Manual on Digital Storage

8/2/2019 Manual on Digital Storage

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Manual on digital storage

Digitizing or digitization is the representation of an object, image, sound, document or a

signal (usually an analog signal) by a discrete set of its points or samples. The result is calleddigital representation or, more specifically, a digital image, for the object, and digital form, for the

signal. Strictly speaking, digitizing means simply capturing an analog signal in digital form.

McQuail identifies the process of digitization having immense significance to the computing ideals

as it "allows information of all kinds in all formats to be carried with the same efficiency and also

intermingled".

Process

The term digitization is often used when diverse forms of information, such as text, sound, image

or voice, are converted into a single binary code. Digital information exists as one of two digits,

either 0 or 1. These are known as bits (a contraction of binary digits) and the sequences of 0s and

1s that constitute information are called bytes.Analog signals are continuously variable, both in the

number of possible values of the signal at a given time, as well as in the number of points in the

signal in a given period of time. However, digital signals are discrete in both of those respects

generally a finite sequence of integers therefore a digitization can only ever be an approximation

of the signal it represents. Digitization occurs in two parts:

Discretization

The reading of an analog signal A, and, at regular time intervals (frequency), sampling the value of

the signal at the point. Each such reading is called a sample and may be considered to have infinite

precision at this stage;

Quantization

Samples are rounded to a fixed set of numbers (such as integers), a process known as quantization.

In general, these can occur at the same time, though they are conceptually distinct.

A series of digital integers can be transformed into an analog output that approximates the original

analog signal. Such a transformation is called a DA conversion. The sampling rate and the number

of bits used to represent the integers combine to determine how close such an approximation to the

analog signal a digitization will be.


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Analog signals to digital

Analog signals are continuous electrical signals. Digital signals are non-continuous. Nearly all

recorded music has been digitized. About 12 percent of the 500,000+ movies listed on the Internet

Movie Database are digitized on DVD.

Implications of Digitization

This shift to digitization in the contemporary media world has created implications for traditional

mass media products, however these "limitations are still very unclear" (McQuail, 2000:28). The

more technology advances, the more converged the realm of mass media will become with less

need for traditional communication technologies. For example, the Internet has transformed many

communication norms, creating more efficiency for not only individuals, businesses also.

However, McQuail suggests traditional media have also benefited greatly from new media,

allowing more effective and efficient resources available

Collaborative digitization projects

There are many collaborative digitization projects throughout the United States. Two of the earliest

projects were the Collaborative Digitization Project in Colorado and NC ECHO - North Carolina

Exploring Cultural Heritage Online, based at the State Library of North Carolina. These projects

establish and publish best practices for digitization and work with regional partners to digitize

cultural heritage materials. Additional criteria for best practice have more recently been established

in the UK, Australia and the European Union.[8] Wisconsin Heritage Online is a collaborative

digitization project modeled after the Colorado Collaborative Digitization Project. Wisconsin uses

a wiki to build and distribute collaborative documentation. Georgia's collaborative digitization

program, the Digital Library of Georgia, presents a seamless virtual library on the state's history

and life, including more than a hundred digital collections from 60 institutions and 100 agencies of

government. The Digital Library of Georgia is a GALILEO initiative based at the University of

Georgia Libraries. In South-Asia Nanakshahi trust is digitizing manuscripts of Gurmukhi Script.

Digital preservation in its most basic form is a series of activities maintaining access to digital

materials over time.Digitization in this sense is a means of creating digital surrogates of analog

materials such as books, newspapers, microfilm and videotapes. Digitization can provide a means

of preserving the content of the materials by creating an accessible facsimile of the object in order

to put less strain on already fragile originals.


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information within most types of semiconductor (computer chips) microcircuits are volatile

memory, for it vanishes if power is removed.

With the exception of barcodes and OCR data, electronic data storage is easier to revise and may

be more cost effective than alternative methods due to smaller physical space requirements and the

ease of replacing (rewriting) data on the same medium. However, the durability of methods such as

printed data is still superior to that of most electronic storage media. The durability limitations may

be overcome with the ease of duplicating (backing-up) electronic data.

A tape drive is a data storage device that reads and writes data stored on a magnetic tape. It is

typically used for off-line, archival data storage. Tape media generally has a favorable unit cost

and long archival stability.

A tape drive provides sequential access storage, unlike a disk drive, which provides random access

storage. A disk drive can move its read/write head(s) to any random part of the disk in a very short

amount of time, but a tape drive must spend a considerable amount of time winding tape between

reels to read any one particular piece of data. As a result, tape drives have very slow average seek

times. Despite the slow seek time, tape drives can stream data to and from tape very quickly. For

example, modern LTO drives can reach continuous data transfer rates of up to 80 MB/s, which is

as fast as most 10,000 RPM hard disks.

Tape drives can range in capacity from a few megabytes to hundreds of gigabytes of uncompressed

data. In marketing materials, tape storage is usually referred to with the assumption of 2:1

compression ratio, so a tape drive might be known as 80/160, meaning that the true storage

capacity is 80 whilst the compressed storage capacity can be approximately 160 in many situations.

IBM and Sony have also used higher compression ratios in their marketing materials. The real-

world, observed compression ratio always depends on what type of data is being compressed. The

true storage capacity is also known as the native capacity or the raw capacity.

Tape drives can be connected to a computer with SCSI (most common), Fibre Channel, SATA,

USB, FireWire, FICON, or other[1] interfaces. Tape drives can be found inside autoloaders and

tape libraries which assist in loading, unloading and storing multiple tapes to further increase

archive capacity.

Some older tape drives were designed as inexpensive alternatives to disk drives. Examples include

DECtape, the ZX Microdrive and Rotronics Wafadrive. This is generally not feasible with modern


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tape drives that use advanced techniques like multilevel forward error correction, shingling, and

serpentine layout for writing data to tape.

An effect referred to as shoe-shining may occur during read/write operations if the data transfer

rate falls below the minimum threshold at which the tape drive heads were designed to transfer

data to or from a continuously running tape. When the transfer rate becomes too low and streaming

is no longer possible, the drive must decelerate and stop the tape, rewind it a short distance, restart

it, position back to the point at which streaming stopped and then resume the operation. The

resulting back-and-forth tape motion resembles that of shining shoes with a cloth.

In early tape drives, the situation of non-continuous data transfers was normal and unavoidable -

computers with weak processors and low memory were rarely able to provide a constant stream.

So, tape drives were typically designed for so called start-stop operation. Early drives used very

large spools, which necessarily had high inertia and did not start and stop moving easily. To

provide high start, stop, and seeking performance, several feet of loose tape was played out and

pulled by a suction fan down into two deep open channels on either side of the tape head and

capstans. The long thin loops of tape hanging in these vacuum columns had far less inertia than the

two reels and could be rapidly started, stopped and repositioned. The large reels would

occasionally move to take up written tape and play out more blank tape into the vacuum columns.

Later, most tape drive designs of the 1980s introduced the use of an internal data buffer to

somewhat reduce start-stop situations. These drives are colloquially referred to as streamers. The

tape was stopped only when the buffer contained no data to be written, or when it was full of data

during reading. As the tape speed increased, the start-stop operation was no longer possible, and

the drives started to suffer from shoe-shining (sequence of stop, rewind, start).

Most recently, drives no longer operate at single fixed linear speed, but have a few speed levels.

Internally, they implement algorithms that dynamically match the tape speed level to computer's

data rate. Example speed levels could be 50 percent, 75 percent and 100 percent of full speed. Still,

a computer that streams data constantly below the lowest speed level (e.g. at 49 percent) will

undoubtedly cause shoe-shining. When shoe-shining occurs, it significantly affects the attainable

data rate, as well as drive and tape life.

Magnetic tape is commonly housed in a casing such as plastic known as a cassette or a cartridge

for example, the 4-track cartridge and the compact cassette. The cassette contains magnetic tape to


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provide different audio content using the same player. The plastic outer shell permits ease of

handling of the fragile tape, making it far more convenient and robust than having loose or

exposed tape.

Disk storage or disc storage is a general category of storage mechanisms, in which data are

digitally recorded by various electronic, magnetic, optical, or mechanical methods on a surface

layer deposited of one or more planar, round and rotating platters. A disk drive is a device

implementing such a storage mechanism with fixed or removable media; with removable media the

device is usually distinguished from the media as in compact disc drive and the compact disc.

Notable types are the hard disk drive (which is today almost always use fixed media), the floppy

disk drive and its floppy disk, and various optical disc drives and associated media.

Musical and audio information was originally recorded by analog methods (see Sound recording

and reproduction). Similarly the first video disc used analog recording. Analog recording has been

mostly replaced by digital optical technology where the data is recorded in a digital format as

optical information.

Disk Storage

The first commercial disk storage device, that is the first commercial digital disk storage device,

was the IBM RAMAC 350 shipped in 1956 as a part of the IBM 305 RAMAC computing system.

Disk storage is now used in both computer storage and consumer electronic storage (e.g., audio CD

and video DVD).

The random-access, low-density storage of disks was developed to complement the already used

sequential-access high-density storage provided by magnetic tape. Vigorous innovation in disk

storage technology, coupled with less vigorous innovation in tape storage, has reduced the density

and cost per bit gap between disk and tape, reducing the importance of tape as a complement to

disk.

Today disk storage devices typically have a single head that moves across a disk surface; earlier

there were fixed head devices with multiple heads per surface but today they are no longer being

manufactured. Movable head devices store more data per sensor and usually more per area of the

medium. Fixed head devices avoid the seek time, while the head moves to the data.


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Disk drives are block storage devices. Each disk is divided into logical blocks (collection of

sectors). Blocks are addressed using their logical block addresses (LBA). Read from or writing to

disk happens at the granularity of blocks.

Originally the disk capacity was quite low and has been improved in one of several ways.

Improvements in mechanical design and manufacture allowed smaller and more accurate heads,

meaning that more tracks could be used on each of the platters. Advancements in data compression

methods created more information in each of the individual sectors, and this was instrumental in

allowing drives to store smaller units of data. sectors of data, the smallest unit stored, were reduced

and so less wasted space was created.

The drive stores data onto cylinders, heads and sectors. The sectors unit is the smallest size of data

to be stored in a Hard Disk Drive and each file will have many sectors units assigned to it. The

smallest entity in a CD is called a frame, which consists of 33 bytes and contains six complete 16-

bit stereo samples (two bytes two channels six samples = 24 bytes). The other nine bytes

consist of eight CIRC error-correction bytes and one subcode byte used for control and display.

The information is sent from the computer processor to the BIOS into a chip controlling the data

transfer. This is then sent out to the hard drive via a multi-wire connector. Once the data is

received onto the circuit board of the drive, it is translated and compressed into a format that the

individual drive can use to store onto the disk itself. The data is then passed to a chip on the circuit

board that controls the access to the drive. The drive is divided into sectors of data stored onto one

of the sides of one of the internal disks. In the picture opposite we have two disk, this gives us 4

sides.

The controller chip determines available free space by listing sectors in a table of used and unused

areas. This list is what determines where each part of a file is kept and where they are relative to

track, sector and disk. Different file systems use different types of addressing systems such as

FAT, NTFS, Joliet (ISO 9660) and UDF. Two copies of these lists are normally held and are used

to ensure data integrity. If a problem occurs a disk check can be run and it compares these two lists

to determine where the problem occurs and rebuilds the file structure from them. When a computer

drive is formatted the files are not erased but rather the lists are simply deleted. The drive hardware

will now treat all sectors as clean and overwrite them with new data.

The hardware on the drive tells the actuator arm where it is to go for the relevant track and the

compressed information is then sent down to the head which changes the physical properties,


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optically or magnetically for example, of each byte on the drive, thus storing the information. A

file is not stored in a linear manner, rather, it is held in the best way for quickest retrieval.

Mechanically, there are usually two types of motion: the constant rate rotation, which passes the

data of a track sequentially under a read head, and the radial (side-to-side) head motion or seek,

which selects the track. Rotation is faster than seek, so the logical blocks are related in simple

ways to the physical tracks.

HDD

HDDs (introduced in 1956 as data storage for an IBM accounting computer) were originally

developed for use with general purpose computers. During the 1990s, the need for large-scale,

reliable storage, independent of a particular device, led to the introduction of embedded systems

such as RAIDs, network attached storage (NAS) systems, and storage area network (SAN) systems

that provide efficient and reliable access to large volumes of data. In the 21st century, HDD usage

expanded into consumer applications such as camcorders, cellphones (e.g. the Nokia N91), digital

audio players, digital video players, digital video recorders, personal digital assistants and video

game consoles.

HDDs record data by magnetizing ferromagnetic material directionally, to represent either a 0 or a

1 binary digit. They read the data back by detecting the magnetization of the material. A typical

HDD design consists of a spindle that holds one or more flat circular disks called platters, onto

which the data are recorded. The platters are made from a non-magnetic material, usually

aluminum alloy or glass, and are coated with a thin layer of magnetic material, typically 1020 nm

in thickness for reference, standard copy paper is 0.070.18 millimetres (70,000180,000 nm)

thick with an outer layer of carbon for protection. Older disks used iron(III) oxide as the

magnetic material, but current disks use a cobalt-based alloy.

The platters are spun at very high speeds. Information is written to a platter as it rotates past

devices called read-and-write heads that operate very close (tens of nanometers in new drives) over

the magnetic surface. The read-and-write head is used to detect and modify the magnetization of

the material immediately under it. There is one head for each magnetic platter surface on the

spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc

(roughly radially) across the platters as they spin, allowing each head to access almost the entire


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surface of the platter as it spins. The arm is moved using a voice coil actuator or in some older

designs a stepper motor.

Data storage capacity

Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive.

Consequently, hard disk drives can store much more data than floppy disk drives and can access

and transmit them faster.

As of April 2010, the highest capacity consumer HDDs are 2 TB.

A typical "desktop HDD" stores between 120 GB and 2 TB (although rarely above 500 GB of data

based on US market data), rotates at 5,400 to 15,000 rpm, and has a media transfer rate of 0.5

Gbit/s or higher. (1 GB = 109 Byte; 1 Gbit/s = 109 bit/s)

The fastest enterprise HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media

transfer speeds above 1.6 Gbit/s. and a sustained transfer rate up to 1 Gbit/s. Drives running at

10,000 or 15,000 rpm use smaller platters to mitigate increased power requirements (as they have

less air drag) and therefore generally have lower capacity than the highest capacity desktop drives.

"Mobile HDDs", i.e., laptop HDDs, which are physically smaller than their desktop and enterprise

counterparts, tend to be slower and have lower capacity. A typical mobile HDD spins at either

4200 rpm, 5400 rpm, or 7200 rpm, with 5400 rpm being the most prominent. 7200 rpm drives tend

to be more expensive and have smaller capacities, while 4200 rpm models usually have very high

storage capacities. Because of physically smaller platter(s), mobile HDDs generally have lower

capacity than their larger desktop counterparts.

Magnetic Storage

Magnetic storage and magnetic recording are terms from engineering referring to the storage of

data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a

magnetizable material to store data and is a form of non-volatile memory. The information is

accessed using one or more read/write heads. As of 2009, magnetic storage media, primarily hard

disks, are widely used to store computer data as well as audio and video signals. In the field of

computing, the term magnetic storage is preferred and in the field of audio and video production,

the term magnetic recording is more commonly used. The distinction is less technical and more a


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matter of preference. Other examples of magnetic storage media include floppy disks, magnetic

recording tape, and magnetic stripes on credit cards.

Digital recording

Instead of creating a magnetization distribution in analog recording, digital recording only need

two stable magnetic states, which are the +Ms and -Ms on the hysteresis loop. Examples of digital

recording are floppy disks and HDDs. Since digital recording is the main process nowadays and

probably in the coming future, the details of magnetic recording will be discussed in the rest of the

project using the HDD as an example.

Magneto-optical recording

Magneto-optical recording writes/reads optically. When writing, the magnetic medium is heated

locally by a laser, which induces a rapid decrease of coercive field. Then, a small magnetic field

can be used to switch the magnetization. The reading process is based on magneto-optical Kerr

effect. The magnetic medium are typically amorphous R-FeCo thin film (R being a rare earth

element). Magneto-optical recording is not very popular. One famous example is Minidisc

developed by Sony.

Current usage

As of 2008, common uses of magnetic storage media are for computer data mass storage on hard

disks and the recording of analog audio and video works on analog tape. Since much of audio and

video production is moving to digital systems, the usage of hard disks is expected to increase at the

expense of analog tape. Digital tape and tape libraries are popular for the high capacity data storage

of archives and backups. Floppy disks see some marginal usage, particularly in dealing with older

computer systems and software. Magnetic storage is also widely used in some specific

applications, such as bank cheques (MICR) and credit/debit cards (mag stripes).

Future

A new type of magnetic storage, called Magnetoresistive Random Access Memory or MRAM, is

being produced that stores data in magnetic bits based on the tunnel magnetoresistance (TMR)

effect. Its advantage is non-volatility, low power usage, and good shock robustness. The 1st

generation that was developed was produced by Everspin Technologies, and utilized field induced

writing. The 2nd generation is being develped through two approaches: Thermal Assisted


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Switching (TAS) which is currently being developed by Crocus Technology, and Spin Torque

Transfer (STT) on which Crocus, Hynix, IBM, and several other companies are working.

However, with storage density and capacity orders of magnitude smaller than an HDD, MRAM is

useful in applications where moderate amounts of storage with a need for very frequent updates are

required, which flash memory cannot support due to its limited write endurance.

Optical disc drive

In computing, an optical disc drive (ODD) is a disk drive that uses laser light or electromagnetic

waves near the light spectrum as part of the process of reading or writing data to or from optical

discs. Some drives can only read from discs, but recent drives are commonly both readers and

recorders. Recorders are sometimes called burners or writers. Compact discs, DVDs, HD DVDs

and Blu-ray discs are common types of optical media which can be read and recorded by such

drives.

Optical disc drives are an integral part of stand-alone consumer appliances such as CD players,

DVD players and DVD recorders. They are also very commonly used in computers to read

software and consumer media distributed in disc form, and to record discs for archival and data

exchange. Optical drivesalong with flash memoryhave mostly displaced floppy disk drives

and magnetic tape drives for this purpose because of the low cost of optical media and the near-

ubiquity of optical drives in computers and consumer entertainment hardware.

Disc recording is generally restricted to small-scale backup and distribution, being slower and

more materially expensive per unit than the moulding process used to mass-manufacture pressed

discs.

3D optical data storage

Is the term given to any form of optical data storage in which information can be recorded and/or

read with three dimensional resolution (as opposed to the two dimensional resolution afforded, for

example, by CD).

This innovation has the potential to provide terabyte-level mass storage on DVD-sized disks. Data

recording and readback are achieved by focusing lasers within the medium. However, because of

the volumetric nature of the data structure, the laser light must travel through other data points

before it reaches the point where reading or recording is desired. Therefore, some kind of


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nonlinearity is required to ensure that these other data points do not interfere with the addressing of

the desired point.

No commercial product based on 3D optical data storage has yet arrived on the mass market,

although several companies are actively developing the technology and predict that it will become

available by the end of 2010.

3D optical data storage is related to (and competes with) holographic data storage. Traditional

examples of holographic storage do not address in the third dimension, and are therefore not

strictly "3D", but more recently 3D holographic storage has been realized by the use of

microholograms. Layer-selection multilayer technology (where a multilayer disc has layers that

can be individually activated e.g. electrically) is also closely related.

As an example, a prototypical 3D optical data storage system may use a disk that looks much like a

transparent DVD. The disc contains many layers of information, each at a different depth in the

media and each consisting of a DVD-like spiral track. In order to record information on the disc a

laser is brought to a focus at a particular depth in the media that corresponds to a particular

information layer. When the laser is turned on it causes a photochemical change in the media. As

the disc spins and the read/write head moves along a radius, the layer is written just as a DVD-R is

written. The depth of the focus may then be changed and another entirely different layer of

information written. The distance between layers may be 5 to 100 micrometers, allowing >100

layers of information to be stored on a single disc.

In order to read the data back (in this example), a similar procedure is used except this time instead

of causing a photochemical change in the media the laser causes fluorescence. This is achieved e.g.

by using a lower laser power or a different laser wavelength. The intensity or wavelength of the

fluorescence is different depending on whether the media has been written at that point, and so by

measuring the emitted light the data is read.

It should be noted that the size of individual chromophore molecules or photoactive color centers

is much smaller than the size of the laser focus (which is determined by the diffraction limit). The

light therefore addresses a large number (possibly even 109) of molecules at any one time, so the

medium acts as a homogeneous mass rather than a matrix structured by the positions of

chromophores.

Media form factor

Media for 3D optical data storage have been suggested in several form factors:


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Disc. A disc media offers a progression from CD/DVD, and allows reading and writing to be

carried out by the familiar spinning disc method.

Card. A credit card form factor media is attractive from the point of view of portability and

convenience, but would be of a lower capacity than a disc.

Crystal, Cube orSphere. Several science fiction writers have suggested small solids that store

massive amounts of information, and at least in principle this could be achieved with 3D optical

data storage.

Development issues

Despite the highly attractive nature of 3D optical data storage, the development of commercial

products has taken a significant length of time. This results from limited financial backing in the

field, as well as technical issues, including:

Destructive reading. Since both the reading and the writing of data are carried out with laser

beams, there is a potential for the reading process to cause a small amount of writing. In this case,

the repeated reading of data may eventually serve to erase it (this also happens in phase change

materials used in some DVDs). This issue has been addressed by many approaches, such as the use

of different absorption bands for each process (reading and writing), or the use of a reading method

that does not involve the absorption of energy.

Thermodynamic stability. Many chemical reactions that appear not to take place in fact happen

very slowly. In addition, many reactions that appear to have happened can slowly reverse

themselves. Since most 3D media are based on chemical reactions, there is therefore a risk that

either the unwritten points will slowly become written or that the written points will slowly revert

to being unwritten. This issue is particularly serious for the spiropyrans, but extensive research was

conducted to find more stable chromophores for 3D memories.

Media sensitivity. 2-photon absorption is a weak phenomenon, and therefore high power lasers are

usually required to produce it. Researchers typically use Ti-sapphire lasers or Nd:YAG lasers to

achieve excitation, but these instruments are not suitable for use in consumer products.

Holographic Data Storage


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Holographic data storage is a potential replacement technology in the area of high-capacity data

storage currently dominated by magnetic and conventional optical data storage. Magnetic and

optical data storage devices rely on individual bits being stored as distinct magnetic or optical

changes on the surface of the recording medium. Holographic data storage overcomes this

limitation by recording information throughout the volume of the medium and is capable of

recording multiple images in the same area utilizing light at different angles.

Additionally, whereas magnetic and optical data storage records information a bit at a time in a

linear fashion, holographic storage is capable of recording and reading millions of bits in parallel,

enabling data transfer rates greater than those attained by optical storage.

Holographic data storage captures information using an optical interference pattern within a thick,

photosensitive optical material. Light from a single laser beam is divided into two separate optical

patterns of dark and light pixels. By adjusting the reference beam angle, wavelength, or media

position, a multitude of holograms (theoretically, several thousand) can be stored on a single

volume. The theoretical limits for the storage density of this technique is approximately several

tens of Terabytes (1 terabyte = 1024 gigabytes) per cubic centimeter. In 2006, InPhase

Technologies published a white paper reporting an achievement of 500 Gb/in2. From this figure

we can deduce that a regular disk (with 4cm radius of writing area) could hold up to a maximum of

3895.6GB.The stored data is read through the reproduction of the same reference beam used to

create the hologram. The reference beams light is focused on the photosensitive material,

illuminating the appropriate interference pattern, the light diffracts on the interference pattern, and

projects the pattern onto a detector. The detector is capable of reading the data in parallel, over one

millions bits at once, resulting in the fast data transfer rate. Files on the holographic drive can be

accessed in less than 200 milliseconds.

Holographic data storage can provide companies a method to preserve and archive information.

The write-once, read many (WORM) approach to data storage would ensure content security,

preventing the information from being overwritten or modified. Manufacturers believe this

technology can provide safe storage for content without degradation for more than 50 years, far

exceeding current data storage options. Counterpoints to this claim point out the evolution of data

reader technology changes every ten years; therefore, being able to store data for 50100 years

would not matter if you could not read or access it.[3] However, a storage method that works very

well could be around longer before needing a replacement; plus, with the replacement, the


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possibility of backwards-compatibility exists, similar to how DVD technology is backwards-

compatible with CD technology.

Solid State Drive

A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent

data. An SSD emulates a hard disk drive interface, thus easily replacing it in most applications. An

SSD using SRAM or DRAM (instead of flash memory) is often called a RAM-drive, not to be

confused with a RAM disk. Recently, NAND based flash memory has become the standard for

most SSD's.

The original usage of the term "solid-state" (from solid-state physics) refers to the use of

semiconductor devices rather than electron tubes but, in the present context, has been adopted to

distinguish solid-state electronics from electromechanical devices. With no moving parts, solid-

state drives are less fragile than hard disks and are also silent (unless a cooling fan is used); as

there are no mechanical delays, they usually enjoy low access time and latency.

At Cebit 2009, OCZ demonstrated a 1 TB flash SSD using a PCI Express x8 interface. It achieves

a maximum write speed of 654MB/s and maximum read speed of 712MB/s.[4]

On March 2, 2009, Hewlett-Packard announced the HP StorageWorks IO Accelerator, the world's

first enterprise flash drive especially designed to attach directly to the PCI fabric of a blade server.

The mezzanine card, based on Fusion-io's ioDrive technology, serves over 100,000 IOPS and up to

800MB/s of bandwidth. HP provides the IO Accelerator in capacities of 80GB, 160GB and

320GB.

Advantages

Faster start-up because no spin-up is required.

Fast random access because there is no read/write head

Low read latency times for RAM drives. In applications where hard disk seeks are the

limiting factor, this results in faster boot and application launch times (see Amdahl's law).

Consistent read performance because physical location of data is irrelevant for SSDs.

File fragmentation has negligible effect.

Silent operation due to the lack of moving parts.

Low capacity flash SSDs have a low power consumption and generate little heat when in

use.


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High mechanical reliability, as the lack of moving parts almost eliminates the risk of

"mechanical" failure.

Ability to endure extreme shock, high altitude, vibration and extremes of temperature.This

makes SSDs useful for laptops, mobile computers, and devices that operate in extreme

conditions (flash).

For low-capacity SSDs, lower weight and size: although size and weight per unit storage

are still better for traditional hard drives, and microdrives allow up to 20 GB storage in a

CompactFlash form-factor. As of 2008 SSDs up to 256 GB are lighter than hard drives of

the same capacity.

Flash SSDs have twice the data density of HDDs (so far, with very recent and major

developments of improving SSD densities), even up to 1TB disks (currently more than 2TB

is atypical even for HDDs). One example of this advantage is that portable devices such as

a smartphone may hold as much as a typical person's desktop PC.

Failures occur less frequently while writing/erasing data, which means there is a lower

chance of irrecoverable data damage.

Defragmenting the SSD is unnecessary. Since SSDs are random access by nature and can

perform parallel reads on multiple sections of the drive (as opposed to a HDD, which

requires seek time for each fragment, assuming a single head assembly), a certain degree of

fragmentation is actually better for reads, and wear leveling intrinsically induces

fragmentation.[citation needed] In fact, defragmenting a SSD is harmful since it adds wear

to the SSD for no benefit.

Disadvantages

Flash-memory drives have limited lifetimes and will often wear out after 1,000,000 to

2,000,000 write cycles (1,000 to 10,000 per cell) for MLC, and up to 5,000,000 write

cycles (100,000 per cell) for SLC. Special file systems or firmware designs can mitigate

this problem by spreading writes over the entire device, called wear leveling. Wear leveling used on flash-based SSDs has security implications. For example,

encryption of existing unencrypted data on flash-based SSDs cannot be performed securely

due to the fact that wear leveling causes new encrypted drive sectors to be written to a

physical location different from their original locationdata remains unencrypted in the


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original physical location. It is also impossible to securely wipe files by overwriting their

content on flash-based SSDs.

As of early-2010, SSDs are still more expensive per gigabyte than hard drives. Whereas a

normal flash drive is US$2 per gigabyte, hard drives are around US$0.10 per gigabyte for

3.5", or US$0.20 for 2.5".

The capacity of SSDs is currently lower than that of hard drives. However, flash SSD

capacity is predicted to increase rapidly, with drives of 1 TB already released for enterprise

and industrial applications.

Asymmetric read vs. write performance can cause problems with certain functions where

the read and write operations are expected to be completed in a similar timeframe. SSDs

currently have a much slower write performance compared to their read performance.

Similarly, SSD write performance is significantly impacted by the availability of free,

programmable blocks. Previously written data blocks that are no longer in use can be

reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks

translates into reduced performance.

As a result of wear leveling and write combining, the performance of SSDs degrades with

use.

SATA-based SSDs generally exhibit much slower write speeds. As erase blocks on flash-

based SSDs generally are quite large (e.g. 0.5 - 1 megabyte),[8] they are far slower than

conventional disks during small writes (write amplification effect) and can suffer from

write fragmentation.[37] Modern PCIe SSDs however have much faster write speeds than

previously available.

DRAM-based SSDs (but not flash-based SSDs) require more power than hard disks, when

operating; they still use power when the computer is turned off, while hard disks do not.

Quality and performance

Quality and performance

SSD is a rapidly developing technology. A January 2009 review of the market by technology

reviewer Tom's Hardware concluded that comparatively few of the tested devices showed

acceptable I/O performance, with several disappointments,[45] and that Intel (who make their own

SSD chipset) still produces the best performing SSD drive as of this time; a view also echoed by


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Anandtech.[46] In particular, operations that require many small writes, such as log files, are

particularly badly affected on some devices, potentially causing the entire host system to freeze for

periods of up to one second at a time.

According to Anandtech, this is due to controller chip design issues with a widely used set of

components, and at least partly arises because most manufacturers are memory manufacturers

only, rather than full microchip design and fabrication businesses they often rebrand others'

products, inadvertently replicating their problems. Of the other manufacturers in the market,

Memoright, Mtron, OCZ, Samsung and Soliware were also named positively for at least some

areas of testing.

The overall conclusion by Tom's Hardware however, was that "none of the [non-Intel] drives were

really impressive. They all have significant weaknesses: usually either low I/O performance, poor

write throughput or unacceptable power consumption".

Performance of flash SSDs are difficult to benchmark. In a test done by Xssist, using IOmeter,

4KB RANDOM 70/30 RW, queue depth 4, the IOPS delivered by the Intel X25-E 64GB G1

started around 10000 IOPs, and dropped sharply after 8 minutes to 4000 IOPS, and continued to

decrease gradually for the next 42 minutes. IOPS vary between 3000 to 4000 from around the 50th

minutes onwards for the rest of the 8+ hours test run.

OCZ has recently unveiled OCZ Vertex 2 Pro which is currently the fastest MLC SSD drive with a

Sandforce Controller onboard performing more or less as the Intel X25-E series SSD drives

The Optical Storage Technology Association (OSTA)

Is an international trade association which promotes the use of recordable optical technologies and

products, and most notably it is responsible for the creation and maintenance of the UDF

specification. Representing more than 85 percent of worldwide writable optical product shipment's

manufacturers and resellers, it was incorporated in 1992.

In the autumn of 2007, OSTA spearheaded a campaign to encourage families and photographers to

back-up their digital photographs on compact discs. Since it is estimated that one out of seven

computer hard drives "crash" within the first year, OSTA believes it is dangerous to merely rely on

storing irreplaceable pictures on a hard drive alone. Optical discs (CD, DVD, BD), are an


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economical and reliable way to back up pictures and to make extra copies for greater protection

and to share pictures with others.

Digital Preservation

Digital preservation is the management of digital information over time. Preservation of digital

information is widely considered to require more constant and ongoing attention than preservation

of other media. This constant input of effort, time, and money to handle rapid technological and

organizational advance is considered the main stumbling block for preserving digital information.

Indeed, while we are still able to read our written heritage from several thousand years ago, the

digital information created merely a decade ago is in serious danger of being lost, creating a digital

Dark Age.

Digital preservation can therefore be seen as the set of processes and activities that ensure

continued access to information and all kinds of records, scientific and cultural heritage existing in

digital formats. This includes the preservation of materials resulting from digital reformatting, but

particularly information that is born-digital and has no analog counterpart. In the language of

digital imaging and electronic resources, preservation is no longer just the product of a program

but an ongoing process. In this regard the way digital information is stored is important in ensuring

its longevity. The long-term storage of digital information is assisted by the inclusion of

preservation metadata.

Digital preservation is defined as: long-term, error-free storage of digital information, with means

for retrieval and interpretation, for the entire time span the information is required for. Long-term

is defined as "long enough to be concerned with the impacts of changing technologies, including

support for new media and data formats, or with a changing user community. Long Term may

extend indefinitely"[2]. "Retrieval" means obtaining needed digital files from the long-term, error-

free digital storage, without possibility of corrupting the continued error-free storage of the digital

files. "Interpretation" means that the retrieved digital files, files that, for example, are of texts,

charts, images or sounds, are decoded and transformed into usable representations. This is often

interpreted as "rendering", i.e. making it available for a human to access. However, in many cases

it will mean able to be processed by computational means.

Why active preservation is necessary


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Society's heritage has been presented on many different materials, including stone, vellum,

bamboo, silk, paper and etc. Now a large quantity of information exists in digital forms, including

emails, blogs, social networking websites, national elections websites, web photo albums, and sites

which change their content over time. According to a report by the US Library of Congress, 44%

of the sites available on the internet in 1998 had vanished one year later[3].

The unique characteristic of digital forms makes it easy to create content and keep it up-to-date,

but at the same time brings many difficulties in the preservation of this content. Margaret

Hedstrom points out that "...digital preservation raises challenges of a fundamentally different

nature which are added to the problems of preserving traditional format materials."

The media on which digital contents are stored are more vulnerable to deterioration and

catastrophic loss than some analog media such as paper. While acid paper is prone to deterioration,

becoming brittle and yellowing with age, the deterioration may not become apparent for some

decades and progresses slowly. It remains possible to retrieve information without loss once

deterioration is noticed. Digital data recording media may deteriorate more rapidly and once the

deterioration starts, in most cases there may already be data loss. This characteristic of digital

forms leaves a very short time frame for preservation decisions and actions.

Strategies

In 2006, the Online Computer Library Center developed a four-point strategy for the long-term

preservation of digital objects that consisted of:

Assessing the risks for loss of content posed by technology variables such as commonly

used proprietary file formats and software applications.

Evaluating the digital content objects to determine what type and degree of format

conversion or other preservation actions should be applied.

Determining the appropriate metadata needed for each object type and how it is associated

with the objects.

Providing access to the content.

There are several additional strategies that individuals and organizations may use to actively

combat the loss of digital information.

Digital sustainability


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Digital sustainability encompasses a range of issues and concerns that contribute to the longevity

of digital information. Unlike traditional, temporary strategies and more permanent solutions,

digital sustainability implies a more active and continuous process. Digital sustainability

concentrates less on the solution and technology and more on building an infrastructure and

approach that is flexible with an emphasis on interoperability, continued maintenance and

continuous development. Digital sustainability incorporates activities in the present that will

facilitate access and availability in the future.

Digital preservation standards

To standardize digital preservation practice and provide a set of recommendations for preservation

program implementation, the Reference Model for an Open Archival Information System (OAIS)

was developed. The reference model (ISO 14721:2003) includes the following responsibilities that

an OAIS archive must abide by:

Negotiate for and accept appropriate information from information Producers.

Obtain sufficient control of the information provided to the level needed to ensure Long-

Term Preservation.

Determine, either by itself or in conjunction with other parties, which communities should

become the Designated Community and, therefore, should be able to understand the

information provided.

Ensure that the information to be preserved is Independently Understandable to theDesignated Community. In other words, the community should be able to understand the

information without needing the assistance of the experts who produced the information.

Follow documented policies and procedures which ensure that the information is preserved

against all reasonable contingencies, and which enable the information to be disseminated

as authenticated copies of the original, or as traceable to the original.

Make the preserved information available to the Designated Community

Digital sound preservation standards

In January 2004, the Council on Library and Information Resources (CLIR) hosted a roundtable

meeting of audio experts discussing best practices, which culminated in a report delivered March

2006. This report investigated procedures for reformatting sound from analog to digital,

summarizing discussions and recommendations for best practices for digital preservation.


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Participants made a series of 15 recommendations for improving the practice of analog audio

transfer for archiving:

Develop core competencies in audio preservation engineering. Participants noted with

concern that the number of experts qualified to transfer older recordings is shrinking and

emphasized the need to find a way to ensure that the technical knowledge of these experts

can be passed on.

Develop arrangements among smaller institutions that allow for cooperative buying of

esoteric materials and supplies.

Pursue a research agenda for magnetic-tape problems that focuses on a less destructive

solution for hydrolysis than baking, relubrication of acetate tapes, and curing of cupping.

Develop guidelines for the use of automated transfer of analog audio to digital preservation

copies.

Develop a web-based clearinghouse for sharing information on how archives can develop

digital preservation transfer programs.

Carry out further research into nondestructive playback of broken audio discs.

Develop a flowchart for identifying the composition of various types of audio discs and

tapes.

Develop a reference chart of problematic media issues.

Collate relevant audio engineering standards from organizations.

Research safe and effective methods for cleaning analog tapes and discs.

Develop a list of music experts who could be consulted for advice on transfer of specific

types of musical content (e.g., determining the proper key so that correct playback speed

can be established).

Research the life expectancy of various audio formats.

Establish regional digital audio repositories.

Cooperate to develop a common vocabulary within the field of audio preservation.

Investigate the transfer of technology from such fields as chemistry and materials science

to various problems in audio preservation.


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Analog-to-digital converter

An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a device which converts

continuous signals to discrete digital numbers. The reverse operation is performed by a digital-to-

analog converter (DAC).

Typically, an ADC is an electronic device that converts an input analog voltage (or current) to a

digital number proportional to the magnitude of the voltage or current. However, some non-

electronic or only partially electronic devices, such as rotary encoders, can also be considered

ADCs. The digital output may use different coding schemes, such as binary, Gray code or two's

complement binary.

Application to music recording

ADCs are integral to current music reproduction technology. Since much music production is done

on computers, when an analog recording is used, an ADC is needed to create the PCM data stream

that goes onto a compact disc or digital music file.

The current crop of AD converters utilized in music can sample at rates up to 192 kilohertz. High

bandwidth headroom allows the use of cheaper or faster anti-aliasing filters of less severe filtering

slopes. The proponents of oversampling assert that such shallower anti-aliasing filters produce less

deleterious effects on sound quality, exactly because of their gentler slopes. Others prefer entirely

filterless AD conversion, arguing that aliasing is less detrimental to sound perception than pre-

conversion brickwall filtering. Considerable literature exists on these matters, but commercial

considerations often play a significant role. Most[citation needed] high-profile recording studios

record in 24-bit/192-176.4 kHz PCM or in DSD formats, and then downsample or decimate the

signal for Red-Book CD production (44.1 kHz or at 48 kHz for commonly used for radio/TV

broadcast applications).

Digital Audio

Digital audio uses digital signals for sound reproduction. This includes analog-to-digital

conversion, digital-to-analog conversion, storage, and transmission. In effect, the system

commonly referred to as digital is in fact a discrete-time, discrete-level analog of a previous

electrical analog. While modern systems can be quite subtle in their methods, the primary

usefulness of a digital system is that, due to its discrete (in both time and amplitude) nature, signals

can be corrected, once they are digital, without loss, and the digital signal can be reconstituted. The


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discreteness in both time and amplitude is key to this reconstitution, which is unavailable for a

signal in which time or amplitude or both are continuous. While the hybrid systems (part discrete,

part continuous) exist, they are no longer used for new modern systems.

Digital audio has emerged because of its usefulness in the recording, manipulation, mass-

production, and distribution of sound. Modern distribution of music across the Internet via on-line

stores depends on digital recording and digital compression algorithms. Distribution of audio as

data files rather than as physical objects has significantly reduced the cost of distribution.

From the wax cylinder to the compact cassette, analog audio music storage and reproduction have

been based on the same principles upon which human hearing are based. In an analog audio

system, sounds begin as physical waveforms in the air, are transformed into an electrical

representation of the waveform, via a transducer (for example, a microphone), and are stored or

transmitted. To be re-created into sound, the process is reversed, through amplification and then

conversion back into physical waveforms via a loudspeaker. Although its nature may change,

analog audio's fundamental wave-like characteristics remain the same during its storage,

transformation, duplication, and amplification.

Analog audio signals are susceptible to noise and distortion, unavoidable due to the innate

characteristics of electronic circuits and associated devices. In the case of purely analog recording

and reproduction, numerous opportunities for the introduction of noise and distortion exist

throughout the entire process. When audio is digitized, distortion and noise are introduced only by

the stages that precede conversion to digital format, and by the stages that follow conversion back

to analog.

The digital audio chain begins when an analog audio signal is first sampled, and then (for pulse-

code modulation, the usual form of digital audio) converted into binary signalson/off pulses

which are stored as binary electronic, magnetic, or optical signals, rather than as continuous time,

continuous level electronic or electromechanical signals. This signal may then further encoded to

combat any errors that might occur in the storage or transmission of the signal, however this

encoding is for the purpose of error correction, and is not strictly part of the digital audio process.

This "channel coding" is essential to the ability of broadcast or recorded digital system to avoid

loss of bit accuracy. The discrete time and level of the binary signal allow a decoder to recreate the

analog signal upon replay. An example of a channel code is Eight to Fourteen Bit Modulation as

used in the audio compact disc.


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Conversion process

A digital audio signal starts with an analog-to-digital converter (ADC) that converts an analog

signal to a digital signal. The ADC runs at a sampling rate and converts at a known bit resolution.

For example, CD audio has a sampling rate of 44.1 kHz (44,100 samples per second) and 16-bit

resolution for each channel (stereo). If the analog signal is not already bandlimited then an anti-

aliasing filter is necessary before conversion, to prevent aliasing in the digital signal. (Aliasing

occurs when frequencies above the Nyquist frequency have not been band limited, and instead

appear as audible artifacts in the lower frequencies).

Some audio signals such as those created by digital synthesis originate entirely in the digital

domain, in which case analog to digital conversion does not take place.

After being sampled with the ADC, the digital signal may then be altered in a process which is

called digital signal processing where it may be filtered or have effects applied. The digital audio

signal may then be stored or transmitted. Digital audio storage can be on a CD, a digital audio

player, a hard drive, USB flash drive, CompactFlash, or any other digital data storage device.

Audio data compression techniques such as MP3, Advanced Audio Coding, Ogg Vorbis, or

FLAC are commonly employed to reduce the file size. Digital audio can be streamed to other

devices.

The last step for digital audio is to be converted back to an analog signal with a digital-to-analog

converter (DAC). Like ADCs, DACs run at a specific sampling rate and bit resolution but through

the processes of oversampling, upsampling, and downsampling, this sampling rate may not be the

same as the initial sampling rate.

Digital Library

A digital library is a library in which collections are stored in digital formats (as opposed to print,

microform, or other media) and accessible by computers. The digital content may be stored locally,

or accessed remotely via computer networks. A digital library is a type of information retrieval

system.

The DELOS Digital Library Reference Model defines a digital library as:


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An organization, which might be virtual, that comprehensively collects, manages and preserves for

the long term rich digital content, and offers to its user communities specialized functionality on

that content, of measurable quality and according to codified policies.

The first use of the term digital library in print may have been in a 1988 report to the Corporation

for National Research Initiatives[3] The term digital libraries was first popularized by the

NSF/DARPA/NASA Digital Libraries Initiative in 1994.[4] These draw heavily on As We May

Think by Vannevar Bush in 1945, which set out a vision not in terms of technology, but user

experience. The term virtual library was initially used interchangeably with digital library, but is

now primarily used for libraries that are virtual in other senses (such as libraries which aggregate

distributed content). Wikiversity has learning materials about Curriculum on Digital Libraries.

A distinction is often made between content that was created in a digital format, known as born-

digital, and information that has been converted from a physical medium, e.g., paper, by digitizing.

The term hybrid library is sometimes used for libraries that have both physical collections and

digital collections. For example, American Memory is a digital library within the Library of

Congress. Some important digital libraries also serve as long term archives, for example, the ePrint

arXiv, and the Internet Archive.

Academic repositories

Many academic libraries are actively involved in building institutional repositories of the

institution's books, papers, theses, and other works which can be digitized or were 'born digital'.

Many of these repositories are made available to the general public with few restrictions, in

accordance with the goals of open access, in contrast to the publication of research in commercial

journals, where the publishers often limit access rights. Institutional, truly free, and corporate

repositories are sometimes referred to as digital libraries.

Digital archives

Physical archives differ from physical libraries in several ways. Traditionally, archives were

defined as:

Containing primary sources of information (typically letters and papers directly produced

by an individual or organization) rather than the secondary sources found in a library

(books, periodicals, etc);

Having their contents organized in groups rather than individual items;


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Having unique contents.

The technology used to create digital libraries has been even more revolutionary for archives since

it breaks down the second and third of these general rules. In other words, "digital archives" or

"online archives" will still generally contain primary sources, but they are likely to be described

individually rather than (or in addition to) in groups or collections, and because they are digital

their contents are easily reproducible and may indeed have been reproduced from elsewhere. The

Oxford Text Archive is generally considered to be the oldest digital archive of academic physical

primary source materials.

Leaders in the field

Project Gutenberg, Google Book Search, Internet Archive, Cornell University, The Library

of Congress World Digital Library, The Digital Library at the University of Michigan, the

Greenstone Digital Library at the University of Waikato, and Carnegie Mellon University's

Million Book Project are considered leaders in the field of digital library creation and

management.

The future

Large scale digitization projects are underway at Google, the Million Book Project, and Internet

Archive. With continued improvements in book handling and presentation technologies such as

optical character recognition and ebooks, and development of alternative depositories and business

models, digital libraries are rapidly growing in popularity as demonstrated by Google, Yahoo!, andMSN's efforts. Just as libraries have ventured into audio and video collections, so have digital

libraries such as the Internet Archive.

According to Larry Lannom, Director of Information Management Technology at the nonprofit

Corporation for National Research Initiatives, all the problems associated with digital libraries are

wrapped up in archiving. He goes on to state, If in 100 years people can still read your article,

well have solved the problem. Daniel Akst, author of The Webster Chronicle, proposes that the

future of librariesand of informationis digital. Peter Lyman and Hal Varian, information

scientists at the University of California, Berkeley, estimate that the worlds total yearly

production of print, film, optical, and magnetic content would require roughly 1.5 billion gigabytes

of storage. Therefore, they believe that soon it will be technologically possible for an average

person to access virtually all recorded information.

Advantages


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The advantages of digital libraries as a means of easily and rapidly accessing books, archives and

images of various types are now widely recognized by commercial interests and public bodies

alike. Traditional libraries are limited by storage space; digital libraries have the potential to store

much more information, simply because digital information requires very little physical space to

contain it. As such, the cost of maintaining a digital library is much lower than that of a traditional

library. A traditional library must spend large sums of money paying for staff, book maintenance,

rent, and additional books. Digital libraries may reduce or, in some instances, do away with these

fees. Both types of library require cataloguing input to allow users to locate and retrieve material.

Digital libraries may be more willing to adopt innovations in technology providing users with

improvements in electronic and audio book technology as well as presenting new forms of

communication such as wikis and blogs; conventional libraries may consider that providing online

access to their OPAC catalogue is sufficient. An important advantage to digital conversion is

increased accessibility to users. They also increase availability to individuals who may not be

traditional patrons of a library, due to geographic location or organizational affiliation.

No physical boundary. The user of a digital library need not to go to the library physically;

people from all over the world can gain access to the same information, as long as an

Internet connection is available.

Round the clock availability. A major advantage of digital libraries is that people can gain

access to the information at any time, night or day. Multiple access. The same resources can be used simultaneously by a number of

institutions and patrons. This may not be the case for copyrighted material: a library may

have a license for "lending out" only one copy at a time; this is achieved with a system of

digital rights management where a resource can become inaccessible after expiration of the

lending period or after the lender chooses to make it inaccessible (equivalent to returning

the resource).

Information retrieval. The user is able to use any search term (word, phrase, title, name,

subject) to search the entire collection. Digital libraries can provide very user-friendly

interfaces, giving clickable access to its resources.

Preservation and conservation. Digitization is not a long-term preservation solution for

physical collections, but does succeed in providing access copies for materials that would

otherwise fall to degradation from repeated use. Digitized collections and born-digital


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objects pose many preservation and conservation concerns that analog materials do not.

Please see the following "Problems" section of this page for examples.

Space. Whereas traditional libraries are limited by storage space, digital libraries have the

potential to store much more information, simply because digital information requires very

little physical space to contain them and media storage technologies are more affordable

than ever before.

Added value. Certain characteristics of objects, primarily the quality of images, may be

improved. Digitization can enhance legibility and remove visible flaws such as stains and

discoloration.

The work needed to ensure that digital content is maintained and accessible into the future is

beginning to be addressed.

Technological standards change over time and forward migration must be a constant consideration

of every library. Migration is a means of transferring an unstable digital object to another more

stable format, operating system, or programming language.[14] Migration allows the ability to

retrieve and display digital objects that are in danger of becoming extinct. This is a rather

successful short-term solution for the problem of aging and obsolete digital formats, but with the

ever-changing nature of computer technologies, migration becomes this never-ending race to

transfer digital objects to new and more stable formats. Migration is also flawed in the sense that

when the digital files are being transferred, the new platform may not be able to capture the fullintegrity of the original object.[15] There are countless artifacts sitting in libraries all over the

world that are essentially useless because the technology required to access the source is obsolete.

In addition to obsolescence, there are rising costs that result from continually replacing the older

technologies. This issue can dominate preservation policy and may put more focus on instant user

access in place of physical preservation.

Copyright and licensing

Some people have criticized that digital libraries are hampered by copyright law, because works

cannot be shared over different periods of time in the manner of a traditional library. The

republication of material on the Web by libraries may require permission from rights holders, and

there is a conflict of interest between them and publishers who may wish to create Web versions of

their content for commercial purposes.


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There is a dilution of responsibility that occurs as a result of the spread-out nature of digital

resources. Complex intellectual property matters may become involved since digital material isn't

always owned by a library.[17] The content is, in many cases, public domain or self-generated

content only. Some digital libraries, such as Project Gutenberg, work to digitize out-of-copyright

works and make them freely available to the public. An estimate of the number of distinct books

still existent in library catalogues from 2000BC to 1960, has been made.

The Fair Use Provisions (17 USC 107) under copyright law provide specific guidelines under

which circumstances libraries are allowed to copy digital resources. Four factors that constitute fair

use are purpose of use, nature of the work, market impact, and amount or substantiality used.

Some digital libraries acquire a license to "lend out" their resources. This may involve the

restriction of lending out only one copy at a time for each license, and applying a system of digital

rights management for this purpose.

Sites visited or to be visited:

1. http://en.wikipedia.org/wiki/Digitizing

2. http://en.wikipedia.org/wiki/Digital_Data_Storage

3. http://en.wikipedia.org/wiki/Data_storage_device

4. http://en.wikipedia.org/wiki/Tape_drive

5. http://en.wikipedia.org/wiki/Disk_storage

6. http://en.wikipedia.org/wiki/Hard_disk_drive

7. http://en.wikipedia.org/wiki/Magnetic_storage

8. http://en.wikipedia.org/wiki/Optical_disc_drive

9. http://en.wikipedia.org/wiki/3D_optical_data_storage

10.http://en.wikipedia.org/wiki/HDSS

11.http://en.wikipedia.org/wiki/Optical_Storage_Technology_Association

12.http://en.wikipedia.org/wiki/Hologram

13.http://en.wikipedia.org/wiki/Holographic_data_storage

14.http://en.wikipedia.org/wiki/Solid-state_drive
http://en.wikipedia.org/wiki/Digitizinghttp://en.wikipedia.org/wiki/Digital_Data_Storagehttp://en.wikipedia.org/wiki/Data_storage_devicehttp://en.wikipedia.org/wiki/Tape_drivehttp://en.wikipedia.org/wiki/Disk_storagehttp://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Magnetic_storagehttp://en.wikipedia.org/wiki/Optical_disc_drivehttp://en.wikipedia.org/wiki/3D_optical_data_storagehttp://en.wikipedia.org/wiki/HDSShttp://en.wikipedia.org/wiki/Optical_Storage_Technology_Associationhttp://en.wikipedia.org/wiki/Hologramhttp://en.wikipedia.org/wiki/Holographic_data_storagehttp://en.wikipedia.org/wiki/Solid-state_drivehttp://en.wikipedia.org/wiki/Digitizinghttp://en.wikipedia.org/wiki/Digital_Data_Storagehttp://en.wikipedia.org/wiki/Data_storage_devicehttp://en.wikipedia.org/wiki/Tape_drivehttp://en.wikipedia.org/wiki/Disk_storagehttp://en.wikipedia.org/wiki/Hard_disk_drivehttp://en.wikipedia.org/wiki/Magnetic_storagehttp://en.wikipedia.org/wiki/Optical_disc_drivehttp://en.wikipedia.org/wiki/3D_optical_data_storagehttp://en.wikipedia.org/wiki/HDSShttp://en.wikipedia.org/wiki/Optical_Storage_Technology_Associationhttp://en.wikipedia.org/wiki/Hologramhttp://en.wikipedia.org/wiki/Holographic_data_storagehttp://en.wikipedia.org/wiki/Solid-state_drive


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15.http://en.wikipedia.org/wiki/Computer_data_storage

16.http://en.wikipedia.org/wiki/Digital_Preservation

17.http://en.wikipedia.org/wiki/Audio_format

18.http://en.wikipedia.org/wiki/Disk_format

19.http://en.wikipedia.org/wiki/Audio_file_format

20.http://en.wikipedia.org/wiki/Analog_to_digital_converter

21.http://en.wikipedia.org/wiki/Digital_audio

22.http://en.wikipedia.org/wiki/Digital_Library

23.http://en.wikipedia.org/wiki/Super_Audio_CD

24.http://en.wikipedia.org/wiki/Digital_preservation

25.http://www.digitalpreservationeurope.eu/

26.http://www.nla.gov.au/padi/

27.http://www.content-conversion.com/ro/welcome.htm

28.http://www.dlib.org/dlib/january00/01hodge.html

29.http://www.ica.org/en/2010/04/28/8th-european-conference-digital-archiving-

geneva-2010

30.http://en.wikipedia.org/wiki/Digital_Audio_Tape
http://en.wikipedia.org/wiki/Solid-state_drivehttp://en.wikipedia.org/wiki/Computer_data_storagehttp://en.wikipedia.org/wiki/Digital_Preservationhttp://en.wikipedia.org/wiki/Audio_formathttp://en.wikipedia.org/wiki/Disk_formathttp://en.wikipedia.org/wiki/Audio_file_formathttp://en.wikipedia.org/wiki/Analog_to_digital_converterhttp://en.wikipedia.org/wiki/Digital_audiohttp://en.wikipedia.org/wiki/Digital_Libraryhttp://en.wikipedia.org/wiki/Super_Audio_CDhttp://en.wikipedia.org/wiki/Digital_preservationhttp://www.digitalpreservationeurope.eu/http://www.nla.gov.au/padi/http://www.content-conversion.com/ro/welcome.htmhttp://www.dlib.org/dlib/january00/01hodge.htmlhttp://www.dlib.org/dlib/january00/01hodge.htmlhttp://www.ica.org/en/2010/04/28/8th-european-conference-digital-archiving-geneva-2010http://www.ica.org/en/2010/04/28/8th-european-conference-digital-archiving-geneva-2010http://en.wikipedia.org/wiki/Digital_Audio_Tapehttp://en.wikipedia.org/wiki/Computer_data_storagehttp://en.wikipedia.org/wiki/Digital_Preservationhttp://en.wikipedia.org/wiki/Audio_formathttp://en.wikipedia.org/wiki/Disk_formathttp://en.wikipedia.org/wiki/Audio_file_formathttp://en.wikipedia.org/wiki/Analog_to_digital_converterhttp://en.wikipedia.org/wiki/Digital_audiohttp://en.wikipedia.org/wiki/Digital_Libraryhttp://en.wikipedia.org/wiki/Super_Audio_CDhttp://en.wikipedia.org/wiki/Digital_preservationhttp://www.digitalpreservationeurope.eu/http://www.nla.gov.au/padi/http://www.content-conversion.com/ro/welcome.htmhttp://www.dlib.org/dlib/january00/01hodge.htmlhttp://www.ica.org/en/2010/04/28/8th-european-conference-digital-archiving-geneva-2010http://www.ica.org/en/2010/04/28/8th-european-conference-digital-archiving-geneva-2010http://en.wikipedia.org/wiki/Digital_Audio_Tape

Documents

Manual on Digital Storage