CD and DVD Technologies and Their Differences

7/31/2019 CD and DVD Technologies and Their Differences

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1. Explain CD (COMPACT DISC) TECHNOLOGY

A compact disc, also known as a CD, is a plastic optical disc with a metalized surface that isused for digital data storage.. This format was later adapted for storage of data (CD-ROM),

write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Discs

(VCD), Super Video Compact Discs (SVCD), Photo CD, Picture CD, CD-i, and Enhanced

CD.

When a compact disc is played, the information is read by a laser and converted into sound

that represents an original audio source. The CD's storage capabilities have expanded

alongside its technology to read other data like CD-ROM for computers or DVD and Blu-ray

for video.

A standard CD typically holds 74 to 79 minutes of audio. The CD debuted in 1982 under

Philips Electronics and Sony Corporation. The basic compact disc is simple in appearance,

but consists of multiple layers. The base layer is polycarbonate plastic which holds the digitaldata.

This layer is topped by an aluminium coating that serves to reflect the laser that reads the

disc's information. (In rare instances, silver or gold may be used in place of aluminium). A

clear layer of shiny acrylic protects the aluminium. The standard CD has a 12 cm diameter

and a 1.2 mm thickness. From its centre outward, it consists of a spindle, a clamping ring, a

stack ring, a mirror band, an information area and the rim.

The CD's data layer is comprised of billions of tiny indentations called pits that are invisible

to the human eye. These pits are encoded with binary data (0's and 1's) that maintain the

disc's speed and sound. They also serve to control the disc player's laser. The patterns of pitsrest along tightly coiled spiral tracks followed by a laser. The reflected laser beam hits a

photodiode that converts the binary data into an electrical signal that is heard like the original

audio.

Cross section view of a compact disk
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Understanding the CD: The Spiral

A CD has a single spiral track of data, circling from the inside of the disc to the outside. The

fact that the spiral track starts at the centre means that the CD can be smaller than 4.8 inches

(12 cm) if desired, and in fact there are now plastic baseball cards and business cards that you

can put in a CD player. CD business cards hold about 2 MB of data before the size and shape

of the card cuts off the spiral.

What the picture on the right does not even begin to impress upon you is how incredibly

small the data track is -- it is approximately 0.5 microns wide, with 1.6 microns separating

one track from the next. (A micron is a millionth of a meter.)

Upper view of a CD.

Different types of CDs:

1. CD-ROM:CD-ROM stands for Compact Disc Read-Only Memory. It functions as aCD that stores computer data of graphics, text and audio. They are popular for

software and other multimedia applications. CD-ROMs commonly store up to 700MB

of information. This data comes pre-stamped by the manufacturer so it cannot be

erased nor edited.

2. CD-R:CD-R, or compact disc-recordable is a type of compact disc that can be writtenby a consumer using disc recording hardware, thus following the format acronym

WORM (write once, read many). CD-R's were engineered by the inventors of the

compact disc, Philips and Sony, and first available in 1988. A CD-R stores digital

video, images, music, document imaging and data archiving. In the beginning, there
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was a price gap due to copyright issues that made music CD-Rs more expensive than

data CD-Rs.

3. CD-RW: CD-RW, or Compact Disc-ReWritable, is a CD format that providesflexible recording options. This format permits optical data to be written, re-written,

read and erased multiple times. At its conception, it was known as CD-E (CD-

Erasable) but was introduced as an extension of the Orange Book standard under the

moniker CD-RW in 1997. CD-RWs are designed for computer storage and backup

since they can be re-written, but their re-writable format results in a disc with a

smaller storage capacity than a write-once CD-R disc.

4. PRINTABLE CD: A printable CD takes media to a higher level of creativity andcustomization. These discs are designed with a printable surface area to display

artwork without interfering with the function of the CD. These discs are available in a

variety of formats to suit the needs of specified printers as well as suit an artistic

vision. CD-R is the most popular format of printable CDs available. The less

frequently used CD-RWs are also available on the market.


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2. Explain DVD (DIGITAL VERSATILE DISC) TECHNOLOGY

The term DVD is an acronym for Digital Versatile Disc or Digital Video Disc, and it refers to

a type of optical disc used for storing data and video content. The capacity of a DVD is at

least seven times greater than a compact disc and provides enough room for a full-length

feature film. A DVD will support standard as well as widescreen television title views in 4:3and 16:9 aspect ratios.

The DVD was introduced to a test-marketed U.S. in 1997 and developed by Toshiba, Philips,

Sony and Time Warner. DVDs are a consumer-friendly format primarily used for home

entertainment for all mediums, as well as for business needs, storage backup and computer

software. DVDs took a strong reign over the global audio and video market by replacing

videotapes, video cartridges and laserdiscs as the mainstream format within a decade of its

debut.

DVD technology is akin to the next generation of the compact disc, as it mirrors its

technology. Both discs share the same dimensions of 1.2mm thickness and 120mm diameter.

The DVD contains microscopic pits of binary data on its polycarbonate layer like the CD, as

well as substrate, adhesive, reflective and lacquered layers, but the DVD's construction has

some singular exceptions.

The DVD's pits of data are smaller and rest closer together than those of a compact disc. This

higher density of pits allows a shorter laser wavelength that in turn allows more data to be

stored per track. The result is more efficiency in error correction and channel bit jitters. In

addition the disc has a thinner outer layer to let the reading laser pass through the extra layers

with more ease.

There are four basic constructions of the DVD depending on one's optical storage

requirements: single-sided single layer, single-sided double layer, double-sided single layer

and double-sided double layer. A shift by the drive's laser is all that is needed to read the next

layer which therefore allows more storage per disc while eliminating the need to switch discs

between projects or media entertainment.

Storage capacity does not completely double with the addition of another layer. Rather, the

pits on the second layer must be constructed longer and less dense in order to combat

obstruction and errors between layers. Dual layer and single layer DVD drives have

comparable costs; however the recordable media itself still has a market separation.


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DVDs are of the same diameter and thickness as CDs, and they are made using some of the

same materials and manufacturing methods. Like a CD, the data on a DVD is encoded in the

form of small pits and bumps in the track of the disc.

A DVD is composed of several layers of plastic, totalling about 1.2 millimetres thick. Each

layer is created by injection moulding polycarbonate plastic. This process forms a disc that

has microscopic bumps arranged as a single, continuous and extremely long spiral track of

data. More on the bumps later.

Once the clear pieces of polycarbonate are formed, a thin reflective layer is sputtered onto the

disc, covering the bumps. Aluminium is used behind the inner layers, but a semi-reflective

gold layer is used for the outer layers, allowing the laser to focus through the outer and onto

the inner layers. After all of the layers are made, each one is coated with lacquer, squeezed

together and cured under infrared light. For single-sided discs, the label is silk-screened onto

the no readable side. Double-sided discs are printed only on the no readable area near the

hole in the middle. Cross sections of the various types of completed DVDs (not to scale) look

like this:

Data tracks on a DVD

Each writable layer of a DVD has a spiral track of data. On single-layer DVDs, the track

always circles from the inside of the disc to the outside. That the spiral track starts at the

centre means that a single-layer DVD can be smaller than 12 centimetres if desired.

What the image to the right cannot impress upon you is how incredibly tiny the data track is -- just 740 nanometres separate one track from the next (a nanometre is a billionth of a meter).

And the elongated bumps that make up the track are each 320 nanometres wide, a minimum

of 400 nanometres long and 120 nanometres high. The following figure illustrates looking

through the polycarbonate layer at the bumps.

We will often read about "pits" on a DVD instead of bumps. They appear as pits on the

aluminium side, but on the side that the laser reads from, they are bumps.
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4. DVD-RW:DVD-RW (Digital Versatile Disc-Rewritable) is an optical storage disc ofthe DVD format that shares the same sizes as a DVD-R, however a DVD-RW can be

written, re-written and erased safely up to 1,000 times. They are likely to remain

readable by the user for up to 30 years; however manufacturers and changing

technology can affect this lifespan.

5. DVD+R:DVD+R is an optical write-once disc format specification made to directlycompete with DVD-R. It is supported and maintained by these manufacturers of the

DVD+RW Alliance but not limited to this scope and also subject to change: Philips,

Hewlett-Packard, Mitsubishi, Sony, Ricoh and Yamaha. DVD+R was introduced in

2002 - after its rewritable cousin (DVD+RW), which typically bucks the trend in

technical chronology.

6. DVD+R DL: DVD+R DL (Digital Versatile Disc, Recordable Dual Layer, plusformat) is an optical storage format that's an extension of the DVD+R format and

engineered by the DVD+RW Alliance in competition for market dominance with

its DVD-R DL rival. The recordable dual layer disc, also known as the DVD+R9 was

introduced in 2003 by Philips and MKM.

7. DVD+RW: DVD+RW is an optical storage rewritable disc format created by theDVD+RW Alliance as a market competitor of the DVD-RW (dash) format. It holds a

high capacity of audio and video that can be read, written, erased and re-written

dependably up to 1,000 times per disc. The format can accommodate one or two layer

discs. DVD+RW was publicly introduced in 2001 at a 4.7B storage capacity.

8. PRINTABLE DVD: Function and art merge as printable DVDs provide professionalgrade media with a personal touch. Grade-A printable DVDs come in single and dual

layer formats. No matter the storage capacity, each DVD format possesses a printable

surface area for custom artwork. Printable DVDs are also versatile to a variety of

printing options. Printable discs are like a blank canvas to a user's project-they

provide room for creativity without compromising the integrity of the data stored on

the DVD.
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3. Benefits of DVD over CD.

DVD has Higher Storage CapacityDVDs can store more data than CDs for a few reasons:

Higher-density data storage Less overhead, more area Multi-layer storage

Higher Density Data StorageSingle-sided, single-layer DVDs can store about seven times more data than CDs. A

large part of this increase comes from the pits and tracks being smaller on DVDs.

Specification CD DVD

Track Pitch 1600 nanometres 740 nanometres

Minimum Pit Length

(single-layer DVD)830 nanometres 400 nanometres

Minimum Pit Length

(double-layer DVD)830 nanometres 440 nanometres

Let's try to get an idea of how much more data can be stored due to the physically tighter

spacing of pits on a DVD. The track pitch on a DVD is 2.16 times smaller, and the minimumpit length for a single-layer DVD is 2.08 times smaller than on a CD. By multiplying these

two numbers, we find that there is room for about 4.5 times as many pits on a DVD.

Less Overhead, More AreaOn a CD, there is a lot of extra information encoded on the disc to allow for error

correction -- this information is really just a repetition of information that is already

on the disc. The error correction scheme that a CD uses is quite old and inefficient

compared to the method used on DVDs. The DVD format doesn't waste as much

space on error correction, enabling it to store much more real information. Another

way that DVDs achieve higher capacity is by encoding data onto a slightly larger area

of the disc than is done on a CD. Multi-Layer Storage

To increase the storage capacity even more, a DVD can have up to four layers, two on

each side. The laser that reads the disc can actually focus on the second layer through

the first layer. Here is a list of the capacities of different forms of DVDs:

Format Capacity Approx. Movie Time

Single-sided/single-layer 4.38 GB 2 hours

Single-sided/double-layer 7.95 GB 4 hours


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In the simplest design, the second DVD side is accessed by physically removing the disc

from the player removing the disc from the player, turning it over and reinserting it. Another

variation-the multilayer design enables both information surfaces to be payer from the side of

the disc.

In a multilayer disc, the upper substrate is coated with a partially reflective, partially

trasmissive layer. The reflectivity of the upper layer is sufficient to enable the laser to read

the pits in the upper substrate; its transmissivity also permits the beam to focus on the lower

substrate and read the pits on the in that layer. When the laser focuses on pits in the upper

information layer are out of focus and so do not interfere.(To accommodate the small but

unavoidable loss of paperback quality in this approach, a slight capacity reduction to 8.5

gigabytes unnecessary-which explains why a double-sided, double-layer DVD would hold

about 17 gigabytes.)


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4. BLU-RAY DISCS

In 1997, a new technology emerged that brought digital sound and video into homes all over

the world. It was called DVD, and it revolutionized the movie industry.

The industry is set for yet another revolution with the introduction of Blu-ray Discs (BD) in

2006. With their high storage capacity, Blu-ray discs can hold and play back large quantities

of high-definition video and audio, as well as photos, data and other digital content.

A current, single-sided, standard DVD can hold 4.7 GB (gigabytes) of information. That's

about the size of an average two-hour, standard-definition movie with a few extra features.

But a high-definition movie, which has a much clearer image (see How Digital Television

Works), takes up about five times more bandwidth and therefore requires a disc with about

five times more storage. As TV sets and movie studios make the move to high definition,

consumers are going to need playback systems with a lot more storage capacity.

Blu-ray is the next-generation digital video disc. It can record, store and play back high-

definition video and digital audio, as well as computer data. The advantage to Blu-ray is the

sheer amount of information it can hold:

A single-layer Blu-ray disc, which is roughly the same size as a DVD, can hold up to 27 GBof data -- that's more than two hours of high-definition video or about 13 hours of standard

video.
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A double-layer Blu-ray disc can store up to 50 GB, enough to hold about 4.5 hours of high-definition video or more than 20 hours of standard video. And there are even plans in the

works to develop a disc with twice that amount of storage

.

Building a Blu-ray DiscBlu-ray discs not only have more storage capacity than traditional DVDs, but they also offer

a new level of interactivity. Users will be able to connect to the Internet and instantly

download subtitles and other interactive movie features. With Blu-ray, you can:

record high-definition television (HDTV) without any quality loss instantly skip to any spot on the disc record one program while watching another on the disc create playlists edit or reorder programs recorded on the disc automatically search for an empty space on the disc to avoid recording over a program access the Web to download subtitles and other extra features

Discs store digitally encoded video and audio information in pits -- spiral grooves that run

from the center of the disc to its edges. A laser reads the other side of these pits -- the bumps -

- to play the movie or program that is stored on the DVD. The more data that is contained on

a disc, the smaller and more closely packed the pits must be. The smaller the pits (and

therefore the bumps), the more precise the reading laser must be.

Unlike current DVDs, which use a red laser to read and write data, Blu-ray uses a bluelaser (which is where the format gets its name). A blue laser has a shorter wavelength (405

nanometers) than a red laser (650 nanometers). The smaller beam focuses more precisely,

enabling it to read information recorded in pits that are only 0.15 microns (m) (1 micron =

10-6

meters) long -- this is more than twice as small as the pits on a DVD. Plus, Blu-ray has

reduced the track pitch from 0.74 microns to 0.32 microns. The smaller pits, smaller beam

and shorter track pitch together enable a single-layer Blu-ray disc to hold more than 25 GB of

information -- about five times the amount of information that can be stored on a DVD.

Each Blu-ray disc is about the same thickness (1.2 millimeters) as a DVD. But the two types

of discs store data differently. In a DVD, the data is sandwiched between two polycarbonatelayers, each 0.6-mm thick. Having a polycarbonate layer on top of the data can cause a

problem called birefringence, in which the substrate layer refracts the laser light into two

separate beams. If the beam is split too widely, the disc cannot be read. Also, if the DVD

surface is not exactly flat, and is therefore not exactly perpendicular to the beam, it can lead

to a problem known as disc tilt, in which the laser beam is distorted. All of these issues lead

to a very involved manufacturing process.
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How Blu-ray reads DataThe Blu-ray disc overcomes DVD-reading issues by placing the data on top of a 1.1-mm-

thick polycarbonate layer. Having the data on top prevents birefringence and therefore

prevents readability problems. And, with the recording layer sitting closer to the objective

lens of the reading mechanism, the problem of disc tilt is virtually eliminated. Because the

data is closer to the surface, a hard coating is placed on the outside of the disc to protect it

from scratches and fingerprints.

The design of the Blu-ray discs saves on manufacturing costs. Traditional DVDs are built by

injection molding the two 0.6-mm discs between which the recording layer is sandwiched.

The process must be done very carefully to prevent birefringence.

1. The two discs are molded.2. The recording layer is added to one of the discs.3. The two discs are glued together.

Blu-ray discs only do the injection-molding process on a single 1.1-mm disc, which reduces

cost. That savings balances out the cost of adding the protective layer, so the end price is no

more than the price of a regular DVD.


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A BD-ROM disc researcher holds a disc up to the light.

Blu-ray also has a higher data transfer rate -- 36 Mbps (megabits per second) -- than

today's DVDs, which transfer at 10 Mbps. A Blu-ray disc can record 25 GB of material in

just over an hour and a half.

ON GUARD

Blu-ray discs are better armed than current DVDs. They come equipped with a secure

encryption system -- a unique ID that protects against video piracy and copyright

infringement.

FORMATS

Unlike DVDs and CDs, which started with read-only formats and only later added recordable

and re-writable formats, Blu-ray is initially designed in several different formats:

BD-ROM (read-only) - for pre-recorded content BD-R (recordable) - for PC data storage BD-RW (rewritable) - for PC data storage BD-RE (rewritable) - for HDTV recording
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4. Differences between NTFS and FAT FILE systems.

Over those years, Microsoft operating systems have evolved through two different file

systems: FAT and NTFS.

Operating systems have come a long way since computer memory was measured in kilobytes.

Over those years, Microsoft operating systems have evolved through two different file

systems: FAT and NTFS. Here's how they differ.

FAT (FILE ALLOCATION TABLE)

The original file system developed by Microsoft to organize data on a storage medium is the

File Allocation Table (FAT). Because hard drives weren't available for personal computers in

the early days of PCs, the FAT system was developed for use with floppy disks. The

operating system uses the FAT system to locate files within the computer by pointing to the

starting cluster of the file. In addition to providing a way for the operating system to locate

files, the FAT contains filenames, time and date stamps, directory names, and file attributes.

For all intents and purposes, the FAT system is no longer used on new computer installations,

but is still recognized by operating systems. The distinct versions of FAT are described in this

list:

* FAT 12: Used only on floppy disks and released by Microsoft on its first operating system,

Microsoft Disk Operating System (MS-DOS) Version 1.0, the FAT 12 system is designed to

handle a whopping 16 megabytes (MB) of storage space.

* FAT 16: When personal computers began the transition from floppy disk storage to fixed

hard drive storage, the need for a file system that could handle media larger than 16MB

became critical. The FAT 16 file system could handle, in theory, as much as 2GB of storage

space. FAT 16 was the standard Microsoft file system from DOS version 3.0 until Microsoft

released Windows 95 version 2. When you run across an older computer, this file system is

the one its most likely to use.

* FAT 32: After the dramatic increases in hard drive size during the 1990s, the need arose for

a file system that could handle storage devices larger than 2GB. FAT 32 addressed this need:

It could handle as much as 2 terabytes (TB) under normal circumstances. Since the release of

Windows 95 version 2, the FAT 32 file system was an option for all subsequent Microsoft

operating systems as a way to provide backward compatibility with previous versions.

Even though FAT systems are somewhat ancient by computer standards, many older

operating systems are still in use now simply because theyre stable and can work with

simple computer systems, such as ROM-based computers or handheld devices.


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NTFS (NEW TECHNOLOGY FILE SYSTEM)

Microsoft had a lock on the residential computer market but needed an operating system with

more stability and security than Windows for Workgroups or DOS could offer for the

commercial and business markets. The design goals for the Windows NT operating system

were to be as secure as Unix, support long filenames, have network capability natively, and

not waste storage space the way FAT systems did. In 1993, Microsoft released Windows NT

3.1 with NTFS version 1.0, and it has been upgrading the NTFS capabilities with each new

release.

NTFS is a sophisticated file system in comparison to FAT in a number of respects. The NTFS

system has these features:

* Enhanced file attributes: In addition to the read-only, archive, system, and hidden file

attributes, NTFS includes file attributes such as indexed, compressed, and encrypted. NTFS

also has increased control over the permissions of files and folders to provide much morecontrol over how users access files.

* File compression: NTFS allows for transparent file compression of files. Because

compression tends to slow things down on a computer system and no real security advantage

results from compressing files, most users dont compress files or storage devices unless

theyre running out of room.

* Encryption: The Encrypting File System (EFS) provides a relatively good level of security

for protecting files and folders. The encryption system works transparently to the user who

initially encrypted the file or folder by associating the encryption keys with the user account

information and encrypting or decrypting at the system level.

* Journaling: With the release of NTFS, Microsoft introduced change logs to its operating

system. The journaling system on NTFS logs any changes made to the metadata associated

with files on the system.

* Shadow copy: This NTFS feature takes snapshots of files or folders at a specified point and

saves them for use by either the user or specific applications. Depending on the version of

Windows, the shadow copy feature has more or less capability between Windows versions.

* Mount points: One way to add logical volumes to NTFS without adding another driveletter is to use mount points. For example, you can add an entire new hard drive volume to

the existing logical volume C:, thus increasing the logical size of drive C without incurring

the hassle and labor involved in adding a new drive letter with all its associated path issues.


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Comparison between NTFS and FATNTFS FAT 16/32

Default File system In Windows XP, 2k and NT Support For Drives over 40gb, Files over GB Allows extended file names, foreign characters Has a severely crippled maintenance system in

chkdsk

Chkdsk is notoriously slow

Increased security with file encryption Smaller file clusters, 4kb Compression to reduce disk space User permissions for files and folders File copies are undone if interrupted, cluster chains

is cleaned

Small files are kept in Master File Table at thebeginning of the drive

Not compatible with different operating systems onthe same computer

Fat 16 not compatible with XP, FAT is morecompatible with other operating Systems( Windows

95, etc)

FAT 16 has 8.3 character limitation Has better, more and interactive recovery utilities

(scandisk)

Scandisk is very quick Just a space for the OS to read files Faster on drives less than 10gb FAT 16 cluster size is 32kb Cluster chains containing data from interrupted

copies are marked as damaged

Master File Table are separate from files

Documents

CD and DVD Technologies and Their Differences