Microsoft Windows is a group of several graphical operating system families, all of which are developed and sold by Microsoft. Each family caters to a certain sector of the computing industry. Active Windows families include Windows Embedded. Defunct Windows families include Windows Mobile and Windows Phone. Microsoft introduced an operating environment named Windows on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces. Microsoft Windows came to dominate the world's personal computer market with over 90% market share, overtaking Mac OS, introduced in 1984. Apple came to see Windows as an unfair encroachment on their innovation in GUI development as implemented on products such as the Lisa and Macintosh. On PCs, Windows is still the most popular operating system. However, in 2014, Microsoft admitted losing the majority of the overall operating system market to Android, because of the massive growth in sales of Android smartphones.
In 2014, the number of Windows devices sold was less than 25 %. This comparison however may not be relevant, as the two operating systems traditionally target different platforms. Still, numbers for server use of Windows show one third market share, similar to that for end user use; as of October 2018, the most recent version of Windows for PCs, tablets and embedded devices is Windows 10. The most recent versions for server computers is Windows Server 2019. A specialized version of Windows runs on the Xbox One video game console. Microsoft, the developer of Windows, has registered several trademarks, each of which denote a family of Windows operating systems that target a specific sector of the computing industry; as of 2014, the following Windows families are being developed: Windows NT: Started as a family of operating systems with Windows NT 3.1, an operating system for server computers and workstations. It now consists of three operating system subfamilies that are released at the same time and share the same kernel: Windows: The operating system for mainstream personal computers and smartphones.
The latest version is Windows 10. The main competitor of this family is macOS by Apple for personal computers and Android for mobile devices. Windows Server: The operating system for server computers; the latest version is Windows Server 2019. Unlike its client sibling, it has adopted a strong naming scheme; the main competitor of this family is Linux. Windows PE: A lightweight version of its Windows sibling, meant to operate as a live operating system, used for installing Windows on bare-metal computers, recovery or troubleshooting purposes; the latest version is Windows PE 10. Windows IoT: Initially, Microsoft developed Windows CE as a general-purpose operating system for every device, too resource-limited to be called a full-fledged computer. However, Windows CE was renamed Windows Embedded Compact and was folded under Windows Compact trademark which consists of Windows Embedded Industry, Windows Embedded Professional, Windows Embedded Standard, Windows Embedded Handheld and Windows Embedded Automotive.
The following Windows families are no longer being developed: Windows 9x: An operating system that targeted consumers market. Discontinued because of suboptimal performance. Microsoft now caters to the consumer market with Windows NT. Windows Mobile: The predecessor to Windows Phone, it was a mobile phone operating system; the first version was called Pocket PC 2000. The last version is Windows Mobile 6.5. Windows Phone: An operating system sold only to manufacturers of smartphones; the first version was Windows Phone 7, followed by Windows Phone 8, the last version Windows Phone 8.1. It was succeeded by Windows 10 Mobile; the term Windows collectively describes any or all of several generations of Microsoft operating system products. These products are categorized as follows: The history of Windows dates back to 1981, when Microsoft started work on a program called "Interface Manager", it was announced in November 1983 under the name "Windows", but Windows 1.0 was not released until November 1985.
Windows 1.0 was to achieved little popularity. Windows 1.0 is not a complete operating system. The shell of Windows 1.0 is a program known as the MS-DOS Executive. Components included Calculator, Cardfile, Clipboard viewer, Control Panel, Paint, Reversi and Write. Windows 1.0 does not allow overlapping windows. Instead all windows are tiled. Only modal dialog boxes may appear over other windows. Microsoft sold as included Windows Development libraries with the C development environment, which included numerous windows samples. Windows 2.0 was released in December 1987, was more popular than its predecessor. It features several improvements to the user memory management. Windows 2.03 changed the OS from tiled windows to overlapping windows. The result of this change led to Apple Computer filing a suit against Microsoft alleging infringement on Apple's copyrights. Windows 2.0
An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is executed directly by the hardware and makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers; the dominant desktop operating system is Microsoft Windows with a market share of around 82.74%. MacOS by Apple Inc. is in second place, the varieties of Linux are collectively in third place. In the mobile sector, use in 2017 is up to 70% of Google's Android and according to third quarter 2016 data, Android on smartphones is dominant with 87.5 percent and a growth rate 10.3 percent per year, followed by Apple's iOS with 12.1 percent and a per year decrease in market share of 5.2 percent, while other operating systems amount to just 0.3 percent.
Linux distributions are dominant in supercomputing sectors. Other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can only run one program at a time, while a multi-tasking operating system allows more than one program to be running in concurrency; this is achieved by time-sharing, where the available processor time is divided between multiple processes. These processes are each interrupted in time slices by a task-scheduling subsystem of the operating system. Multi-tasking may be characterized in co-operative types. In preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, such as Solaris and Linux—as well as non-Unix-like, such as AmigaOS—support preemptive multitasking. Cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking.
32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem. A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users, the system permits multiple users to interact with the system at the same time. Time-sharing operating systems schedule tasks for efficient use of the system and may include accounting software for cost allocation of processor time, mass storage and other resources to multiple users. A distributed operating system manages a group of distinct computers and makes them appear to be a single computer; the development of networked computers that could be linked and communicate with each other gave rise to distributed computing. Distributed computations are carried out on more than one machine; when computers in a group work in cooperation, they form a distributed system.
In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system saving it as a tool for multiple running virtual machines. The technique is used both in virtualization and cloud computing management, is common in large server warehouses. Embedded operating systems are designed to be used in embedded computer systems, they are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources, they are compact and efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is an operating system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, it uses specialized scheduling algorithms so that a deterministic nature of behavior is achieved. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.
A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with the application and configuration code to construct a unikernel: a specialized, single address space, machine image that can be deployed to cloud or embedded environments. Early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could automatically run different programs in succession to speed up processing. Operating systems did not exist in their more complex forms until the early 1960s. Hardware features were added, that enabled use of runtime libraries and parallel processing; when personal computers became popular in the 1980s, operating systems were made for them similar in concept to those used on larger computers. In the 1940s, the earliest electronic digital systems had no operating systems.
Electronic systems of this time were programmed on rows of mechanical switches or by jumper wires on plug boards. These were special-purpose systems that, for example, generated ballistics tables for the military or controlled the pri
The Invisible Internet Project is an anonymous network layer that allows for censorship-resistant, peer to peer communication. Anonymous connections are achieved by encrypting the user's traffic, sending it through a volunteer-run network of 55,000 computers distributed around the world. Given the high number of possible paths the traffic can transit, a third party watching a full connection is unlikely; the software that implements this layer is called an "I2P router", a computer running I2P is called an "I2P node". I2P is free and open source, is published under multiple licenses. I2P is beta software since 2003; the software's developers emphasize that there are to be bugs in the beta version and that there has been insufficient peer review to date. However, they believe the code is now reasonably stable and well-developed, more exposure can help development of I2P; the network itself is message-based, but there is a library available to allow reliable streaming communication on top of it. All communication is end-to-end encrypted through garlic routing, the end points are cryptographic identifiers, so that neither sender nor recipient of a message need to reveal their IP address to the other side or to third-party observers.
Although many developers had been a part of the Invisible IRC Project and Freenet communities, there are significant differences between their designs and concepts. IIP was an anonymous centralized IRC server. Freenet is a censorship-resistant distributed data store. I2P is an anonymous peer-to-peer distributed communication layer designed to run any traditional internet service, as well as more traditional distributed applications. Many developers of I2P are known only under pseudonyms. While the previous main developer, jrandom, is on hiatus, such as zzz and Complication have continued to lead development efforts, are assisted by numerous contributors. I2P uses 2048bit ElGamal/AES256/SHA256+Session Tags encryption and Ed25519 EdDSA/ECDSA signatures. I2P has had a stable release every six to eight weeks. Updates are signed by the release manager. Since I2P is an anonymous network layer, it is designed so other software can use it for anonymous communication; as such, there are a variety of tools available for I2P or in development.
The I2P router is controlled through the router console, a web frontend accessed through a web browser. I2PTunnel is an application embedded into I2P that allows arbitrary TCP/IP applications to communicate over I2P by setting up "tunnels" which can be accessed by connecting to pre-determined ports on localhost. SAM is a protocol which allows a client application written in any programming language to communicate over I2P, by using a socket-based interface to the I2P router. BOB is a less complex app to router protocol similar to "SAM" Orchid Outproxy Tor plugin Any IRC client made for the Internet Relay Chat can work, once connected to the I2P IRC server. Several programs provide BitTorrent functionality for use within the I2P network. Users cannot connect to non-I2P torrents or peers from within I2P, nor can they connect to I2P torrents or peers from outside I2P. I2PSnark, included in the I2P install package, is a port of the BitTorrent client named Snark. Vuze known as Azureus, is a BitTorrent client that includes a plugin for I2P, allowing anonymous swarming through this network.
This plugin is still in an early stage of development, however it is fairly stable. I2P-BT is a BitTorrent client for I2P; this client is a modified version of the original BitTorrent 3.4.2 program which runs on MS Windows and most dialects of Unix in a GUI and command-line environment. It was developed by the individual known as'duck' on I2P in cooperation with'smeghead', it is no longer being developed. I2PRufus is an I2P port of the Rufus BitTorrent client. Robert is the most maintained I2PRufus fork. XD is a standalone BitTorrent client written in Go. Two Kad network clients exist for iMule and Nachtblitz. IMule is a port of eMule for I2P network. IMule has not been developed since 2013. IMule is made for anonymous file sharing. In contrast to other eDonkey clients, iMule only uses the Kademlia for proceeding to connect through I2P network, so no servers are needed. Nachtblitz is a custom client built on the. NET Framework; the latest version is 1.4.27, released on March 23, 2016. Nachtblitz includes.
I2Phex is a port of the popular Gnutella client Phex to I2P. It is stable and functional. A port of Tahoe-LAFS has been ported to I2P; this allows for files to be anonymously stored in Tahoe-LAFS grids. Vuze is the only torrent client that make clearnet torrents available on I2P and vice versa, by using a plugin that connects them to the I2P network. Depending on the client settings, torrents from the internet can be made available on I2P and torrents from I2P can be made available to the intern
Facebook, Inc. is an American online social media and social networking service company. It is based in California, it was founded by Mark Zuckerberg, along with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dustin Moskovitz and Chris Hughes. It is considered one of the Big Four technology companies along with Amazon and Google; the founders limited the website's membership to Harvard students and subsequently Columbia and Yale students. Membership was expanded to the remaining Ivy League schools, MIT, higher education institutions in the Boston area. Facebook added support for students at various other universities, to high school students. Since 2006, anyone who claims to be at least 13 years old has been allowed to become a registered user of Facebook, though variations exist in this requirement, depending on local laws; the name comes from the face book directories given to American university students. Facebook held its initial public offering in February 2012, valuing the company at $104 billion, the largest valuation to date for a newly listed public company.
It began selling stock to the public three months later. Facebook makes most of its revenue from advertisements; the Facebook service can be accessed from devices with Internet connectivity, such as personal computers and smartphones. After registering, users can create a customized profile revealing information about themselves. Users can post text and multimedia of their own devising and share it with other users as "friends". Users can use various embedded apps, receive notifications of their friends' activities. Users may join common-interest groups. Facebook had more than 2.3 billion monthly active users as of December 2018. It receives prominent media coverage, including many controversies such as user privacy and psychological effects; the company has faced intense pressure over censorship and over content that some users find objectionable. Facebook offers other services, it independently developed Facebook Messenger. Zuckerberg built; the site was comparable to Hot or Not and used "photos compiled from the online facebooks of nine Houses, placing two next to each other at a time and asking users to choose the "hotter" person".
Facemash attracted 22,000 photo-views in its first four hours. The site was sent to several campus group list-servers, but was shut down a few days by Harvard administration. Zuckerberg faced expulsion and was charged with breaching security, violating copyrights and violating individual privacy; the charges were dropped. Zuckerberg expanded on this project that semester by creating a social study tool ahead of an art history final exam, he uploaded all art images to a website, each of, accompanied by a comments section shared the site with his classmates. A "face book" is a student directory featuring personal information. In 2003, Harvard had only a paper version along with private online directories. Zuckerberg told the Crimson, "Everyone's been talking a lot about a universal face book within Harvard.... I think. I can do it better than they can, I can do it in a week." In January 2004, Zuckerberg coded a new website, known as "TheFacebook", inspired by a Crimson editorial about Facemash, stating, "It is clear that the technology needed to create a centralized Website is available... the benefits are many."
Zuckerberg met with Harvard student Eduardo Saverin, each of them agreed to invest $1,000 in the site. On February 4, 2004, Zuckerberg launched "TheFacebook" located at thefacebook.com. Six days after the site launched, Harvard seniors Cameron Winklevoss, Tyler Winklevoss, Divya Narendra accused Zuckerberg of intentionally misleading them into believing that he would help them build a social network called HarvardConnection.com. They claimed; the three complained to the Crimson and the newspaper began an investigation. They sued Zuckerberg, settling in 2008 for 1.2 million shares. Membership was restricted to students of Harvard College. Within a month, more than half the undergraduates had registered. Dustin Moskovitz, Andrew McCollum, Chris Hughes joined Zuckerberg to help manage the growth of the website. In March 2004, Facebook expanded to Columbia and Yale. and to all Ivy League colleges, Boston University, New York University, MIT, Washington and successively most universities in the United States and Canada.
In mid-2004, Napster co-founder and entrepreneur Sean Parker—an informal advisor to Zuckerberg—became company president. In June 2004, the company moved to California, it received its first investment that month from PayPal co-founder Peter Thiel. In 2005, the company dropped "the" from its name after purchasing the domain name facebook.com for US$200,000. The domain had belonged to AboutFace Corporation. In May 2005, Accel Partners invested $12.7 million in Facebook, Jim Breyer added $1 million of his own money. A high-school version of the site launched in September 2005. Eligibility expanded to include employees including Apple Inc. and Microsoft. On September 26, 2006, Facebook opened to everyone at least 13 years old with a valid email address. By late 2007, Facebook had 100,000 pages. Organization pages began rolling out in May 2009. On October 24, 2007, Microsoft announced th
Gtk-gnutella is a peer-to-peer file sharing application which runs on the gnutella network. Gtk-gnutella uses the GTK+ toolkit for its graphical user interface. Released under the GNU General Public License, gtk-gnutella is free software. Gtk-gnutella was written to look like the original Nullsoft Gnutella client; the original author Yann Grossel stopped working on the client in early 2001. After a while Raphael Manfredi took over as the main software architect, the client has been in active development since. Versions released after July 2002 do not look like the original Nullsoft client. Gtk-gnutella is programmed in C with an emphasis on efficiency and portability without being minimalistic but rather head-on with most of the modern features of the gnutella network. Therefore, it requires fewer resources than the major gnutella clients, it can be used as headless gnutella client not requiring GTK+ at all. Gtk-gnutella has a filtering engine. Gtk-gnutella supports a large range of the features of modern gnutella clients.
Gtk-gnutella was the first gnutella client to support IPv6 and encryption using TLS. It can export magnet links, it has strong internationalization features, supporting English, Greek, Hungarian, Japanese, Norwegian and Chinese. Gtk-gnutella has support to prevent spamming and other hostile peer activity. Several software distributions provide pre-compiled packages, but they are outdated as many distributions version freeze old stable releases; the gnutella network benefits from running the latest version obtainable as peer and hostile IP address lists change making building the latest SVN snapshot the best option. There are pre-compiled packages for many Linux distributions available online. Persons concerned about security might wish to compile their own; the gtk-gnutella sources use configuration system instead of Autoconf. Most users are only familiar with the configure scripts generated by the latter. Another hazard for novices is configuring NAT devices to enable full network connectivity for gtk-gnutella.
Gtk-gnutella, like any gnutella client, is still usable behind a firewall or a router, but with some reduced functionality, if it cannot receive incoming TCP connections or UDP packets. In an attempt to mitigate the issue for newcomers, gtk-gnutalla implements the UPnP and NAT-PMP client protocols. Gtk-gnutella supports features for downloading larger files. Version 0.96.4 supports Tiger tree hash serving and versions after 0.96.5 support tiger tree hashes for uploads and downloads. Tiger tree hashing and other gtk-gnutella features make file transfers as efficient as BitTorrent. Gtk-gnutella supports partial file sharing, remote queueing and files larger than 4 GiB. Overlap checking was the only mechanism to guard against bad data prior to versions 0.96.4. Overlap checking does not guard against malicious corruption. Version 0.96.6 introduced preliminary support for a Kademlia DHT, completed in version 0.96.7. The DHT is replacing search by SHA-1, when locating alternate sources for a known file or looking for push-proxies.
In version 0.96.7, the DHT is enabled by default. LimeWire first developed the DHT and named it Mojito DHT. Version 0.96.9 introduced full native support for UPnP and NAT-PMP, making the usage behind a compatible router much easier since there is no longer any need to manually forward ports on the firewall. In this version the code was ported to Microsoft Windows however the Windows port is still considered beta due to lack of wide testing so far. Version 0.96.9 introduced important DHT protection against Sybil attacks, using algorithms based on statistical properties. Version 0.97 was a major release, introducing client-side support for HTTP pipelining, "What's New?" queries, MIME type query filtering, GUESS support and partial file querying. Although many Gnutella vendors supported server-side GUESS, gtk-gnutella introduced the client-side as well enhancing the original specifications of the protocol to make it usable. Version 0.98.2 employs a minor patch to correct malloc memory allocations and multiple threads issues on Ubuntu 11.10 operating systems.
This 2011 gtk-gnutella version was dedicated to the memory of Dennis Ritchie, 1941-2011. Version 0.98.4 added improved partial file transfers. Version 1.1 is a major release which added G2 support: gtk-gnutella will now connect to the G2 network in leaf mode. This lets local queries be propagated to the G2 network as well. File exchanges with G2 hosts are inter-operable and are permitted without restriction. Gtk-gnutella does not rank. Gtk-gnutella developers' proposals have been incorporated into many gnutella clients. In 2011, gtk-gnutella vendor extensions are the third most prolific on the GDF, following Limewire and Bearshare. Salon listed gtk-gnutella as one of the five most popular gnutella applications in 2002. XoloX and Toadnode in the list, are no longer developed. Gtk-gnutella homepage #gtk-gnutella connect on freenode
United States dollar
The United States dollar is the official currency of the United States and its territories per the United States Constitution since 1792. In practice, the dollar is divided into 100 smaller cent units, but is divided into 1000 mills for accounting; the circulating paper money consists of Federal Reserve Notes that are denominated in United States dollars. Since the suspension in 1971 of convertibility of paper U. S. currency into any precious metal, the U. S. dollar is, de facto, fiat money. As it is the most used in international transactions, the U. S. dollar is the world's primary reserve currency. Several countries use it as their official currency, in many others it is the de facto currency. Besides the United States, it is used as the sole currency in two British Overseas Territories in the Caribbean: the British Virgin Islands and Turks and Caicos Islands. A few countries use the Federal Reserve Notes for paper money, while still minting their own coins, or accept U. S. dollar coins. As of June 27, 2018, there are $1.67 trillion in circulation, of which $1.62 trillion is in Federal Reserve notes.
Article I, Section 8 of the U. S. Constitution provides that the Congress has the power "To coin money". Laws implementing this power are codified at 31 U. S. C. § 5112. Section 5112 prescribes the forms; these coins are both designated in Section 5112 as "legal tender" in payment of debts. The Sacagawea dollar is one example of the copper alloy dollar; the pure silver dollar is known as the American Silver Eagle. Section 5112 provides for the minting and issuance of other coins, which have values ranging from one cent to 100 dollars; these other coins are more described in Coins of the United States dollar. The Constitution provides that "a regular Statement and Account of the Receipts and Expenditures of all public Money shall be published from time to time"; that provision of the Constitution is made specific by Section 331 of Title 31 of the United States Code. The sums of money reported in the "Statements" are being expressed in U. S. dollars. The U. S. dollar may therefore be described as the unit of account of the United States.
The word "dollar" is one of the words in the first paragraph of Section 9 of Article I of the Constitution. There, "dollars" is a reference to the Spanish milled dollar, a coin that had a monetary value of 8 Spanish units of currency, or reales. In 1792 the U. S. Congress passed a Coinage Act. Section 9 of that act authorized the production of various coins, including "DOLLARS OR UNITS—each to be of the value of a Spanish milled dollar as the same is now current, to contain three hundred and seventy-one grains and four sixteenth parts of a grain of pure, or four hundred and sixteen grains of standard silver". Section 20 of the act provided, "That the money of account of the United States shall be expressed in dollars, or units... and that all accounts in the public offices and all proceedings in the courts of the United States shall be kept and had in conformity to this regulation". In other words, this act designated the United States dollar as the unit of currency of the United States. Unlike the Spanish milled dollar, the U.
S. dollar is based upon a decimal system of values. In addition to the dollar the coinage act established monetary units of mill or one-thousandth of a dollar, cent or one-hundredth of a dollar, dime or one-tenth of a dollar, eagle or ten dollars, with prescribed weights and composition of gold, silver, or copper for each, it was proposed in the mid-1800s that one hundred dollars be known as a union, but no union coins were struck and only patterns for the $50 half union exist. However, only cents are in everyday use as divisions of the dollar. XX9 per gallon, e.g. $3.599, more written as $3.599⁄10. When issued in circulating form, denominations equal to or less than a dollar are emitted as U. S. coins while denominations equal to or greater than a dollar are emitted as Federal Reserve notes. Both one-dollar coins and notes are produced today, although the note form is more common. In the past, "paper money" was issued in denominations less than a dollar and gold coins were issued for circulation up to the value of $20.
The term eagle was used in the Coinage Act of 1792 for the denomination of ten dollars, subsequently was used in naming gold coins. Paper currency less than one dollar in denomination, known as "fractional currency", was sometimes pejoratively referred to as "shinplasters". In 1854, James Guthrie Secretary of the Treasury, proposed creating $100, $50 and $25 gold coins, which were referred to as a "Union", "Half Union", "Quarter Union", thus implying a denomination of 1 Union = $100. Today, USD notes are made from cotton fiber paper, unlike most common paper, made of wood fiber. U. S. coins are produced by the United States Mint. U. S. dollar banknotes are printed by the Bureau of Engraving and Printing and, since 1914, have been issued by t
Windows Media Audio
Windows Media Audio is a series of audio codecs and their corresponding audio coding formats developed by Microsoft. It is a proprietary technology. WMA consists of four distinct codecs; the original WMA codec, known as WMA, was conceived as a competitor to the popular MP3 and RealAudio codecs. WMA Pro, a newer and more advanced codec, supports high resolution audio. A lossless codec, WMA Lossless, compresses audio data without loss of audio fidelity. WMA Voice, targeted at voice content, applies compression using a range of low bit rates. Microsoft has developed a digital container format called Advanced Systems Format to store audio encoded by WMA; the first WMA codec was based on earlier work by Henrique Malvar and his team, transferred to the Windows Media team at Microsoft. Malvar was a senior researcher and manager of the Signal Processing Group at Microsoft Research, whose team worked on the MSAudio project; the first finalized codec was referred to as MSAudio 4.0. It was officially released as Windows Media Audio, as part of Windows Media Technologies 4.0.
Microsoft claimed that WMA could produce files that were half the size of equivalent-quality MP3 files. The former claim however was rejected by some audiophiles. RealNetworks challenged Microsoft's claims regarding WMA's superior audio quality compared to RealAudio. Newer versions of WMA became available: Windows Media Audio 2 in 1999, Windows Media Audio 7 in 2000, Windows Media Audio 8 in 2001, Windows Media Audio 9 in 2003. Microsoft first announced its plans to license WMA technology to third parties in 1999. Although earlier versions of Windows Media Player played WMA files, support for WMA file creation was not added until the seventh version. In 2003, Microsoft released new audio codecs; these codecs were Windows Media Audio 9 Professional, Windows Media Audio 9 Lossless, Windows Media Audio 9 Voice. All versions of WMA released since version 9.0 - namely 9.1, 9.2 and 10 - have been backwards compatible with the original v9 decoder and are therefore not considered separate codecs. The sole exception to this is the WMA 10 Professional codec whose Low Bit Rate mode is only backwards compatible with the older WMA Professional decoders at half sampling rate.
Full fidelity decoding of WMA 10 Professional LBR bitstreams requires a WMA version 10 or newer decoder. A WMA file is in most circumstances contained in the Advanced Systems Format, a proprietary Microsoft container format for digital audio or digital video; the ASF container format specifies how metadata about the file is to be encoded, similar to the ID3 tags used by MP3 files. Metadata may include song name, track number, artist name, audio normalization values; this container can optionally support digital rights management using a combination of elliptic curve cryptography key exchange, DES block cipher, a custom block cipher, RC4 stream cipher and the SHA-1 hashing function. See Windows Media DRM for further information. Since 2008 Microsoft has been using WMA Professional in its Protected Interoperable File Format based on the ISO Base Media File Format and most used for Smooth Streaming, a form of adaptive bit rate streaming over HTTP. Related industry standards such as DECE UltraViolet and MPEG-DASH have not standardized WMA as a supported audio codec, deciding in favor of the more industry-prevalent MPEG and Dolby audio codecs.
Each WMA file features a single audio track in one of the four sub-formats: WMA, WMA Pro, WMA Lossless, or WMA Voice. These formats use different codes that are mutually incompatible; each codec is further explained below. Windows Media Audio is the most common codec of the four WMA codecs. Colloquial usage of the term WMA in marketing materials and device specifications refers to this codec only; the first version of the codec released in 1999 is regarded as WMA 1. In the same year, the bit stream syntax, or compression algorithm, was altered in minor ways and became WMA 2. Since newer versions of the codec have been released, but the decoding process remained the same, ensuring compatibility between codec versions. WMA is a lossy audio codec based on the study of psychoacoustics. Audio signals that are deemed to be imperceptible to the human ear are encoded with reduced resolution during the compression process. WMA can encode audio signals sampled at up to 48 kHz with up to two discrete channels.
WMA 9 introduced variable bit rate and average bit rate coding techniques into the MS encoder although both were technically supported by the original format. WMA 9.1 added support for low-delay audio, which reduces latency for encoding and decoding. Fundamentally, WMA is a transform coder based on modified discrete cosine transform, somewhat similar to AAC, Cook and Vorbis; the bit stream of WMA is composed of each containing 1 or more frames of 2048 samples. If the bit reservoir is not used, a frame is equal to a superframe; each frame contains a number of blocks, which are 128, 256, 512, 1024, or 2048 samples long after being transformed into the frequency domain via the MDCT. In the frequency domain, masking for the transformed samples is determined, used to requantize the samples; the floating point samples are decomposed into coefficient and exponent parts and independently huffman coded. Stereo information is mid/side coded. At low bit rates, line spectral pairs and a form of noise codin