Chap72&73

DIGITAL MEDIA FUNDAMENTALS

Explain the various methods of storing and retrieving images. Compare the advantages and

limitations of these methods.

Explain the various methods of storing and retrieving images. Compare the advantages

and limitations of these methods.

In This Chapter, you’ll learn on: the various storage media the advantages and limitations of the various

storage media Planning for adequate back-up of data files and

disaster recovery. Checking for file integrity and errors.



Sound Formats for multimediaAbout Storage Media

Without digital storage media like hard disks, cd’s, dvd’s, servers and so on, your computer will be just like a standalone video player, only processing digital signals and nothing more.

These storage devices are non-volatile, meaning that they do not require constant power to store information. Thus they are most suitable for long term storage of information. On the opposite side are components like computer RAM where memory storage is dynamic but used only temporarily to aid processes.



Sound Formats for multimedia About Storage Media

Most digital storage data devices are accessed sequentially, thus there will be seek time and latency to access any data on the devices.

Of course there are other different kinds of storage devices, not just those that store your photos, music and other digital data.



What is a Tape Media? A tape drive is a peripheral hardware

device that reads and writes data into non-volatile magnetic tapes. A magnetic tape that resembles a conventional audio cassette tape, contains a magnetized coating on a thin plastic strip which data is written on.

Unlike dynamic and random storage mediums such as hard disks and flash drives, a tape drive operates using indexing and sequential-access. You have to run a tape from beginning to the end to perform a read or write operation. This means that data is written to the tape in one continuous stream.



What is a Tape Media? To read a particular piece of information,

the tape must wind past all preceding data to access it. Quite simply, a tape drive is like a cassette recorder that stores large volumes of digital data. Due to its cost efficiency and long shell life, tape drive makes a popular device for backup and archival purposes.



How Does it Work? A tape drive uses a controlled motor to wind the

tape from one reel to another with its magnetic strip passing a read/write head.

To cope with the difference between the rate which data is written into the tape and the data streaming to or from the computer or host, the tape drives incorporates a tape drive controller, which performs buffer procedures and logical operations such as ECC (Error Correction Code) during the data storage process.



How Does it Work? During a backup process, the computer memory buffer is

loaded with the data information from the host computer and sent to the controller's buffer. The controller then commands the recording mechanism to write the data into tape. When it completes, more data is loaded into the controller buffer from the computer and the cycle repeats itself until all data has been completely stored.

Storage capacity of tape drives range from a few hundred megabytes to several Terabytes compressed. They support compression capability and transfer rate of over 500MB/s. Tape drives are interoperable and usually connected to the computer via SCSI, IDE, USB and Firewire.



Tape Drive comes in several formats or standards: AIT (Advanced Intelligent Tape) AIT is 8mm across and uses helical scanning technique

and the MIC (Memory In Cassette) technology to provide increased access. It also supports high data transfer rate up to 78 MB/sec and maximum storage capacity of 500GB compressed using ALDC (adaptive lossless data compression) technologies.



Tape Drive comes in several formats or standards: DAT (Digital Audio Tape) DAT is 4mm across and offers over 40GB of storage at a

data transfer speed of about 5 Mb per second and is optimized for high volume backups.

DLT (Digital Linear Tape) DLT uses a technique to write data onto the tape in 128

or 208 linear tracks. DLT cartridges can contain around 70GB of data with compression. SuperDLT, a new DLT variant supports tape capacity up to 300GB(SDLT 600) and transfer data at speeds up to 36MB/sec.



Tape Drive comes in several formats or standards: LTO (Linear Tape-Open) LTO uses an open-format technology that provides

compatibility to various storage media products. It supports a capacity up to 6.4 Terabytes and transfer rate of 540MB/s.

Packet Tape Packet Tape - available from VXA (tape manufacturer)

has a capacity of 33GB native and 66GB compressed. It is an 8mm format and one that is commonly used by home-based business owners.



Hard DisksWhat is a Hard Disk? Once known as the Winchester drive, the hard disk or

hard drive is an essential hardware that every computer desktop and server contain. And its functionality, is to store vast amount of digital data in a non-volatile form, so that data can be retained when the computer is powered off. Data is again accessed when the power is on.



How hard disks work Hard disks is a growing storage medium, used in desktop

computers, laptop computers, video recorders, game consoles, portable players and much more.

Based on the principles of magnetism much like cassette tapes and floppy disks, hard drives are not immune to failure. As such, it is important to take care of your hard disk, and use it carefully.



Types of Hard Disks There are a few different types of hard disk but, other

than its physical size, the different type of interfaces of the hard disk is the main difference.

Types of hard disk interfaces • Desktop Hard Disk Types: 3.5', IDE and Sata

Interfaces • Laptop Hard Disk Types:2.5', 1.8', IDE, Sata, SCSI • Server Hard Disk types:3.5' Sata, SCSI



Types of Hard Disks There are a few different types of hard disk but, other

than its physical size, the different type of interfaces of the hard disk is the main difference.

Types of hard disk interfaces • Desktop Hard Disk Types: 3.5', IDE and Sata

Interfaces • Laptop Hard Disk Types:2.5', 1.8', IDE, Sata, SCSI • Server Hard Disk types:3.5' Sata, SCSI



What are Zip Cartridges? Looking akin to their 1.44MB floppy disk predecessors,

IOMEGA zip disks are sized slighter bigger but armed with the capacity to store over 100 to 700 times more data.

The Zip data drive was released in the late 1994 by IOMEGA as a removable storage solution to be used in mainstream IBM PCs and Macintosh computers. At that time, as the choices of storage meida are few, Iomega Zip soon took over the storage market by storm. Due to its proprietary nature, a zip drive is used to access the disks.



Beneath the Technology There are two distinct features that distinguish a zip

disk from a floppy. A zip disk is manufactured with a high quality magnetic

coating which allows its set of read/write head to be significantly smaller compared to that of a floppy. It uses a read head positioning mechanism similar to that used in a hard disk that allows a zip disk to pack thousands of tracks per inch on the track surface hence by providing a higher real density.

Secondly, read and write protection is introduced logically via a password. Unlike a floppy which implements write protection on the hardware level, zip disks contain a software meta data which stores the protection status. Each time a user accesses the disk, the meta data will be processed and enforced by the operating system.



Beneath the Technology There are two distinct features that distinguish a zip

disk from a floppy. The latest 750MB series supports data transfer rate of

about 7.5 MB/s and a 28 milliseconds average seek time as compared to a standard floppy's 500 Kbit/s transfer rate and several-hundred millisecond average seek time. Zip disks are also available in commonly 100MB, 250MB and 750MB sizes.



What is an Optical Disc? An optical disc is a flat piece of circular polycarbonate

plastic containing a non-volatile recording medium that stores digital information.

Data is then accessed with a laser diode illuminating on its recording medium.

To date, many forms of optical disc have been developed. Each generally enjoys a span of popularity of use before newer discs with greater capacity and capability are introduced into the market.

Nearing obsolete media includes Laser disc and Video CD (VCD) while trendy media such a CD (compact disc), CD-R, CD-RW, DVD-R, DVD-RW continue to thrive in our world of digital data and storage.



CD-R A CD-R is coated with a photosensitive organic dye

between the polycarbonate substrate and the light reflective layer. Referred as a WORM (Write Once, Read Many) media, data can only be written once permanently.

Every CD-R contains a spiral groove or track to guide the movement of the laser beam, provide time measurement and support various controls during data reading and writing.

This track makes about 22,188 revolutions around the disc.



CD-R Coated on one side of the disc with a thin layer of dye

and subsequently with a layer of reflective metal or alloy, a layer of photo-polymerizable lacquer is applied at the top to protect the metal reflector from U-V irradiation.

CD-R is widely used around the world due to its low cost and availability. It can be accessed by any multimedia computers or operating system that supports CD-ROM capability.

Furthermore, it does not require any special software to read the media. Due to its nature, it is often used for archiving purposes.



How Does CD-R Work? A typical CD-R has a storage capacity of 74 minutes of

audio or 650 MB of data. Used with a CD-Burner or recorder, users can easily store

music and data files with the ease of popular CD recording software such as Roxio Easy CD Creator and Ahead Nero. Windows XP also has its own built-in tool which users can burn CD using the drag and drop method.



Recording Process The recording begins with the laser indenting small pits

(or tiny indentations) on the dye surface of the disc. The heat of the laser 'burns' each pit through a chemical reaction, causing it to become opaque.

This pit will then reflect less light than the areas that are not heated by the laser. This irreversible process starts from the innermost region of the disc to the outermost region.

When the laser reads the disc, it scans the refractive dye along the groove and reads the change of reflectivity which decodes into electrical signals which is subsequently encoded into binary bits to be processed by the computer.

So you could see that optical disc is unlike hard disk drives which store the data on platter as magnetic flux.



CD-R Writing Speed CD-R is manufactured in various write-speed. This value

measures how fast data can be written into the disc by a CD-Recorder.

This is also dependent on the capability of CD-Recorders. CD-Recorders support various speed which is usually indicated by 3 numbers each separated with a hyphen.

For example, 40X-24X-48X features that the writer can support up to a maximum of 40-times write speed, 24-times rewrite speed and 48-times read speed. 5 years ago, you could burn a full CD-R in 45 minutes when the first writable disc was introduced. Today, you can replicate a full CD within 5 minutes with high speed media.



CD-R Dye The most common organic dye used for manufacturing

CD-R are Cyanine, PhthaloCyanine and Metallized Azo. Of all three, Cyanine has the shortest lifespan of about

10 years due to its weak reflection contrast caused by chemical instability. Cyanine-based CD-Rs are also susceptible to direct sunlight and are the cause of common read errors in CD-ROMS.

Metallized Azo dye is typically blue while PhthaloCyanine dye comes in silver, gold or transparent in colour. Azo and PhthaloCyanine are chemically stable and have a longer shell life.



CD-RW An acronym for Compact Disc Re-Writable, CD-RW is a

rewritable version of a CD or CD-R. With all functionality alike, the CD-RW is designed to counter the restriction of a CD-R, allowing users to store, erase, and rewrite new data into the disc.

Manufacturers have claimed that CD-RW can be reused over a thousand times. The lifespan of a CD-RW is typically dependent on the quality of its recording medium and abuse tolerance. Other attributes include the handling of the disc and the recording techniques employed by the CD-Burner which writes data into the disc.



CD-RW Most CD-RW today supports up to a capacity of 700MB of data

or 80 minutes of music. UDF or Universal Disk Format is a file system that can be employed to a CD-RW (CD-R also supports this feature) to render the disc randomly readable and writable like a floppy diskette.

The storage capacity of the disc will however be restricted to approximately 500MB. This implementation helps users who work with ever-changing data.



How Does CD-RW Work? A CD-RW contains a phase-change recording medium, usually

made of silver, indium, antimony and tellurium and an aluminium reflecting layer.

Alike a CD-R, the laser in the CD-Burner heats the crystal recording layer and transform it into a non-crystalline amorphous phase. By controlling the intensity and temperature, crystalline and non-crystalline areas are formed on the disk.

Non-crystalline areas will have a poorly reflective contrast compared to the crystalline areas. Data is hence by marked by the 'pits' and 'lands' of the disk.



How Does CD-RW Work? When the computer needs to access disc, the laser then read

the disc reflectivity, as it scans along the spiral groove. This difference will be registered as digital data, as the light

pulses are decoded into electrical signals which are subsequently encoded into binary bits to be processed by the computer.

To erase data on the disc, the laser anneals the recording medium at a lower temperature and transforming it back into a crystalline state again.

Users can continue to reuse the disc until the recording medium denatures and becomes unusable.



What is DVD? Introduced to the market in year 1997, DVD (also known as

Digital Versatile Disc or Digital Video Disc) has become the latest generation of optical disc storage technology. Even though it's physical dimension is the same with compact discs (i.e. 8cm or 12cm in diameter), DVD takes its advantages of having much higher density with a single data format. Minimum DVD storage of data is 4.7GB; however its maximum storage capability can be up to 26 times as much as a standard CD-R. Compared with CD technology, DVD allows for better quality of graphics, resolution and surrounded sound. Nowadays, DVD's widespread has gain support from major numbers of electronic companies, computer hardware companies, and also music and audio studios all over the world.



DVD ARCHITECTURE DVD is a 0.6mm thick disc made of poly-carbonate plastic and

has a very much thinner reflective layer made of gold or aluminium. Two 0.6mm discs are joined together to form a 1.2mm thick DVD bonded-disc that allows data to be read from either one side (single-sided) or two sides (double-sided) by laser beam.

In DVD, lens with higher Numerical Aperture (i.e. NA) is achieved to refine the laser assembly; hence allow usage of lesser smaller pits and narrower tracks. Modulation scheme of 8 to 17 (EFM PLUS) is used to provide DVD more efficient backward compatibility.



DVD ARCHITECTURE Another special and outstanding feature adopted by DVD is the

powerful technique of error correction to recover from even large scratches with nearly no loss of data. The RS-PC (Reed Solomon Product Code) is used in this technique which allows as 10 times more robust than which is currently used in CD system. Also, DVD is provided with several configurations of data reader ranging from 2D to 3D storage. Each configuration allows different additional storage capacity.



DIFFERENT FORMATS OF DVD DVD-ROM Provide high-capacity computer ROM storage. Data types

stored range from multimedia, computer games, interactive systems to databases. DVD includes variety of recordable variations including DVD-R, DVD-RAM, DVD+RW and DVD-RW D-ROM

DVD-Audio Provides far higher quality surround-sound music with

increased playing time.



DIFFERENT FORMATS OF DVD DVD-Video Provides high-quality multi-lingual movies on one disk with

random-access to episodes and surround-sound audio.

What is a Flash Drive? Equipped with a NAND-type flash memory and integrated with

a USB 1.1 or 2.0 interface, a flash drive is a removable, compact and non-volatile data storage device that acts like a portable hard disk. However unlike the size of the latter, a flash drive is usually no longer than a cigarette lighter and only weighs half an ounce.



Mechanics Encased in a robust plastic casing, the flash drive contains a

small printed circuit that connects to an embedded flash memory and a USB connector. This USB connector often protruded out of its casing to allow the user to plug the drive into the computer's USB port. For safety purposes, a plastic cap is usually designed to cover and protect the USB connector.

How Does it Work? When a flash drive is plugged into a computer's USB port, the

system's plug and play capability detects the new hardware and displays a new logical drive in the My Computer workspace. Users can then access the drive by double clicking on the drive icon and simply drag any files across for transmission instantly.



Developement The flash drive was designed for its portability and

interoperability to replace bulky diskettes and CD-RWs that were used to transfer files between two or more machines.

Back in 1980, floppy diskettes were popular removable storage media when file sizes were generally small. Today, a word document file containing graphics, charts and macro codes can easily amount to 10MB as compared to a few hundred kilobytes before 2001. CD-RWs soon replaced the 1.44MB diskettes to combat the file constraint. However, re-writable discs are proprietary media that require a CD-writer and software to store data.

When the flash drive was made available, it eliminated both problems and allows machines to read and write data without the need of any software or peripheral devices.



Developement The flash drive was designed for its portability and

interoperability to replace bulky diskettes and CD-RWs that were used to transfer files between two or more machines.

Back in 1980, floppy diskettes were popular removable storage media when file sizes were generally small. Today, a word document file containing graphics, charts and macro codes can easily amount to 10MB as compared to a few hundred kilobytes before 2001. CD-RWs soon replaced the 1.44MB diskettes to combat the file constraint. However, re-writable discs are proprietary media that require a CD-writer and software to store data.

When the flash drive was made available, it eliminated both problems and allows machines to read and write data without the need of any software or peripheral devices.



Using the Drive The flash drive does not require an external power supply.

Essentially, it runs off the small power supplied by the USB connection and is compatible with any computer that supports the Universal Serial Bus capability.

New USB Flash Drives now support transfer rates up to 480 Mbits/s and storage capacity up to several GB.

Due to heavy marketing and product branding, flash drives have been coined and associated with names such as USB drive, key drive, thumb drive, keychain drive etc.



What is RAID? To understand RAID, imagine multiple disk drives that are put

together and interlinked in an array to obtain greater performance, capacity and reliability.

RAID is an acronym for Redundant Array of Independent Disks - the technique that was developed by researchers at the University of California at Berkeley during 1987 to overcome the limitation and deficiency imposed by a single hard disk.



Using RAID RAID became popular when the needs of new applications and

devices are beyond the capability of a typical single hard disk. Special hard disks are expensive and RAID thus became an affordable alternative to large storage system that requires speedy data transfer rates and security.

RAID is now commonly used on computer server to reliably store large chunks of data. With the availability of RAID options now integrated into motherboard chipsets and operating systems, desktop and high-end users are starting to employ this technology to operate the storage-intensive tasks, such as non-linear video/audio editing and critical real-time operations.



Advantages of RAID Disk The key design of RAID is to provide data integrity, fault

tolerance, throughput and expandability. RAID can be set to various configurations to increase I/O disk

performances by merging the efficiency of two or more hard drives into one logical volume or exploiting the redundancy of a second drive for data replication and integrity.

Data back up and disaster recovery Disaster recovery is the process, policies and procedures

related to preparing for recovery or continuation of technology infrastructure critical to an organization after a natural or human-induced disaster. Disaster recovery is a subset of business continuity. While business continuity involves planning for keeping all aspects of a business functioning in the midst of disruptive events, disaster recovery focuses on the IT or technology systems that support business functions.



Strategies Prior to selecting a disaster recovery strategy, a disaster recovery

planner should refer to their organization's business continuity plan which should indicate the key metrics of recovery point objective (RPO) and recovery time objective (RTO) for various business processes (such as the process to run payroll, generate an order, etc.). The metrics specified for the business processes must then be mapped to the underlying IT systems and infrastructure that support those processes.[4]

Once the RTO and RPO metrics have been mapped to IT infrastructure, the DR planner can determine the most suitable recovery strategy for each system. An important note here however is that the business ultimately sets the IT budget and therefore the RTO and RPO metrics need to fit with the available budget. While most business unit heads would like zero data loss and zero time loss, the cost associated with that level of protection may make the desired high availability solutions impractical.



The following is a list of the most common strategies for data protection.

Backups made to tape and sent off-site at regular intervals Backups made to disk on-site and automatically copied to

off-site disk, or made directly to off-site disk Replication of data to an off-site location, which

overcomes the need to restore the data (only the systems then need to be restored or synchronized). This generally makes use of storage area network (SAN) technology

High availability systems which keep both the data and system replicated off-site, enabling continuous access to systems and data

In many cases, an organization may elect to use an outsourced disaster recovery provider to provide a stand-by site and systems rather than using their own remote facilities.



In addition to preparing for the need to recover systems, organizations must also implement precautionary measures with an objective of preventing a disaster in the first place. These may include some of the following:

Local mirrors of systems and/or data and use of disk protection technology such as RAID

Surge protectors — to minimize the effect of power surges on delicate electronic equipment

Uninterruptible power supply (UPS) and/or backup generator to keep systems going in the event of a power failure

Fire preventions — alarms, fire extinguishers Anti-virus software and other security measures



File integrity monitoring File integrity monitoring is an Internal control or Process that

performs the act of assuring Integrity of Operating system and Application software files using a verification method between the current file state and the known, good baseline. This comparison method often involves calculating a known Checksum of the operating system or file's original baseline and comparing with the calculated checksum of the current state of the operating system or application file.

Generally, the act of performing File integrity monitoring is automated using internal controls such as an application or process. Such monitoring can be performed randomly, at a defined polling interval, or in real-time.

Checking integrity of a file is the best way of telling whether it is corrupt or not? SFV and MD5 are two common formats used to check the integrity of files.



Simple file verification (SFV) It is a file format for storing CRC32 checksums of files in order to

verify the integrity of files. SFV can be used to detect random corruptions in a file, but cannot be used for checking authenticity in any meaningful way.

Message-Digest algorithm 5 (MD5) It is a widely used cryptographic hash function with a 128-bit

hash value. As an Internet standard (RFC 1321), MD5 has been employed in a wide variety of security applications, and is also commonly used to check the integrity of files.



FlashSFV is a free portable tool for Windows that allows you to create SFV files and also checks the integrity of files. With it, you can determine which files are corrupt and which are fine. Note that any file can be corrupt due to a variety of reasons, including error in transmissions, write errors, bad flash memory, and so on.



To create an SFV file using this tool, select New and then select the files and the output destination to save the SFV file. To check a SFV file, click Open, select the SFV file and then click Check. There is also an option to Verify the integrity of files.

You can associate the SFV and MD5 formats to FlashSFV, add options in Windows Explorer contextmenu, and change few other settings by going to Options.

It is quite an easy-to-use tool when compared with other Integrity checkers. It works on all versions of Windows.