacing (i.e., track pitch) between the spirals of pits.
In order for a DVD player to read the smaller pit size and tighter track spacing of the DVD format, a different
type of laser with a smaller beam of light is required. (This is one of the major reasons why CD players
cannot read DVDs, while DVD players are capable of reading Audio CDs.)
Multiple Layer Capability. Finally, DVDs may have up to 4 layers of information, with two layers on each
side. To read information on the second layer (on the same side), the laser focuses deeper into the DVD and
reads the pits on the second layer. When the laser switches from one layer to another layer, it is referred to
as the "layer switch" or the "RSDL (reverse spiral dual layer) switch". To read information from the other side
of the DVD, almost all DVD players require the user to manually flip the disc.
A comparison of a CD's pit size and track spacing vs. that of a DVD (picture courtesy of Crutchfield.com)
DVD speed is the maximum speed at which the drive reads data from a DVD disc. The read speed determines
the data transfer rate. For example a 2X drive provides a 2.7MB/sec maximum transfer rate; a 4.8X drive
provides a 6.536MB/sec rate; and a 5X drive provides a 6.74MB/sec rate.
DVD drive "X" speeds should not be directly compared to CD drive speeds because information on DVDs is
much more compact than on CDs. Therefore, DVD-ROM drives spin slower, allowing data transfer to be much
faster. A 2x DVD read speed is roughly equivalent to a 16x rate on a CD.
Two other speeds to consider in a CD/DVD drive are the Access Time and the Transfer Rate. Access Time is
measured in milliseconds (ms) and indicates the amount of time that elapses from the time a request is made
to the drive until the data begins to be read. Transfer Rate is measured per second and refers to how quickly
data can be read from and sent to the drive. The Transfer Rate is most important when copying a large
amount of data to or from the drive.
What are region codes?
Movie studios use region codes on DVDs to thwart unauthorized copying, and to control the release dates of
DVD movies. The actual region code is stored in one byte on the DVD. The DVD player or drive has a region
code in its firmware. Personal computer DVD-ROM players often have the code in the software or in the
MPEG-2 decoder.
For the player or drive to play the movie, the two codes must match. The code is also printed on the back of
a DVD package, superimposed on a small image of the globe. If you have a DVD that was made for release in
Asia, you won't be able to play it on a DVD player intended for use in Australia.
Based on DVD's dual-layer and double-sided options, there are four disc construction
formats:
1. Single-sided, single-layered
3. Single-sided, dual-layered
2. Double-sided, single-layered
4. Double-sided, dual-layered
1. Single-Sided, Single-Layered. Also known as DVD-5, this simplest construction format holds 4.7 Gigabytes
(GBytes) of digital data. The "5" in "DVD-5" signifies the nearly 5 GBytes worth of data capacity. Compared to
650 Megabytes (MB) of data on CD, the basic DVD-5 has over seven times the data capacity of that of a CD.
That's enough digital information for approximately two hours of digital video and audio for DVD-Video, or 74
minutes of high resolution music for DVD-Audio.
2. Single-Sided, Dual-Layered. The DVD-9 construction holds about 8.5 GBytes. DVD-9s do not require
manual flipping: the DVD player automatically switches to the second layer in a fraction of a second, by re-
focusing the laser pickup on the deeper second layer. This capability allows for uninterrupted playback of
long movies up to four hours! Frequently, DVD-9 is used to put a movie and its rich set of bonus materials on
the same DVD-Video disc, or its optional DTS Surround Sound track.
3. Double-Sided, Single-Layered. Known as DVD-10, this construction features a capacity of 9.4 GBytes of
data. DVD-10s are commonly used to put a widescreen version of the movie on one side, and a full frame
version of the same movie on the other side. Almost all DVD players require you to manually flip the DVD,
that's why the DVD-10 is called the "flipper" disc. (There are a few DVD players that can perform the side
flipping automatically.)
4. Double-Sided, Dual-Layered. The DVD-18 construction can hold approximately 17 GBytes (almost 26 times
the data capacity of a CD), or about 8 hours of video and audio as a DVD-Video. Think of DVD-18 as a double-
sided DVD-9, where up to four hours of uninterrupted video and audio can be stored on one side. To access
the content on the other side of a DVD-18, you have to manually flip the DVD. To date, few titles have been
released using this construction. Content providers (e.g., movie studios) usually choose to go with two DVD-
9s than a single DVD-18 because DVD-18s cost far more to produce.
The Application Formats
Now that you understand the various physical aspects and data capacities of the DVD format, let's discuss the
various application formats of DVD: DVD-Video, DVD-Audio, and DVD-ROM. Each of these three application
formats are based on the physical specifications we just discussed.
DVD-Video. The DVD-Video format is by far the most widely known, as it is the first DVD application format
to really take off. As the name indicates, DVD-Video is principally a video and audio format used for movies,
music concert videos, and other video-based programming. This format first emerged in the spring of 1997
and is now considered mainstream, having pass the 10% milestone adoption rate in North America by late
2000. Read more about the DVD-Video application format.
DVD-Audio. The DVD-Audio format features high-resolution 2-channel stereo and multi-channel (up to 6
discrete channels of) audio. The format made its debut much later, in the summer of 2000, due to delay in
squaring away the copy protection issue. To date, DVD-Audio titles are still very few in number and have not
reach mainstream status, even though DVD-Audio/Video players are numerous and widely available. Read
more about the DVD-Audio application format.
DVD-ROM. DVD-ROM is a data storage format just like CD-ROM. DVD-ROMs can only be used in DVD-ROM
drives in computer systems. They allow for data archival and mass storage, as well as interactive and/or
web-based content.
It should be noted that a DVD disc may contain any combination of DVD-Video, DVD-Audio, and/or DVD-ROM
application content. For example, some DVD movie titles contain DVD-ROM content portion on the same disc
as the movie. This DVD-ROM content provides additional interactive and web-based content that can be
accessed when using a computer with a DVD-ROM drive. As another example, some DVD-Audio titles are
actually DVD-Audio/Video discs that actually have additional DVD-Video content that provide video-based
bonus programming such as artist interviews, music videos, or a Dolby Digital and/or DTS surround soundtrack
that can be played back by any DVD-Video player (in conjunction with a 5.1-channel surround sound home
theater system).
Before we leave this general tutorial about the DVD format, let's briefly touch on the topic of recordable DVD
formats.
What About Recordable DVD Formats?
As we mentioned before, DVD is actually a family of formats. So far we have only discussed pre-recorded
formats, those that have been manufactured with content already recorded (DVD-Video movies and DVD-
Audio music recordings). However, DVD also includes recordable formats. In fact, there are three different
recordable DVD formats:
DVD-R/RW format (with its write-once DVD-R variant and rewriteable DVD-RW variant)
DVD+R/RW format (with its write-once DVD+R variant and rewriteable DVD+RW variant)
DVD-RAM rewritable format
Each of these recordable DVD formats are slightly different. Their differences are enough to create mutually
incompatibility issues. (That is, one recordable format can not be used interchangeably with the other two
recordable formats.) And not all recordable DVD discs are 100% backwards compatible with the tens of
millions of existing DVD-Video players and computer DVD-ROM drives
DVD-R/RW Format
The DVD-R/RW format consists of the write-once DVD-R and the rewritable DVD-RW formats.
“DVD-R/RW” is shorthand for “DVD-R and DVD-RW
DVD-R comes in two flavors: “DVD-R Authoring” and “DVD-R General”.
DVD-R for Authoring is for the commercial world, where its primary application is DVD authoring (or content
generation).
DVD-R for General, as the name implies, is for consumer and home use. When you buy a DVD-R disc, be
sure to buy the DVD-R General format. DVD-R for Authoring discs will not work, as they are designed for DVD-
R Authoring devices which employ slightly shorter 625-nm wavelength lasers. Early DVD-R discs have two
capacities, 3.95 GB or 4.7 GB. Nowadays, all DVD-R discs are made with 4.7 GB capacity.
Recording works on the principle of a red laser permanently transforming a dye-recording layer on the DVD-R
disc, similar to how CD-R recording (or “burning”) works. This permanent transformation of the media is
characteristic of a write-once format. DVD-R has an expected lifespan of about 100 years. Like the DVD-Video
format, the video information is written as a single track, starting from the inner-most portion of the disc and
spiraling out to the outer edge. (We bet you didn't know that.) Since it achieves a reported better than 90%
backwards compatibility with existing DVD-Video players and computer DVD-ROM drives, DVD-R is ideal for
archiving and distributing home videos. There’s a high likelihood that the DVD-R you make would be viewable
on any DVD-Video player and computer DVD-ROM drive, but there is no 100% guarantee - it is not possible in
today’s world of recordable DVD formats.
Introduced in late 1999, DVD-RW supports 1,000 rewrite cycles with a 4.7 GB data capacity. It uses phase-
change technology, allowing video and data to be recorded incrementally as a series of sequential recording
sessions. The format also allows for a single start-to-finish disc-at-once recording session, when the disc is
finalized at the end. Finalization is a process that essentially "completes" the recording process and makes the
disc readable by playback-only devices. DVD-RW has a backwards compatibility rate of roughly 65% with
existing DVD-Video players and DVD-ROM drives. Its expected shelf life is at least 30 years.
DVD+R/RW Format
The DVD+R/RW format consists of the write-once DVD+R and the rewritable DVD+RW variants.
DVD+RW officially stands for “DVD+ReWritable Video”.
Note the previous format had a dash (“-”), while this format has a plus (“+”). In comparison with the
other formats, the DVD+R/RW format was last to be introduced.
The rewritable DVD+RW variant was introduced in late 2001, before its write-once variant was even conceived.
The write-once DVD+R variant was later announced by Philips at the 2002 Consumer Electronics Show for
introduction in mid-2002. DVD+R/RW competes directly with the DVD-R/RW format. Interestingly, DVD+R and
DVD+RW formats are not endorsed by the DVD Forum, nevertheless, the following manufacturers have
committed to this format: Sony (who also supports the DVD-R/RW format), Yamaha, Thomson, Ricoh,
Mitsubishi Chemical, Hewlett-Packard, Dell, and Microsoft. Microsoft joined the DVD+RW Alliance late, in May
2003.
So what does the DVD+R/RW format have going for it? Well, technically the DVD+R variant allows editing to be
performed until the disc is finalized. And finalizing a DVD+R disc takes about one minute, versus about 15
minutes for a DVD-R disc. Philips claims that DVD+R/RW is backwards compatible with most existing DVD-
Video players and computer DVD-ROM drives. Realistically, expect about 85% backwards compatibility for
DVD+R and about 65% backwards compatibility for DVD+RW.
DVD+R holds 4.7 GB for a single-sided disc, or 9.4 GB for a double-sided disc. Video can be recorded in High
Quality (HQ) or standard play (SP) recording mode for up to 500 lines of resolution, or in Long Play (LP) or
extended play (EP) recording mode for up to 250 lines of resolution. The DVD+R/RW formats use “lossless
linking” to maximize recording time. This works by minimizing the large blank spots caused by multiple
recording sessions. Like DVD-R, DVD+R uses a red laser to permanently transform a dye-recording layer on
the DVD+R disc for write-once recording. DVD+R has an expected lifespan of about 30-100 years and each
blank disc costs about $4 as of May 2003.
DVD+RW uses phase-change technology for multiple re-rewrites, up to 1,000 cycles. It boasts a defect
management feature and short formatting time. DVD+R/RW writes data from the inside edge spiraling out the
outer edge, just like a DVD-Video disc. The format supports recording in both constant angular velocity (CAV)
(constant rotation speed) and constant linear velocity (CLV) (constant linear track speed, with disc rotation faster
when the track being written to/read from is closer to the inner hub) modes. You should always use the CLV
mode, since CAV recordings cannot be read by DVD-Video players and computer DVD-ROM drives
DVD-RAM Format
The third recordable DVD format is DVD-RAM. It was invented by Matsushita, the parent company of
Panasonic and Technics, and was introduced in summer of 1998. The DVD-RAM format is supported by the
DVD Forum. A DVD-RAM disc looks like any other DVD, and the name DVD-RAM incorporates the letters
“DVD”. But make no mistake, DVD-RAM is in many ways not a real DVD. As the second part of its name
clearly states, it is like random access memory (RAM). The easiest way to explain the DVD-RAM format is to
think of it as a removable hard disk. DVD-RAM uses phase change dual and magneto-optic technologies for up
to 100,000 recording cycles.
A single-sided 12-cm (4.75-inch) DVD-RAM disc holds 4.7 GB, so a double-sided 12-cm DVD-RAM disc holds
9.4 GB. DVD-RAM discs also comes in a compact size of 8-cm (3-inch). This smaller version is used in DVD-
RAM camcorders from Hitachi and Panasonic. A double sided 8-cm DVD-RAM disc has a capacity of 2.8 GB,
enough for 60 minutes of high resolution video. The early version of the DVD-RAM format required a disc
cartridge (or caddy), while later models may or may not use the cartridge design. The current design allows the
disc to be removed from the cartridge housing. DVD-RAM is expected to have a lifespan of about 30 years.
DVD-RAM’s principal advantages are its removable hard disk characteristic and robustness, making it ideal for
computer data storage. Data storage is random and non-linear, meaning data can be stored in non-contiguous
blocks, much like a computer hard disk. In a video editing application, as you perform cut and insert video
editing functions with a DVD-RAM recorder, the video streams can be dynamically linked in the new order that
they’re edited, without having to re-record video streams on the disc in physical sequential order. This is the
random access feature of DVD-RAM. Additionally, DVD-RAM incorporates a defect management feature to
ensure that the video stream is recorded in a non-defective area of the disc, so content loss is minimized.
Inherent in its design, a DVD-RAM disc is incompatible with virtually all DVD players and computer DVD-ROM
drives. Only DVD-Video players made by Panasonic since 2001 are playback-compatible with DVD-RAM
discs. Such players are designated by Panasonic as “DVD-RAM compatible”. The backwards incompatibility
issue puts the DVD-RAM format at a huge disadvantage when it comes to sharing home videos and other
recordings with family and friends.
So which is the best recordable DVD format?
Well that really depends too... You didn’t think it would be that easy, did you?
For a standalone DVD recorder, we think the DVD-R/RW is the best format.
Here is why. The ability to share a recordable DVD disc with families and friends (and their ability to play it back
on their DVD-Video player or computer DVD-ROM drive) is important. Therefore, backwards compatibility with
existing DVD-Video players and computer DVD-ROM drives is essential. The write-once DVD-R format
reportedly offers a better than 90% backwards compatibility rate. If this is true, it is clearly the best format for
sharing your home video collection. In comparison, DVD+R runs a close second, with an expected backwards
compatibility rate of about 85%. DVD-RAM is a non-starter, with its radically different design optimized for
computer data storage.
Two separate formats are competing for the recordable DVD market: DVD-R/DVD-RW and DVD+RW. DVD-R
allows write once DVD burning at a speed of 2x, rewritable media is limited to 1x. DVD+RW, however, features
rewritable burning at 2.4x. DVD speeds are rated differently than CD drives; 2x on a DVD writer is equivalent to
the speed of data a 16x CD writer can burn at.
Here are relative strengths of DVD+RW over DVD-RW:
Record performance. DVD-RW drives are currently limited to 1x record speed (10 megabits/second),
whereas DVD+RW drives can write at 2.4x speed (about 25 megabits/second). Note, however, that you
can get DVD-R (write once) disks that can record at 2x speeds.
DVD+RW supports defect management; DVD-RW does not.
DVD+RW drives support both CLV (constant linear velocity) and CAV (constant angular velocity) spin
rates. The second is particularly important for PC users, as it allows for higher speed DVD and CD-ROM
reading.
DVD+RW has been adopted by Microsoft to natively support the Mount Rainier standard for drag-and-
drop, rewritable optical storage.
DVD+RW supports high-accuracy editing of 32K blocks in place, called "lossless sector linking"
DVD+RW supports variable bit-rate encoding for video, resulting in better image quality in high-motion
scenes.
There's no lead-on or lead-out times needed during write
There's no "finalize" state to creating a DVD video disc, unlike DVD-RW.
And here are some advantages of DVD-RW over DVD+RW:
Despite the goal of universal compatibility, more consumer DVD players to date will read DVD-RW disks
than DVD+RW disks "out of the box". If allowed to set the compatibility bit (as in the HP drive we
review), that number goes up. Note that newer consumer drives can read both formats.
Most mastering houses that will press consumer DVDs are set up to accept DVD-R media; some will
accept DVD-RW as well.
There's currently greater penetration and awareness of DVD-RW among authoring professionals.
Although aftermarket DVD+RW solutions exist for the Macintosh, the Macintosh can natively read and
write DVD-RW.
The good news is that there will be a single standard for next generation, high capacity recordable optical
media, known as "Blu-Ray". Those drives will probably arrive in 2004, use a blue laser and offer 30GB
capacities. Until then, our best advice is to wait for the second generation drives that offer full DVD+R support, if
you feel you need lower cost, write-once media. These should be hitting the streets in May.
What does the x stand for on 32x?
The x on 32x means that theoretically this drive is 32 times faster then the original CD-ROM drive. See our
transfer rates for exact speeds.
DRIVE SPEED TRANSFER RATE (BPS) ACCESS TIME (ms)
Single-speed (1x) 153,600 400
Double-speed (2x) 307,200 300
Triple-speed (3x) 460,800 200
Quad-speed (4x) 614,400 150
Six-speed (6x) 921,600 150
Eight-speed (8x) 1,228,800 100
Ten-speed (10x) 1,536,000 100
Twelve-speed (12x) 1,843,200 100
Sixteen-speed (16x) 2,457,600 90
Eighteen-speed (18x) 2,764,800 90
Twenty-four-speed (24x) 3,686,400 90
Thirty-two-speed (32x) 4,915,200 85
One-hundred-speed (100x) 15,360,000 80
CAV drives (12x - 24x) 1,843,200 - 3,686,400 150-90
When referring to a computer CD drive, an "x" refers to the transfer speed. For example the original 1X CD-
ROM had a speed of 153,600 BPS, this means a 24X has a BPS of 3,686,400 or 153,600 x 24. The higher the
number the faster data is going to be read from the CD drive.
There are three different types: CLV,CAV and P-CAV.
First it's important to know that, unlike hard disks, the data density on a CD is the same on every part of the
disc. This means that there is more data on the outer part of the disc then on the inside.
CLV (Constant Linear Velocity)
The data transfer rate is kept at a fixed level by changing the rotation speed.
This means you should get the number that's displayed on the box.
CAV (Constant Angular Velocity)
The drive maintains a consistent rotation speed which will result in a variable transfer rate.
If you're buying a new CD-Rom unit, it's very likely that you will only see the maximum speed the drive can
achieve.
To know what the real speed is, you have to look in the manual or on the website from the manufacturer. There
you will see two speeds: the minimum and the maximum.
The average transfer rate is (min+max)/2.
P-CAV (Partial Constant Angular Velocity)
This is a combination of CLV and CAV.
The transfer rate goes up until the drive reaches it's maximum speed (CAV). From that point the drive will slow
down and the transfer rate will be constant (CLV).
Because P-CAV drives reach their maximum speed much sooner than CAV drives, the average transfer rate
should be higher
CD-ROM drives which are over 16x will generally have max written next to it. When max is written next to the
speed or on the drive this indicates that the CD-ROM uses CAV or Constant Angular Velocity to access the data
on the CD. Originally CD-ROM drives utilized CLV or Constant Linear Velocity where the information was
obtained of the CD-ROM drive was accessed slower / faster by adjusting the speed of the motor which allows
the data to be transferred at a steady flow.
With CAV the CD rotates at a constant speed without adjusting when at a different location on the CD which
means a 32x speed CD-ROM for example will be able to access the data 32x on the outside layer however
when approaching the middle of the CD-ROM drive the access speed can decrease close to 20x.
seek time
Like latency, seek time is a measurement of the read/write performance of a disk drive. For a magnetic disk
drive, seek time is the amount of time it takes to move the read/write head from its current track to the track
where data is to be read from or written to. For a CD-ROM drive, seek time is the amount of time it takes to
position the laser beam over the portion of the CD’s single spiraling track that contains the data to be read. Seek
time is used to assess disk drive performance.
latency
Like seek time, latency is a measurement of the read/write performance of a disk drive. Latency is the time it
takes for a particular sector to pass under the read/write head of a disk after the head is positioned over the
appropriate disk track. The maximum latency for a magnetic disk is the time it takes for a complete rotation of a
disk; the average latency of a magnetic disk is half the time of a complete rotation, assuming the sectors are
requested at random. For a CD-ROM, the latency is the time it takes for a particular sector to pass under the
laser beam after the photodetector is positioned an appropriate distance from the edge of the disk.
A 7200 rpm drive has a rotational latency of 4.15 ms on average. A 4500 rpm drive has a rotational latency of
6.67 ms on average. So a 7200 rpm drive with a seek of 12.5ms has an access time that is just as fast as a
4500 rpm drive with a seek of 10.0 ms.
Iomega's marketing uses comparable CD recording speeds to demonstrate the prowess of its new Zip 750MB,
but marketing rarely lives up to reality. For our comparison, we pitted the Zip 750MB against the $220 TDK
veloCD 40x USB 2.0 CD recorder.
We used three sets of test files to measure the performance of each drive. We used Nero 5.5 as our CD
authoring application and Windows Explorer for everything else, including reading and writing to the Zip 750MB.
Test 1: Ten files totaling 644MB
Test 2: Folder containing over 5,300 files and 90 folders totaling 289MB
Test 3: Folder containing 160 .MP3s totaling 645MB.
Write tests
We tested the Zip 750MB's write performance against 12x rated CD-RW media. The results are in MB/s, with
higher being better.
CD-RW VS Zip 750MB Write Test: results in MB/s, higher is better Test 1 Test 2 Test 3
Zip 750MB 2.58 1.17 1.56
TDK veloCD 40/12/48 1.58 1.29 1.58
% faster than Zip 750 63.2% 9.30% 1.26%
slower
The veloCD with 12x rewritable media loses Test 1 quite handily to the Zip 750MB. However, tests 2 and 3 have
TDK's drive pulling ahead with small leads. As a reference point, the difference in recording time between both
drives for Test 1 was just over 2.5 minutes.
Read tests
Our results are in MB/s, with higher numbers being better.
CD-RW VS Zip 750MB Read Test: results in MB/s, higher is better Test 1 Test 2 Test 3
Zip 750MB 4.74 1.84 4.51
TDK veloCD 40/12/48 3.46 2.18 3.31
% faster than veloCD 40/12/48 36.9% 18.5% 36.2%
slower
The Zip 750MB gained two strong wins. Test 2 is a folder containing over 5,400 files, and our results highlight
the increased overhead generated when trying to transfer many small files.
Regardless of Windows' removable media optimization settings, the veloCD using CD-R (write once)
media was faster than the Zip 750MB in every one of our read/write tests.
Depending on the optimization settings, the veloCD was able to write data 20-665 percent (yes, over 6x)
faster than the Zip 750MB. Read speeds were a bit less dramatic with the veloCD managing a 5-48
percent advantage.
Our use of CD rewritable media evened the playing field when comparing the Zip 750MB to the veloCD, but
blank media costs are difficult to ignore. While it is easy to find bulk CD-R/RW media for under $1 a disc,
estimated prices of an eight-pack of 750MB Zip disks put the cost per disc at about $12.50.
For users who want a hard-drive-like environment to store their files, with the ability to quickly and easily
password-protect a disk, the Zip 750MB provides the means. Zip cartridges do a better job of protecting the
magnetic media within, but its estimated life of five years with regular usage is about a tenth of that of a CD.
Summary: The Zip 750MB offers performance comparable to CD recorders, but it isn't as easy to share.
Pros: Rugged media; small drive footprint.
Cons: Not as fast as CD-R; expensive media; cannot write to 100MB Zip disks