The Information Age is a historic period in the 21st century characterized by the rapid shift from traditional industry that the Industrial Revolution brought through industrialization, to an economy based on information technology. The onset of the Information Age can be associated with William Shockley, Walter Houser Brattain and John Bardeen, the inventors and engineers behind the first transistors, revolutionising modern technologies. With the Digital Revolution, just as the Industrial Revolution marked the onset of the Industrial Age; the definition of what "digital" means continues to change over time as new technologies, user devices, methods of interaction with other humans and devices enter the domain of research and market launch. During the Information Age, digital industry shapes a knowledge-based society surrounded by a high-tech global economy that exerts influence on how the manufacturing and service sectors operate in an efficient and convenient way. In a commercialized society, the information industry can allow individuals to explore their personalized needs, therefore simplifying the procedure of making decisions for transactions and lowering costs both for producers and for buyers.
This is accepted overwhelmingly by participants throughout the entire economic activities for efficacy purposes, new economic incentives would be indigenously encouraged, such as the knowledge economy. The Information Age formed by capitalizing on computer microminiaturization advances; this evolution of technology in daily life and social organization has led to the modernization of information and communication processes becoming the driving force of social evolution. Library expansion was calculated in 1945 by Fremont Rider to double in capacity every 16 years if sufficient space were made available, he advocated replacing bulky, decaying printed works with miniaturized microform analog photographs, which could be duplicated on-demand for library patrons or other institutions. He did not foresee the digital technology that would follow decades to replace analog microform with digital imaging and transmission media. Automated lossless digital technologies allowed vast increases in the rapidity of information growth.
Moore's law, formulated around 1965, calculated that the number of transistors in a dense integrated circuit doubles every two years. The proliferation of the smaller and less expensive personal computers and improvements in computing power by the early 1980s resulted in sudden access to and the ability to share and store information for increasing numbers of workers. Connectivity between computers within companies led to the ability of workers at different levels to access greater amounts of information; the world's technological capacity to store information grew from 2.6 exabytes in 1986 to 15.8 in 1993, over 54.5 in 2000, to 295 exabytes in 2007. This is the informational equivalent to less than one 730-MB CD-ROM per person in 1986 4 CD-ROM per person of 1993, 12 CD-ROM per person in the year 2000, 61 CD-ROM per person in 2007, it is estimated that the world's capacity to store information has reached 5 zettabytes in 2014. This is the informational equivalent of 4,500 stacks of printed books from the earth to the sun.
The world's technological capacity to receive information through one-way broadcast networks was 432 exabytes of information in 1986, 715 exabytes in 1993, 1.2 zettabytes in 2000, 1.9 zettabytes in 2007. The world's effective capacity to exchange information through two-way telecommunication networks was 281 petabytes of information in 1986, 471 petabytes in 1993, 2.2 exabytes in 2000, 65 exabytes in 2007. In the 1990s, the spread of the Internet caused a sudden leap in access to and ability to share information in businesses and homes globally. Technology was developing so that a computer costing $3000 in 1997 would cost $2000 two years and $1000 the following year; the world's technological capacity to compute information with humanly guided general-purpose computers grew from 3.0 × 108 MIPS in 1986, to 4.4 × 109 MIPS in 1993, 2.9 × 1011 MIPS in 2000 to 6.4 × 1012 MIPS in 2007. An article in the recognized Journal Trends in Ecology and Evolution reports that by now digital technology "has vastly exceeded the cognitive capacity of any single human being and has done so a decade earlier than predicted.
In terms of capacity, there are two measures of importance: the number of operations a system can perform and the amount of information that can be stored. The number of synaptic operations per second in a human brain has been estimated to lie between 10^15 and 10^17. While this number is impressive in 2007 humanity's general-purpose computers were capable of performing well over 10^18 instructions per second. Estimates suggest. On a per capita basis, this is matched by current digital storage". Information and Communication Technology—computers, computerized machinery, fiber optics, communication satellites and other ICT tools—became a significant part of the economy. Microcomputers were developed and many businesses and industries were changed by ICT. Nicholas Negroponte captured the essence of these changes in his 1995 book, Being Digital
Data fusion is the process of integrating multiple data sources to produce more consistent and useful information than that provided by any individual data source. Data fusion processes are categorized as low, intermediate, or high, depending on the processing stage at which fusion takes place. Low-level data fusion combines several sources of raw data to produce new raw data; the expectation is that fused data is more synthetic than the original inputs. For example, sensor fusion is known as data fusion and is a subset of information fusion. Humans are a prime example of Data Fusion; as humans, we rely on our senses such as our Vision, Taste and Physical Movement. A combination of all these senses combine on a daily basis to help us in performing most if not all tasks in our day to day lives; that in itself is a prime example of data fusion. We rely on a fusion of smelling and touching food to ensure it is edible or not. We rely on our sight and our ability to hear and control movement of our body to walk or drive and perform most tasks in our lives.
In all these cases, the Brain controls what we need to do next. Our brain relies on a fusion of data gathered from the aforementioned senses. In the geospatial domain, data fusion is synonymous with data integration. In these applications, there is a need to combine diverse data sets into a unified data set which includes all of the data points and time steps from the input data sets; the fused data set is different from a simple combined superset in that the points in the fused data set contain attributes and metadata which might not have been included for these points in the original data set. A simplified example of this process is shown below where data set "α" is fused with data set β to form the fused data set δ. Data points in set "α" have spatial coordinates X and Y and attributes A1 and A2. Data points in set β have spatial coordinates X and Y and attributes B1 and B2; the fused data set attributes. In a simple case where all attributes are uniform across the entire analysis domain, the attributes may be assigned: M?, N?, Q?, R? to M, N, Q, R.
In a real application, attributes are not uniform and some type of interpolation is required to properly assign attributes to the data points in the fused set. In a much more complicated application, marine animal researchers use data fusion to combine animal tracking data with bathymetric, sea surface temperature and animal habitat data to examine and understand habitat utilization and animal behavior in reaction to external forces such as weather or water temperature; each of these data sets exhibit a different spatial grid and sampling rate so a simple combination would create erroneous assumptions and taint the results of the analysis. But through the use of data fusion, all data and attributes are brought together into a single view in which a more complete picture of the environment is created; this enables scientists to identify key locations and times and form new insights into the interactions between the environment and animal behaviors. In the figure at right, rock lobsters are studied off the coast of Tasmania.
Dr. Hugh Pederson of the University of Tasmania used data fusion software to fuse southern rock lobster tracking data with bathymetry and habitat data to create a unique 4D picture of rock lobster behavior. In applications outside of the geospatial domain, differences in the usage of the terms Data integration and Data fusion apply. In areas such as business intelligence, for example, data integration is used to describe the combining of data, whereas data fusion is integration followed by reduction or replacement. Data integration might be viewed as set combination wherein the larger set is retained, whereas fusion is a set reduction technique with improved confidence. In the mid-1980s, the Joint Directors of Laboratories formed the Data Fusion Subpanel. With the advent of the World Wide Web, data fusion thus included data and information fusion; the JDL/DFIG introduced a model of data fusion. The six levels with the Data Fusion Information Group model are: Level 0: Source Preprocessing/subject Assessment Level 1: Object Assessment Level 2: Situation Assessment Level 3: Impact Assessment Level 4: Process Refinement Level 5: User Refinement Although the JDL Model is still in use today, it is criticized for its implication that the levels happen in order and for its lack of adequate representation of the potential for a human-in-the-loop.
The DFIG model explored the implications of situation awareness, user refinement, mission management. Despite these shortcomings, the JDL/DFIG models are useful for visualizing the data fusion process, facilitating discussion and common understanding, important for systems-level information fusion design. Geospatial information systems Soil mapping Business intelligence Oceanography Discovery science Business performance management Intelligent transport systems Loyalty card Cheminformatics Quantitative structure-activity relationship Bioinformatics Intelligence services Wireless sensor networks Biometrics The data from the different sensing technologies can be combined in intelligent ways to determine the traffic state accurately. A Data fusion based approach that utilizes the road side collected acoustic and sensor data has been shown to combine the advantages of the different individual methods. In many cases, geog
A CD-ROM is a pre-pressed optical compact disc that contains data. Computers can read—but not write to or erase—CD-ROMs, i.e. it is a type of read-only memory. During the 1990s, CD-ROMs were popularly used to distribute software and data for computers and fourth generation video game consoles; some CDs, called enhanced CDs, hold both computer data and audio with the latter capable of being played on a CD player, while data is only usable on a computer. The CD-ROM format was developed by Japanese company Denon in 1982, it was an extension of Compact Disc Digital Audio, adapted the format to hold any form of digital data, with a storage capacity of 553 MiB. CD-ROM was introduced by Denon and Sony at a Japanese computer show in 1984; the Yellow Book is the technical standard. One of a set of color-bound books that contain the technical specifications for all CD formats, the Yellow Book, standardized by Sony and Philips in 1983, specifies a format for discs with a maximum capacity of 650 MiB. CD-ROMs are identical in appearance to audio CDs, data are stored and retrieved in a similar manner.
Discs are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminium to make a reflective surface. The most common size of CD-ROM is 120 mm in diameter, though the smaller Mini CD standard with an 80 mm diameter, as well as shaped compact discs in numerous non-standard sizes and molds, are available. Data is stored on the disc as a series of microscopic indentations. A laser is shone onto the reflective surface of the disc to read the pattern of lands; because the depth of the pits is one-quarter to one-sixth of the wavelength of the laser light used to read the disc, the reflected beam's phase is shifted in relation to the incoming beam, causing destructive interference and reducing the reflected beam's intensity. This is converted into binary data. Several formats are used for data stored on compact discs, known as the Rainbow Books; the Yellow Book, published in 1988, defines the specifications for CD-ROMs, standardized in 1989 as the ISO/IEC 10149 / ECMA-130 standard.
The CD-ROM standard builds on top of the original Red Book CD-DA standard for CD audio. Other standards, such as the White Book for Video CDs, further define formats based on the CD-ROM specifications; the Yellow Book itself is not available, but the standards with the corresponding content can be downloaded for free from ISO or ECMA. There are several standards that define how to structure data files on a CD-ROM. ISO 9660 defines the standard file system for a CD-ROM. ISO 13490 is an improvement on this standard which adds support for non-sequential write-once and re-writeable discs such as CD-R and CD-RW, as well as multiple sessions; the ISO 13346 standard was designed to address most of the shortcomings of ISO 9660, a subset of it evolved into the UDF format, adopted for DVDs. The bootable CD specification was issued in January 1995, to make a CD emulate a hard disk or floppy disk, is called El Torito. Data stored on CD-ROMs follows the standard CD data encoding techniques described in the Red Book specification.
This includes cross-interleaved Reed–Solomon coding, eight-to-fourteen modulation, the use of pits and lands for coding the bits into the physical surface of the CD. The structures used to group data on a CD-ROM are derived from the Red Book. Like audio CDs, a CD-ROM sector contains 2,352 bytes of user data, composed of 98 frames, each consisting of 33-bytes. Unlike audio CDs, the data stored in these sectors corresponds to any type of digital data, not audio samples encoded according to the audio CD specification. To structure and protect this data, the CD-ROM standard further defines two sector modes, Mode 1 and Mode 2, which describe two different layouts for the data inside a sector. A track inside a CD-ROM only contains sectors in the same mode, but if multiple tracks are present in a CD-ROM, each track can have its sectors in a different mode from the rest of the tracks, they can coexist with audio CD tracks as well, the case of mixed mode CDs. Both Mode 1 and 2 sectors use the first 16 bytes for header information, but differ in the remaining 2,336 bytes due to the use of error correction bytes.
Unlike an audio CD, a CD-ROM cannot rely on error concealment by interpolation. To achieve improved error correction and detection, Mode 1, used for digital data, adds a 32-bit cyclic redundancy check code for error detection, a third layer of Reed–Solomon error correction using a Reed-Solomon Product-like Code. Mode 1 therefore contains 288 bytes per sector for error detection and correction, leaving 2,048 bytes per sector available for data. Mode 2, more appropriate for image or video data, contains no additional error detection or correction bytes, having therefore 2,336 available data bytes per sector. Note that both modes, like audio CDs, still benefit from the lower layers of error correction at the frame level. Before being stored on a disc with the techniques described above, each CD-ROM sector is scrambled to prevent some problematic patterns from showing up; these scrambled sectors follow the same encoding process described in the Red Book in order to be stored
Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio
The gigabyte is a multiple of the unit byte for digital information. The prefix giga means 109 in the International System of Units. Therefore, one gigabyte is 1000000000bytes; the unit symbol for the gigabyte is GB. This definition is used in all contexts of science, engineering and many areas of computing, including hard drive, solid state drive, tape capacities, as well as data transmission speeds. However, the term is used in some fields of computer science and information technology to denote 1073741824 bytes for sizes of RAM; the use of gigabyte may thus be ambiguous. Hard disk capacities as described and marketed by drive manufacturers using the standard metric definition of the gigabyte, but when a 500-GB drive's capacity is displayed by, for example, Microsoft Windows, it is reported as 465 GB, using a binary interpretation. To address this ambiguity, the International System of Quantities standardizes the binary prefixes which denote a series of integer powers of 1024. With these prefixes, a memory module, labeled as having the size 1GB has one gibibyte of storage capacity.
The term gigabyte is used to mean either 10003 bytes or 10243 bytes. The latter binary usage originated as compromise technical jargon for byte multiples that needed to be expressed in a power of 2, but lacked a convenient name; as 1024 is 1000 corresponding to SI multiples, it was used for binary multiples as well. In 1998 the International Electrotechnical Commission published standards for binary prefixes, requiring that the gigabyte denote 10003 bytes and gibibyte denote 10243 bytes. By the end of 2007, the IEC Standard had been adopted by the IEEE, EU, NIST, in 2009 it was incorporated in the International System of Quantities; the term gigabyte continues to be used with the following two different meanings: 1 GB = 1000000000 bytes Based on powers of 10, this definition uses the prefix giga- as defined in the International System of Units. This is the recommended definition by the International Electrotechnical Commission; this definition is used in networking contexts and most storage media hard drives, flash-based storage, DVDs, is consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance.
The file manager of Mac OS X version 10.6 and versions are a notable example of this usage in software, which report files sizes in decimal units. 1 GiB = 1073741824 bytes. The binary definition uses powers of the base 2, as does the architectural principle of binary computers; this usage is promulgated by some operating systems, such as Microsoft Windows in reference to computer memory. This definition is synonymous with the unambiguous unit gibibyte. Since the first disk drive, the IBM 350, disk drive manufacturers expressed hard drive capacities using decimal prefixes. With the advent of gigabyte-range drive capacities, manufacturers based most consumer hard drive capacities in certain size classes expressed in decimal gigabytes, such as "500 GB"; the exact capacity of a given drive model is slightly larger than the class designation. All manufacturers of hard disk drives and flash-memory disk devices continue to define one gigabyte as 1000000000bytes, displayed on the packaging; some operating systems such as OS X express hard drive capacity or file size using decimal multipliers, while others such as Microsoft Windows report size using binary multipliers.
This discrepancy causes confusion, as a disk with an advertised capacity of, for example, 400 GB might be reported by the operating system as 372 GB, meaning 372 GiB. The JEDEC memory standards use IEEE 100 nomenclature; the difference between units based on decimal and binary prefixes increases as a semi-logarithmic function—for example, the decimal kilobyte value is nearly 98% of the kibibyte, a megabyte is under 96% of a mebibyte, a gigabyte is just over 93% of a gibibyte value. This means that a 300 GB hard disk might be indicated variously as 300 GB, 279 GB or 279 GiB, depending on the operating system; as storage sizes increase and larger units are used, these differences become more pronounced. Some legal challenges have been waged over this confusion such as a lawsuit against drive manufacturer Western Digital. Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity. Seagate was sued on similar grounds and settled.
Because of its physical design, the capacity of modern computer random access memory devices, such as DIMM modules, is always a multiple of a power of 1024. It is thus convenient to use prefixes denoting powers of 1024, known as binary prefixes, in describing them. For example, a memory capacity of 1073741824bytes is conveniently expressed as 1 GiB rather than as 1.074 GB. The former specification is, however quoted as "1 GB" when applied to random access memory. Software allocates memory in varying degrees of granularity as needed to fulfill data structure requirements and binary multiples are not required. Other computer capacities and rates, like storage hardware size, data transfer rates, clock speeds, operations per second, etc. do not depend on an inherent base, are presented in decimal units. For example, the manufacturer of a "300 GB" hard drive is claiming a capacity of 300000000000bytes, not 300x10243 bytes. One hour of SDTV video at 2.2 Mbit/s is 1 GB. Seven minutes of HDTV video at 19.39 Mbit/s is 1
A web server is server software, or hardware dedicated to running said software, that can satisfy World Wide Web client requests. A web server can, in general, contain one or more websites. A web server processes incoming network requests over several other related protocols; the primary function of a web server is to store and deliver web pages to clients. The communication between client and server takes place using the Hypertext Transfer Protocol. Pages delivered are most HTML documents, which may include images, style sheets and scripts in addition to the text content. A user agent a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource or an error message if unable to do so; the resource is a real file on the server's secondary storage, but this is not the case and depends on how the web server is implemented. While the primary function is to serve content, a full implementation of HTTP includes ways of receiving content from clients.
This feature is used for submitting web forms, including uploading of files. Many generic web servers support server-side scripting using Active Server Pages, PHP, or other scripting languages; this means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. This function is used to generate HTML documents dynamically as opposed to returning static documents; the former is used for retrieving or modifying information from databases. The latter is much faster and more cached but cannot deliver dynamic content. Web servers can be found embedded in devices such as printers, routers and serving only a local network; the web server may be used as a part of a system for monitoring or administering the device in question. This means that no additional software has to be installed on the client computer since only a web browser is required. In March 1989 Sir Tim Berners-Lee proposed a new project to his employer CERN, with the goal of easing the exchange of information between scientists by using a hypertext system.
The project resulted in Berners-Lee writing two programs in 1990: A Web browser called WorldWideWeb The world's first web server known as CERN httpd, which ran on NeXTSTEPBetween 1991 and 1994, the simplicity and effectiveness of early technologies used to surf and exchange data through the World Wide Web helped to port them to many different operating systems and spread their use among scientific organizations and universities, subsequently to the industry. In 1994 Berners-Lee decided to constitute the World Wide Web Consortium to regulate the further development of the many technologies involved through a standardization process. Web servers are able to map the path component of a Uniform Resource Locator into: A local file system resource An internal or external program name For a static request the URL path specified by the client is relative to the web server's root directory. Consider the following URL as it would be requested by a client over HTTP: http://www.example.com/path/file.html The client's user agent will translate it into a connection to www.example.com with the following HTTP 1.1 request: GET /path/file.html HTTP/1.1 Host: www.example.com The web server on www.example.com will append the given path to the path of its root directory.
On an Apache server, this is /home/www. The result is the local file system resource: /home/www/path/file.html The web server reads the file, if it exists, sends a response to the client's web browser. The response will describe the content of the file and contain the file itself or an error message will return saying that the file does not exist or is unavailable. A web server can be either incorporated in user space. Web servers that run in user-mode have to ask the system for permission to use more memory or more CPU resources. Not only do these requests to the kernel take time, but they are not always satisfied because the system reserves resources for its own usage and has the responsibility to share hardware resources with all the other running applications. Executing in user mode can mean useless buffer copies which are another handicap for user-mode web servers. A web server has defined load limits, because it can handle only a limited number of concurrent client connections per IP address and it can serve only a certain maximum number of requests per second depending on: its own settings, the HTTP request type, whether the content is static or dynamic, whether the content is cached, the hardware and software limitations of the OS of the computer on which the web server runs.
When a web server is near to or over its limit, it becomes unresponsive. At any time web servers can be overloaded due to: Excess legitimate web traffic. Thousands or millions of clients connecting to the web site in a short interval, e.g. Slashdot effect. A denial-of-service attack or distributed denial-of-service attack is an attempt to make a computer or network resource unavailable to its intended users.
The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB; the unit prefix mega is a multiplier of 1000000 in the International System of Units. Therefore, one megabyte is one million bytes of information; this definition has been incorporated into the International System of Quantities. However, in the computer and information technology fields, several other definitions are used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as 1048576bytes, a measurement that conveniently expresses the binary multiples inherent in digital computer memory architectures. However, most standards bodies have deprecated this usage in favor of a set of binary prefixes, in which this quantity is designated by the unit mebibyte. Less common is a convention that used the megabyte to mean 1000×1024 bytes; the megabyte is used to measure either 10002 bytes or 10242 bytes. The interpretation of using base 1024 originated as a compromise technical jargon for the byte multiples that needed to be expressed by the powers of 2 but lacked a convenient name.
As 1024 approximates 1000 corresponding to the SI prefix kilo-, it was a convenient term to denote the binary multiple. In 1998 the International Electrotechnical Commission proposed standards for binary prefixes requiring the use of megabyte to denote 10002 bytes and mebibyte to denote 10242 bytes. By the end of 2009, the IEC Standard had been adopted by the IEEE, EU, ISO and NIST; the term megabyte continues to be used with different meanings: Base 10 1 MB = 1000000 bytes is the definition recommended by the International System of Units and the International Electrotechnical Commission IEC. This definition is used in networking contexts and most storage media hard drives, flash-based storage, DVDs, is consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance; the Mac OS X 10.6 file manager is a notable example of this usage in software. Since Snow Leopard, file sizes are reported in decimal units. In this convention, one thousand megabytes is equal to one gigabyte, where 1 GB is one billion bytes.
Base 2 1 MB = 1048576 bytes is the definition used by Microsoft Windows in reference to computer memory, such as RAM. This definition is synonymous with the unambiguous binary prefix mebibyte. In this convention, one thousand and twenty-four megabytes is equal to one gigabyte, where 1 GB is 10243 bytes. Mixed 1 MB = 1024000 bytes is the definition used to describe the formatted capacity of the 1.44 MB 3.5-inch HD floppy disk, which has a capacity of 1474560bytes. Semiconductor memory doubles in size for each address lane added to an integrated circuit package, which favors counts that are powers of two; the capacity of a disk drive is the product of the sector size, number of sectors per track, number of tracks per side, the number of disk platters in the drive. Changes in any of these factors would not double the size. Sector sizes were set as powers of two for convenience in processing, it was a natural extension to give the capacity of a disk drive in multiples of the sector size, giving a mix of decimal and binary multiples when expressing total disk capacity.
Depending on compression methods and file format, a megabyte of data can be: a 1 megapixel bitmap image with 256 colors stored without any compression. A 4 megapixel JPEG image with normal compression. 1 minute of 128 kbit/s MP3 compressed music. 6 seconds of uncompressed CD audio. A typical English book volume in plain text format; the human genome consists of DNA representing 800 MB of data. The parts that differentiate one person from another can be compressed to 4 MB. Timeline of binary prefixes Gigabyte § Consumer confusion Historical Notes About The Cost Of Hard Drive Storage Space the megabyte International Electrotechnical Commission definitions IEC prefixes and symbols for binary multiples