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Home , Compact disc, Digital Data Storage, Disk storage, DVD, NT (cassette), Photo CD

1. Explain CD () TECHNOLOGY

A compact disc, also known as a CD, is a with a metalized surface that is used for digital .. This format was later adapted for storage of data (CD-ROM), write-once audio and data storage (CD-R), rewritable media (CD-RW), 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 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 or DVD and Blu-ray for video.

A CD typically holds 74 to 79 minutes of audio. The CD debuted in 1982 under Electronics and Corporation. The basic compact disc is simple in appearance, but consists of multiple layers. The base layer is polycarbonate plastic which holds the .

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 pits rest along tightly coiled spiral tracks followed by a laser. The reflected laser beam hits a that converts the binary data into an electrical that is heard like the original audio.

Cross section view of a compact disk

Understanding the CD: The Spiral

A CD has a single spiral 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 a CD that stores data of graphics, text and audio. They are popular for 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 written by a consumer using disc recording hardware, thus following the format 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 , images, music, document imaging and data archiving. In the beginning, there 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 provides flexible 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 standard under the moniker CD-RW in 1997. CD-RWs are designed for computer storage and 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 and customization. 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.

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

The DVD was introduced to a test-marketed U.S. in 1997 and developed by , Philips, Sony and Time Warner. are a consumer-friendly format primarily used for home 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 , video cartridges and 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 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 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.

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 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.

DVD pit layout

The microscopic dimensions of the bumps make the spiral track on a DVD extremely long. If you could lift the data track off a single layer of a DVD, and stretch it out into a straight line, it would be almost 7.5 miles long! That means that a double-sided, double-layer DVD would have 30 miles (48 km) of data.

Different types of DVDs:

1. DVD-ROM: DVD-ROM - or Digital Versatile Disc, Read-Only Memory - refers to the original DVD format of a high capacity optical storage disc that can only be read and not written. Data is already pre-recorded on the disc by the manufacturer when it reaches the consumer. Movie rentals, retail movies and large software applications are all examples of DVD-ROMs in the global market.

2. DVD-R: DVD-R (Digital Versatile Disc-Recordable) is one of the recordable formats available on the DVD market created by Pioneer in 1997. DVD-R is a write-once format where the initial record is burned permanently into the disc and cannot be erased. A DVD-R's approximate lifespan is 100 years.

3. DVD-R DL: DVD-R DL (Digital Versatile Disc-Recordable Dual Layer) is an optical disc of the DVD family that contains two recordable dye layers. The dual layer recordable disc is an extension of the DVD-R format and is also known by the name DVD-R9. This disc can only be written once, and it holds up to 8.5 GB of storage. It stores close to double the data of a single layer disc, but not quite double in order to avoid cross-recording of layers. Pioneer developed this disc format for the DVD Forum - the industry's premier association. 4. DVD-RW: DVD-RW (Digital Versatile Disc-Rewritable) is an optical storage disc of the 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 directly compete 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, plus format) 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 the DVD+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 professional grade 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.

3. Benefits of DVD over CD.

 DVD has Higher Storage Capacity

DVDs can store more data than CDs for a few reasons:

 Higher-density data storage  Less overhead, more area  Multi-layer storage  Higher Density Data Storage Single-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 830 nanometres 400 nanometres (single-layer DVD)

Minimum Pit Length 830 nanometres 440 nanometres (double-layer DVD)

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 minimum pit 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 Area On 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 Double-sided/single-layer 8.75 GB 4.5 hours

Double-sided/double-layer 15.9 GB Over 8 hours

Why the capacity of a DVD doesn't double when you add a whole second layer to the disc?. This is because when a disc is made with two layers, the pits have to be a little longer, on both layers, than when a single layer is used. This helps to avoid interference between the layers, which would cause errors when the disc is played.

There are two essential physical differences between CD and DVD disc.

 First, the smallest DVD pits are only 0.44 micron in diameter; the equivalent CD pits are nearly twice as large, or 0.83 micron wide. And DVD data tracks are only 0.74 micron apart; whereas 1.6 microns separate CD data tracks. So although a DVD is the same size as a CD, its data spiral is upward of 11 kilometres long-more than twice the length of a CD's data spiral. To read the smaller pits, a DVD player's readout beam must achieve a finer focus than a CD player's does. In order to do this, it uses a read semiconductor laser that has a wave length of 635 to 650 nanometre. In contrast, CD players use infrared laser with a longer wavelength of 780 nanometre. Also, DVD players employ a more powerful focusing lens-one having a higher numerical aperture than the lens in a CD player. The differences, together with the additional efficiencies of the DVD format described below, account for the huge 4.7-gigayte capacity of each DVD information layer.  A DVD’s capacity can be doubled to 9.4 -and nearly doubled again to about 17 gigabytes- by two more innovations. Although DVDs and CDs have the same overall thickness-11.2 millimetre- DVDs possess two substrates that can carry information' whereas CDs have one. A DVD 's substrates are bonded together so that their pitted surfaces face each other in the centre of the of the disc.This setup shields the surfaces from the damaging effects of dust particles and scratches. 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.)

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 , 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 GB of data -- that's more than two hours of high-definition video or about 13 hours of standard video.  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 Disc

Blu-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 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 laser to read and write data, Blu-ray uses a (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 (µm) (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 polycarbonate layers, 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.

 How Blu-ray reads Data

The 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.

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 .

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

4. Differences between NTFS and FAT FILE systems.

Over those years, operating systems have evolved through two different file systems: FAT and NTFS. Operating systems have come a long way since was measured in . Over those years, Microsoft operating systems have evolved through two different file systems: FAT and NTFS. Here's how they differ. FAT ()

The original 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 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 (MB) of storage space.

* FAT 16: When personal computers began the transition from 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 it’s most likely to use.

* FAT 32: After the dramatic increases in hard drive size during the , 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 they’re stable and can work with simple computer systems, such as ROM-based computers or handheld devices.

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 more control 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 don’t compress files or storage devices unless they’re 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 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 drive letter 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.

 Comparison between NTFS and FAT

NTFS FAT 16/32

 Default File system In Windows XP, 2k and NT  Fat 16 not compatible with XP, FAT is more

 Support For Drives over 40gb, Files over GB compatible with other operating Systems( Windows

 Allows extended file names, foreign characters 95, etc)

 Has a severely crippled maintenance system in  FAT 16 has 8.3 character limitation

chkdsk  Has better, more and interactive recovery utilities

 Chkdsk is notoriously slow (scandisk)

 Increased security with file encryption  Scandisk is very quick

 Smaller file clusters, 4kb  Just a space for the OS to read files

 Compression to reduce disk space  Faster on drives less than 10gb

 User permissions for files and folders  FAT 16 cluster size is 32kb

 File copies are “undone” if interrupted, cluster chains  Cluster chains containing data from interrupted

is cleaned copies are marked as damaged

 Small files are kept in Master File Table at the  Master File Table are separate from files

beginning of the drive

 Not compatible with different operating systems on

the same computer