Open-source software is a type of computer software in which source code is released under a license in which the copyright holder grants users the rights to study and distribute the software to anyone and for any purpose. Open-source software may be developed in a collaborative public manner. Open-source software is a prominent example of open collaboration. Open-source software development generates an more diverse scope of design perspective than any company is capable of developing and sustaining long term. A 2008 report by the Standish Group stated that adoption of open-source software models have resulted in savings of about $60 billion per year for consumers. In the early days of computing and developers shared software in order to learn from each other and evolve the field of computing; the open-source notion moved to the way side of commercialization of software in the years 1970-1980. However, academics still developed software collaboratively. For example Donald Knuth in 1979 with the TeX typesetting system or Richard Stallman in 1983 with the GNU operating system.
In 1997, Eric Raymond published The Cathedral and the Bazaar, a reflective analysis of the hacker community and free-software principles. The paper received significant attention in early 1998, was one factor in motivating Netscape Communications Corporation to release their popular Netscape Communicator Internet suite as free software; this source code subsequently became the basis behind SeaMonkey, Mozilla Firefox and KompoZer. Netscape's act prompted Raymond and others to look into how to bring the Free Software Foundation's free software ideas and perceived benefits to the commercial software industry, they concluded that FSF's social activism was not appealing to companies like Netscape, looked for a way to rebrand the free software movement to emphasize the business potential of sharing and collaborating on software source code. The new term they chose was "open source", soon adopted by Bruce Perens, publisher Tim O'Reilly, Linus Torvalds, others; the Open Source Initiative was founded in February 1998 to encourage use of the new term and evangelize open-source principles.
While the Open Source Initiative sought to encourage the use of the new term and evangelize the principles it adhered to, commercial software vendors found themselves threatened by the concept of distributed software and universal access to an application's source code. A Microsoft executive publicly stated in 2001 that "open source is an intellectual property destroyer. I can't imagine something that could be worse than this for the software business and the intellectual-property business." However, while Free and open-source software has played a role outside of the mainstream of private software development, companies as large as Microsoft have begun to develop official open-source presences on the Internet. IBM, Oracle and State Farm are just a few of the companies with a serious public stake in today's competitive open-source market. There has been a significant shift in the corporate philosophy concerning the development of FOSS; the free-software movement was launched in 1983. In 1998, a group of individuals advocated that the term free software should be replaced by open-source software as an expression, less ambiguous and more comfortable for the corporate world.
Software licenses grant rights to users which would otherwise be reserved by copyright law to the copyright holder. Several open-source software licenses have qualified within the boundaries of the Open Source Definition; the most prominent and popular example is the GNU General Public License, which "allows free distribution under the condition that further developments and applications are put under the same licence", thus free. The open source label came out of a strategy session held on April 7, 1998 in Palo Alto in reaction to Netscape's January 1998 announcement of a source code release for Navigator. A group of individuals at the session included Tim O'Reilly, Linus Torvalds, Tom Paquin, Jamie Zawinski, Larry Wall, Brian Behlendorf, Sameer Parekh, Eric Allman, Greg Olson, Paul Vixie, John Ousterhout, Guido van Rossum, Philip Zimmermann, John Gilmore and Eric S. Raymond, they used the opportunity before the release of Navigator's source code to clarify a potential confusion caused by the ambiguity of the word "free" in English.
Many people claimed that the birth of the Internet, since 1969, started the open-source movement, while others do not distinguish between open-source and free software movements. The Free Software Foun
Streaming media is multimedia, received by and presented to an end-user while being delivered by a provider. The verb "to stream" refers to the process of obtaining media in this manner. A client end-user can use their media player to start playing digital video or digital audio content before the entire file has been transmitted. Distinguishing delivery method from the media distributed applies to telecommunications networks, as most of the delivery systems are either inherently streaming or inherently non-streaming. For example, in the 1930s, elevator music was among the earliest popular music available as streaming media; the term "streaming media" can apply to media other than video and audio, such as live closed captioning, ticker tape, real-time text, which are all considered "streaming text". Live streaming is the delivery of Internet content in real-time much as live television broadcasts content over the airwaves via a television signal. Live internet streaming requires a form of source media, an encoder to digitize the content, a media publisher, a content delivery network to distribute and deliver the content.
Live streaming does not need to be recorded at the origination point, although it is. There are challenges with streaming content on the Internet. If the user does not have enough bandwidth in their Internet connection, they may experience stops, lags, or slow buffering of the content; some users may not be able to stream certain content due to not having compatible computer or software systems. Some popular streaming services include the video sharing website YouTube and Mixer, which live stream the playing of video games. Netflix and Amazon Video stream movies and TV shows, Spotify, Apple Music and TIDAL stream music. In the early 1920s, George O. Squier was granted patents for a system for the transmission and distribution of signals over electrical lines, the technical basis for what became Muzak, a technology streaming continuous music to commercial customers without the use of radio. Attempts to display media on computers date back to the earliest days of computing in the mid-20th century.
However, little progress was made for several decades due to the high cost and limited capabilities of computer hardware. From the late 1980s through the 1990s, consumer-grade personal computers became powerful enough to display various media; the primary technical issues related to streaming were having enough CPU power bus bandwidth to support the required data rates, creating low-latency interrupt paths in the operating system to prevent buffer underrun, enabling skip-free streaming of the content. However, computer networks were still limited in the mid-1990s, audio and video media were delivered over non-streaming channels, such as by downloading a digital file from a remote server and saving it to a local drive on the end user's computer or storing it as a digital file and playing it back from CD-ROMs. In 1991 the first commercial Ethernet Switch was introduced, which enabled more powerful computer networks leading to the first streaming video solutions used by schools and corporations such as expanding Bloomberg Television worldwide.
In the mid 1990s the World Wide Web was established, but streaming audio would not be practical until years later. During the late 1990s and early 2000s, users had increased access to computer networks the Internet. During the early 2000s, users had access to increased network bandwidth in the "last mile"; these technological improvements facilitated the streaming of audio and video content to computer users in their homes and workplaces. There was an increasing use of standard protocols and formats, such as TCP/IP, HTTP, HTML as the Internet became commercialized, which led to an infusion of investment into the sector; the band Severe Tire Damage was the first group to perform live on the Internet. On June 24, 1993, the band was playing a gig at Xerox PARC while elsewhere in the building, scientists were discussing new technology for broadcasting on the Internet using multicasting; as proof of PARC's technology, the band's performance was broadcast and could be seen live in Australia and elsewhere.
In a March 2017 interview, band member Russ Haines stated that the band had used "half of the total bandwidth of the internet" to stream the performance, a 152-by-76 pixel video, updated eight to twelve times per second, with audio quality, "at best, a bad telephone connection". Microsoft Research developed a Microsoft TV application, compiled under MS Windows Studio Suite and tested in conjunction with Connectix QuickCam. RealNetworks was a pioneer in the streaming media markets, when it broadcast a baseball game between the New York Yankees and the Seattle Mariners over the Internet in 1995; the first symphonic concert on the Internet took place at the Paramount Theater in Seattle, Washington on November 10, 1995. The concert was a collaboration between The Seattle Symphony and various guest musicians such as Slash, Matt Cameron, Barrett Martin; when Word Magazine launched in 1995, they featured the first-ever streaming soundtracks on the Internet. Metro
In computing, floating-point arithmetic is arithmetic using formulaic representation of real numbers as an approximation so as to support a trade-off between range and precision. For this reason, floating-point computation is found in systems which include small and large real numbers, which require fast processing times. A number is, in general, represented to a fixed number of significant digits and scaled using an exponent in some fixed base. A number that can be represented is of the following form: significand × base exponent, where significand is an integer, base is an integer greater than or equal to two, exponent is an integer. For example: 1.2345 = 12345 ⏟ significand × 10 ⏟ base − 4 ⏞ exponent. The term floating point refers to the fact that a number's radix point can "float"; this position is indicated as the exponent component, thus the floating-point representation can be thought of as a kind of scientific notation. A floating-point system can be used to represent, with a fixed number of digits, numbers of different orders of magnitude: e.g. the distance between galaxies or the diameter of an atomic nucleus can be expressed with the same unit of length.
The result of this dynamic range is that the numbers that can be represented are not uniformly spaced. Over the years, a variety of floating-point representations have been used in computers. In 1985, the IEEE 754 Standard for Floating-Point Arithmetic was established, since the 1990s, the most encountered representations are those defined by the IEEE; the speed of floating-point operations measured in terms of FLOPS, is an important characteristic of a computer system for applications that involve intensive mathematical calculations. A floating-point unit is a part of a computer system specially designed to carry out operations on floating-point numbers. A number representation specifies some way of encoding a number as a string of digits. There are several mechanisms. In common mathematical notation, the digit string can be of any length, the location of the radix point is indicated by placing an explicit "point" character there. If the radix point is not specified the string implicitly represents an integer and the unstated radix point would be off the right-hand end of the string, next to the least significant digit.
In fixed-point systems, a position in the string is specified for the radix point. So a fixed-point scheme might be to use a string of 8 decimal digits with the decimal point in the middle, whereby "00012345" would represent 0001.2345. In scientific notation, the given number is scaled by a power of 10, so that it lies within a certain range—typically between 1 and 10, with the radix point appearing after the first digit; the scaling factor, as a power of ten, is indicated separately at the end of the number. For example, the orbital period of Jupiter's moon Io is 152,853.5047 seconds, a value that would be represented in standard-form scientific notation as 1.528535047×105 seconds. Floating-point representation is similar in concept to scientific notation. Logically, a floating-point number consists of: A signed digit string of a given length in a given base; this digit string is referred to mantissa, or coefficient. The length of the significand determines the precision; the radix point position is assumed always to be somewhere within the significand—often just after or just before the most significant digit, or to the right of the rightmost digit.
This article follows the convention that the radix point is set just after the most significant digit. A signed integer exponent. To derive the value of the floating-point number, the significand is multiplied by the base raised to the power of the exponent, equivalent to shifting the radix point from its implied position by a number of places equal to the value of the exponent—to the right if the exponent is positive or to the left if the exponent is negative. Using base-10 as an example, the number 152,853.5047, which has ten decimal digits of precision, is represented as the significand 1,528,535,047 together with 5 as the exponent. To determine the actual value, a decimal point is placed after the first digit of the significand and the result is multiplied by 105 to give 1.528535047×105, or 152,853.5047. In storing such a number, the base need not be stored, since it will be the same for the entire range of supported numbers, can thus be inferred. Symbolically, this final value is: s b p − 1 × b e, where s is the
A podcast or generically netcast, is an episodic series of digital audio or video files which a user can download in order to listen to. It is available for subscription, so that new episodes are automatically downloaded via web syndication to the user's own local computer, mobile application, or portable media player; the word was suggested by Ben Hammersley as a portmanteau of "iPod" and "broadcast". The files distributed are in audio format, but may sometimes include other file formats such as PDF or EPUB. Videos which are shared following a podcast model are sometimes called video vodcasts; the generator of a podcast maintains a central list of the files on a server as a web feed that can be accessed through the Internet. The listener or viewer uses special client application software on a computer or media player, known as a podcatcher, which accesses this web feed, checks it for updates, downloads any new files in the series; this process can be automated to download new files automatically, which may seem to users as though new episodes are broadcast or "pushed" to them.
Files are stored locally on the user's device, ready for offline use. There are many different mobile applications available for people to use to subscribe and to listen to podcasts. Many of these applications allow users to download podcasts or to stream them on demand as an alternative to downloading. Many podcast players allow listeners to control the playback speed; some have labeled podcasting as a converged medium bringing together audio, the web, portable media players, as well as a disruptive technology that has caused some individuals in the radio business to reconsider established practices and preconceptions about audiences, consumption and distribution. Podcasts are free of charge to listeners and can be created for little to no cost, which sets them apart from the traditional model of "gate-kept" media and production tools. Podcast creators can monetize their podcasts by allowing companies to purchase ad time, as well as via sites such as Patreon, which provides special extras and content to listeners for a fee.
Podcasting is much a horizontal media form – producers are consumers, consumers may become producers, both can engage in conversations with each other. "Podcast" is a portmanteau word, formed by combining "iPod" and "broadcast". The term "podcasting" as a name for the nascent technology was first suggested by The Guardian columnist and BBC journalist Ben Hammersley, who invented it in early February 2004 while "padding out" an article for The Guardian newspaper. Despite the etymology, the content can be accessed using any computer or similar device that can play media files. Use of the term "podcast" predated Apple's addition of formal support for podcasting to the iPod, or its iTunes software. Other names for podcasting include "net cast", intended as a vendor-neutral term without the loose reference to the Apple iPod; this name is used by shows from the TWiT.tv network. Some sources have suggested the backronym "portable on demand" or "POD", for similar reasons. In 2004, former MTV video jockey Adam Curry, in collaboration with Dave Winer – co-author of the RSS specification – is credited with coming up with the idea to automate the delivery and syncing of textual content to portable audio players.
Podcasting, once an obscure method of spreading audio information, has become a recognized medium for distributing audio content, whether for corporate or personal use. Podcasts are similar to radio programs in form, but they exist as audio files that can be played at a listener's convenience, anytime or anywhere; the first application to make this process feasible was iPodderX, developed by August Trometer and Ray Slakinski. By 2007, audio podcasts were doing what was accomplished via radio broadcasts, the source of radio talk shows and news programs since the 1930s; this shift occurred as a result of the evolution of internet capabilities along with increased consumer access to cheaper hardware and software for audio recording and editing. In October 2003, Matt Schichter launched. B. B. King, Third Eye Blind, Gavin DeGraw, The Beach Boys, Jason Mraz were notable guests the first season; the hour long radio show was recorded live, transcoded to 16kbit/s audio for dial-up online streaming. Despite a lack of a accepted identifying name for the medium at the time of its creation, The Backstage Pass which became known as Matt Schichter Interviews is believed to be the first podcast to be published online.
In August 2004, Adam Curry launched his show Daily Source Code. It was a show focused on chronicling his everyday life, delivering news, discussions about the development of podcasting, as well as promoting new and emerging podcasts. Curry published it in an attempt to gain traction in the development of what would come to be known as podcasting and as a means of testing the software outside of a lab setting; the name Daily Source Code was chosen in the hope that it would attract an audience with an interest in technology. Daily Source Code started at a grassroots level of production and was directed at podcast developers; as its audience became interested in the format, these developers were inspired to create and produce their own projects and, as a result, they improved the code used to create podcasts. As more people learned how easy it was to produce podcasts, a community of pioneer podcasters appeared. In June 2005, Apple released iTunes 4.9 which added formal support for podcasts, thus negating the need to use a separate program in order to download and transfer them to a mobile device.
While this made access to podcasts more
Central processing unit
A central processing unit called a central processor or main processor, is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic and input/output operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s. Traditionally, the term "CPU" refers to a processor, more to its processing unit and control unit, distinguishing these core elements of a computer from external components such as main memory and I/O circuitry; the form and implementation of CPUs have changed over the course of their history, but their fundamental operation remains unchanged. Principal components of a CPU include the arithmetic logic unit that performs arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations and a control unit that orchestrates the fetching and execution of instructions by directing the coordinated operations of the ALU, registers and other components.
Most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit chip. An IC that contains a CPU may contain memory, peripheral interfaces, other components of a computer; some computers employ a multi-core processor, a single chip containing two or more CPUs called "cores". Array processors or vector processors have multiple processors that operate in parallel, with no unit considered central. There exists the concept of virtual CPUs which are an abstraction of dynamical aggregated computational resources. Early computers such as the ENIAC had to be physically rewired to perform different tasks, which caused these machines to be called "fixed-program computers". Since the term "CPU" is defined as a device for software execution, the earliest devices that could rightly be called CPUs came with the advent of the stored-program computer; the idea of a stored-program computer had been present in the design of J. Presper Eckert and John William Mauchly's ENIAC, but was omitted so that it could be finished sooner.
On June 30, 1945, before ENIAC was made, mathematician John von Neumann distributed the paper entitled First Draft of a Report on the EDVAC. It was the outline of a stored-program computer that would be completed in August 1949. EDVAC was designed to perform a certain number of instructions of various types; the programs written for EDVAC were to be stored in high-speed computer memory rather than specified by the physical wiring of the computer. This overcame a severe limitation of ENIAC, the considerable time and effort required to reconfigure the computer to perform a new task. With von Neumann's design, the program that EDVAC ran could be changed by changing the contents of the memory. EDVAC, was not the first stored-program computer. Early CPUs were custom designs used as part of a sometimes distinctive computer. However, this method of designing custom CPUs for a particular application has given way to the development of multi-purpose processors produced in large quantities; this standardization began in the era of discrete transistor mainframes and minicomputers and has accelerated with the popularization of the integrated circuit.
The IC has allowed complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in electronic devices ranging from automobiles to cellphones, sometimes in toys. While von Neumann is most credited with the design of the stored-program computer because of his design of EDVAC, the design became known as the von Neumann architecture, others before him, such as Konrad Zuse, had suggested and implemented similar ideas; the so-called Harvard architecture of the Harvard Mark I, completed before EDVAC used a stored-program design using punched paper tape rather than electronic memory. The key difference between the von Neumann and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both.
Most modern CPUs are von Neumann in design, but CPUs with the Harvard architecture are seen as well in embedded applications. Relays and vacuum tubes were used as switching elements; the overall speed of a system is dependent on the speed of the switches. Tube computers like EDVAC tended to average eight hours between failures, whereas relay computers like the Harvard Mark I failed rarely. In the end, tube-based CPUs became dominant because the significant speed advantages afforded outweighed the reliability problems. Most of these early synchronous CPUs ran at low clock rates compared to modern microelectronic designs. Clock signal frequencies ranging from 100 kHz to 4 MHz were common at this time, limited by the speed of the switching de
A patent is a form of intellectual property. A patent gives its owner the right to exclude others from making, using and importing an invention for a limited period of time twenty years; the patent rights are granted in exchange for an enabling public disclosure of the invention. In most countries patent rights fall under civil law and the patent holder needs to sue someone infringing the patent in order to enforce his or her rights. In some industries patents are an essential form of competitive advantage; the procedure for granting patents, requirements placed on the patentee, the extent of the exclusive rights vary between countries according to national laws and international agreements. However, a granted patent application must include one or more claims that define the invention. A patent may include many claims; these claims must meet relevant patentability requirements, such as novelty and non-obviousness. Under the World Trade Organization's TRIPS Agreement, patents should be available in WTO member states for any invention, in all fields of technology, provided they are new, involve an inventive step, are capable of industrial application.
There are variations on what is patentable subject matter from country to country among WTO member states. TRIPS provides that the term of protection available should be a minimum of twenty years; the word patent originates from the Latin patere, which means "to lay open". It is a shortened version of the term letters patent, an open document or instrument issued by a monarch or government granting exclusive rights to a person, predating the modern patent system. Similar grants included land patents, which were land grants by early state governments in the USA, printing patents, a precursor of modern copyright. In modern usage, the term patent refers to the right granted to anyone who invents something new and non-obvious; some other types of intellectual property rights are called patents in some jurisdictions: industrial design rights are called design patents in the US, plant breeders' rights are sometimes called plant patents, utility models and Gebrauchsmuster are sometimes called petty patents or innovation patents.
The additional qualification utility patent is sometimes used to distinguish the primary meaning from these other types of patents. Particular species of patents for inventions include biological patents, business method patents, chemical patents and software patents. Although there is some evidence that some form of patent rights was recognized in Ancient Greece in the Greek city of Sybaris, the first statutory patent system is regarded to be the Venetian Patent Statute of 1474. Patents were systematically granted in Venice as of 1474, where they issued a decree by which new and inventive devices had to be communicated to the Republic in order to obtain legal protection against potential infringers; the period of protection was 10 years.. As Venetians emigrated, they sought similar patent protection in their new homes; this led to the diffusion of patent systems to other countries. The English patent system evolved from its early medieval origins into the first modern patent system that recognised intellectual property in order to stimulate invention.
By the 16th century, the English Crown would habitually abuse the granting of letters patent for monopolies. After public outcry, King James I of England was forced to revoke all existing monopolies and declare that they were only to be used for "projects of new invention"; this was incorporated into the Statute of Monopolies in which Parliament restricted the Crown's power explicitly so that the King could only issue letters patent to the inventors or introducers of original inventions for a fixed number of years. The Statute became the foundation for developments in patent law in England and elsewhere. Important developments in patent law emerged during the 18th century through a slow process of judicial interpretation of the law. During the reign of Queen Anne, patent applications were required to supply a complete specification of the principles of operation of the invention for public access. Legal battles around the 1796 patent taken out by James Watt for his steam engine, established the principles that patents could be issued for improvements of an existing machine and that ideas or principles without specific practical application could legally be patented.
Influenced by the philosophy of John Locke, the granting of patents began to be viewed as a form of intellectual property right, rather than the obtaining of economic privilege. The English legal system became the foundation for patent law in countries with a common law heritage, including the United States, New Zealand and Australia. In the Thirteen Colonies, inventors could obtain patents through petition to a given colony's legislature. In 1641, Samuel Winslow was granted the first patent in North America by the Massachusetts General Court for a new process for making salt; the modern French patent system was created during the Revolution in 1791. Patents were granted without examination. Patent costs were high. Importation patents protected new devices coming from foreign countries; the patent law was revised in 1844 - patent cost was lowered and importation patents were abolished. The first Patent Act of the U. S. Congress was passed on April 10, 1790, titled "An Act to promote the progress of
Dual-tone multi-frequency signaling
Dual-tone multi-frequency signaling is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States, became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized as ITU-T Recommendation Q.23. It is known in the UK as MF4; the Touch-Tone system using a telephone keypad replaced the use of rotary dial and has become the industry standard for landline and mobile service. Other multi-frequency systems are used for internal signaling within the telephone network. Prior to the development of DTMF, telephone numbers were dialed by users with a loop-disconnect signaling, more known as pulse dialing in the U. S, it functions by interrupting the current in the local loop between the telephone exchange and the calling party's telephone at a precise rate with a switch in the telephone, operated by the rotary dial as it spins back to its rest position after having been rotated to each desired number.
The exchange equipment responds to the dial pulses either directly by operating relays, or by storing the number in a digit register recording the dialed number. The physical distance for which this type of dialing was possible was restricted by electrical distortions and was only possible on direct metallic links between end points of a line. Placing calls over longer distances required either operator assistance or provision of special subscriber trunk dialing equipment. Operators used an earlier type of multi-frequency signaling. Multi-frequency signaling is a group of signaling methods that use a mixture of two pure tone sounds. Various MF signaling protocols were devised by the Bell System and CCITT; the earliest of these were for in-band signaling between switching centers, where long-distance telephone operators used a 16-digit keypad to input the next portion of the destination telephone number in order to contact the next downstream long-distance telephone operator. This semi-automated signaling and switching proved successful in both cost effectiveness.
Based on this prior success with using MF by specialists to establish long-distance telephone calls, dual-tone multi-frequency signaling was developed for end-user signaling without the assistance of operators. The DTMF system uses a set of eight audio frequencies transmitted in pairs to represent 16 signals, represented by the ten digits, the letters A to D, the symbols # and *; as the signals are audible tones in the voice frequency range, they can be transmitted through electrical repeaters and amplifiers, over radio and microwave links, thus eliminating the need for intermediate operators on long-distance circuits. AT&T described the product as "a method for pushbutton signaling from customer stations using the voice transmission path." In order to prevent consumer telephones from interfering with the MF-based routing and switching between telephone switching centers, DTMF frequencies differ from all of the pre-existing MF signaling protocols between switching centers: MF/R1, R2, CCS4, CCS5, others that were replaced by SS7 digital signaling.
DTMF was known throughout the Bell System by the trademark Touch-Tone. The term was first used by AT&T in commerce on July 5, 1960 and was introduced to the public on November 18, 1963, when the first push-button telephone was made available to the public, it was a registered trademark by AT&T from September 4, 1962 to March 13, 1984. It is standardized by ITU-T Recommendation Q.23. In the UK, it is known as MF4. Other vendors of compatible telephone equipment called the Touch-Tone feature tone dialing or DTMF, or used their other trade names such as Digitone by Northern Electric Company in Canada; as a method of in-band signaling, DTMF signals were used by cable television broadcasters to indicate the start and stop times of local commercial insertion points during station breaks for the benefit of cable companies. Until out-of-band signaling equipment was developed in the 1990s, unacknowledged DTMF tone sequences could be heard during the commercial breaks of cable channels in the United States and elsewhere.
Terrestrial television stations used DTMF tones to control remote transmitters. In IP telephony, DTMF signals can be delivered as either in-band or out-of-band tones, or as a part of signaling protocols, as long as both endpoints agree on a common approach to adopt; the engineers had envisioned telephones being used to access computers and automated response systems. They consulted with companies to determine the requirements; this led to the addition of the number sign and asterisk or "star" keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, it was many years before the two symbol keys became used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID. Public payphones that accept credit cards use these additional codes to send the information from the magnetic strip; the AUTOVON telephone system of the United States Armed Forces used these signals to assert certain privilege and priority levels when placing telephone calls.
Precedence is still a feature of military telephone networks. For example, entering 93 before a number is a priority call. Present-day uses of the A, B, C and D signals on telephone networks are few, are exclusive to network control. For example, the A key is used