A computer program is a collection of instructions that performs a specific task when executed by a computer. A computer requires programs to function. A computer program is written by a computer programmer in a programming language. From the program in its human-readable form of source code, a compiler can derive machine code—a form consisting of instructions that the computer can directly execute. Alternatively, a computer program may be executed with the aid of an interpreter. A collection of computer programs and related data are referred to as software. Computer programs may be categorized along functional lines, such as application software and system software; the underlying method used for some calculation or manipulation is known as an algorithm. The earliest programmable machines preceded the invention of the digital computer. In 1801, Joseph-Marie Jacquard devised a loom that would weave a pattern by following a series of perforated cards. Patterns could be repeated by arranging the cards.
In 1837, Charles Babbage was inspired by Jacquard's loom to attempt to build the Analytical Engine. The names of the components of the calculating device were borrowed from the textile industry. In the textile industry, yarn was brought from the store to be milled; the device would have had a "store"—memory to hold 1,000 numbers of 40 decimal digits each. Numbers from the "store" would have been transferred to the "mill", for processing, and a "thread" being the execution of programmed instructions by the device. It was programmed using two sets of perforated cards—one to direct the operation and the other for the input variables. However, after more than 17,000 pounds of the British government's money, the thousands of cogged wheels and gears never worked together. During a nine-month period in 1842–43, Ada Lovelace translated the memoir of Italian mathematician Luigi Menabrea; the memoir covered the Analytical Engine. The translation contained Note G which detailed a method for calculating Bernoulli numbers using the Analytical Engine.
This note is recognized by some historians as the world's first written computer program. In 1936, Alan Turing introduced the Universal Turing machine—a theoretical device that can model every computation that can be performed on a Turing complete computing machine, it is a finite-state machine. The machine can move the tape forth, changing its contents as it performs an algorithm; the machine starts in the initial state, goes through a sequence of steps, halts when it encounters the halt state. This machine is considered by some to be the origin of the stored-program computer—used by John von Neumann for the "Electronic Computing Instrument" that now bears the von Neumann architecture name; the Z3 computer, invented by Konrad Zuse in Germany, was a programmable computer. A digital computer uses electricity as the calculating component; the Z3 contained 2,400 relays to create the circuits. The circuits provided a floating-point, nine-instruction computer. Programming the Z3 was through a specially designed keyboard and punched tape.
The Electronic Numerical Integrator And Computer was a Turing complete, general-purpose computer that used 17,468 vacuum tubes to create the circuits. At its core, it was a series of Pascalines wired together, its 40 units weighed 30 tons, occupied 1,800 square feet, consumed $650 per hour in electricity when idle. It had 20 base-10 accumulators. Programming the ENIAC took up to two months. Three function tables needed to be rolled to fixed function panels. Function tables were connected to function panels using heavy black cables; each function table had 728 rotating knobs. Programming the ENIAC involved setting some of the 3,000 switches. Debugging a program took a week; the programmers of the ENIAC were women who were known collectively as the "ENIAC girls." The ENIAC featured parallel operations. Different sets of accumulators could work on different algorithms, it used punched card machines for input and output, it was controlled with a clock signal. It ran for eight years, calculating hydrogen bomb parameters, predicting weather patterns, producing firing tables to aim artillery guns.
The Manchester Baby was a stored-program computer. Programming transitioned away from setting dials. Only three bits of memory were available to store each instruction, so it was limited to eight instructions. 32 switches were available for programming. Computers manufactured; the computer program was written on paper for reference. An instruction was represented by a configuration of on/off settings. After setting the configuration, an execute button was pressed; this process was repeated. Computer programs were manually input via paper tape or punched cards. After the medium was loaded, the starting address was set via switches and the execute button pressed. In 1961, the Burroughs B5000 was built to be programmed in the ALGOL 60 language; the hardware featured circuits to ease the compile phase. In 1964, the IBM System/360 was a line of six computers each having the same instruction set architecture; the Model 30 was the least expensive. Customers could retain the same application software; each System/360 model featured multiprogramming.
With operating system support, multiple programs could be in memory at once. When one was waiting for input/output, another could compute; each model could emulate other computers. Customers could upgrade to the System/360 and ret
James Madison University
James Madison University is a public research university in Harrisonburg, Virginia. Founded in 1908 as the State Normal and Industrial School for Women at Harrisonburg, the institution was renamed Madison College in 1938 in honor of President James Madison and James Madison University in 1977; the university is situated in the Shenandoah Valley, with the campus quadrangle located on South Main Street. Founded in 1908 as a women's college, James Madison University was established by the Virginia General Assembly, it was called The State Normal and Industrial School for Women at Harrisonburg. In 1914, the name of the university was changed to the State Normal School for Women at Harrisonburg. At first, academic offerings included only today's equivalent of technical training or junior college courses. During this initial period of development, the campus plan was established and six buildings were constructed; the university became the State Teachers College at Harrisonburg in 1924 and continued under that name until 1938, when it was named Madison College in honor of James Madison, the fourth President of the United States whose Montpelier estate is located in nearby Orange, Virginia.
In 1976, the university's name was changed to James Madison University. The first president of the university was Julian Ashby Burruss; the university opened its doors to its first student body in 1909 with an enrollment of 209 students and a faculty of 15. Its first 20 graduates received diplomas in 1911. In 1919, Julian Burruss resigned the presidency to become president of Virginia Polytechnic Institute. Samuel Page Duke was chosen as the second president of the university. During Duke's administration, nine major buildings were constructed. Duke served as president from 1919 to 1949. In 1946, men were first enrolled as regular day students. G. Tyler Miller became the third president of the university in 1949, following the retirement of Samuel Duke. During Miller's administration, from 1949 to 1970, the campus was enlarged by 240 acres and 19 buildings were constructed. Major curriculum changes were made and the university was authorized to grant master's degrees in 1954. In 1966, by action of the Virginia General Assembly, the university became a coeducational institution.
Ronald E. Carrier, JMU's fourth president, headed the institution from 1971 to 1998. During Carrier's administration, student enrollment and the number of faculty and staff tripled, doctoral programs were authorized, more than twenty major campus buildings were constructed and the university was recognized by national publications as one of the finest institutions of its type in America. Carrier Library is named after him. During the first decade of the 21st century, during the administration of JMU's fifth President Linwood H. Rose, the university continued to expand, not only through new construction east of Interstate 81, but on the west side of campus. In early 2005, JMU purchased the Rockingham Memorial Hospital campus just north of the main JMU campus for over $40 million; the hospital has since moved to a new location, JMU now occupies the former hospital site after having made substantial renovations to the previous hospital campus. Additionally in June 2005, the university expanded across South High Street by leasing the former Harrisonburg High School building from the City of Harrisonburg.
In May 2006, the university purchased the property. The sale was approved in June 2005 for $17 million; the university named the old HHS building Memorial Hall. Completed projects include the Rose Library located on the east side of campus, which opened on August 11, 2008; the John C. Wells Planetarium, first opened in 1974, underwent a $1.5 million renovation in 2008. It is now the only one of its kind in the world; the mission of the JMU Planetarium is public outreach. As such, it offers free shows to the public every Saturday afternoon and hosts annual summer space camps in July; the 175,000-square-foot Forbes Center for the Performing Arts opened in June 2010, serves as the home to JMU's School of Theatre and Dance. It provides major performance venues and support spaces for the School of Music, the administrative office for the Dean of the College of Visual and Performing Arts; the rapid expansion of JMU's campus has at times created tension in the city-university relationship. In 2006, the local ABC affiliate reported that the university had nearly doubled in size in the last 20 years, including purchases of several local properties.
The university has experienced tension with local residents with occasional clashes between local police and students at a popular off-campus block party. In 2000, the party with about 2,500 students grew out of hand and required a police presence at the Forest Hills townhouse complex on Village Lane. Ten years police equipped with riot gear used force to disperse a group of 8,000 college-aged individuals at the party. Several participants were airlifted to a medical center in Charlottesville to treat their injuries; the university has condemned the behavior of the block party attendees. James Madison University is considered "More Selective" by the Carnegie Foundation for the Advancement of Teaching. For the Class of 2012, the university received 22,648 applications, for an entering freshmen class of 4,325 for the 2012–2013 academic year; the retention rate for the 2011–2012 freshman class was 91.4%, the ratio of female to male students is 60/40. 38% of students are from out-of-state, representing all 50 states and 89 foreign countries.
James Madison University offers 115 degree programs on the bac
A smart card, chip card, or integrated circuit card is a physical electronic authorization device, used to control access to a resource. It is a plastic credit card sized card with an embedded integrated circuit. Many smart cards include a pattern of metal contacts to electrically connect to the internal chip. Others are contactless, some are both. Smart cards can provide personal identification, data storage, application processing. Applications include identification, mobile phones, public transit, computer security and healthcare. Smart cards may provide strong security authentication for single sign-on within organizations. Several nations have deployed smart cards throughout their populations. In 1968 and 1969 Helmut Gröttrup and Jürgen Dethloff jointly filed patents for the automated chip card. Roland Moreno patented the memory card concept in 1974. An important patent for smart cards with a microprocessor and memory as used today was filed by Jürgen Dethloff in 1976 and granted as USP 4105156 in 1978.
In 1977, Michel Ugon from Honeywell Bull invented the first microprocessor smart card with two chips: one microprocessor and one memory, in 1978, he patented the self-programmable one-chip microcomputer that defines the necessary architecture to program the chip. Three years Motorola used this patent in its "CP8". At that time, Bull had 1,200 patents related to smart cards. In 2001, Bull sold its CP8 division together with its patents to Schlumberger, who subsequently combined its own internal smart card department and CP8 to create Axalto. In 2006, Axalto and Gemplus, at the time the world's top two smart-card manufacturers and became Gemalto. In 2008, Dexa Systems spun off from Schlumberger and acquired Enterprise Security Services business, which included the smart-card solutions division responsible for deploying the first large-scale smart-card management systems based on public key infrastructure; the first mass use of the cards was as a telephone card for payment in French payphones, starting in 1983.
After the Télécarte, microchips were integrated into all French Carte Bleue debit cards in 1992. Customers inserted the card into the merchant's point-of-sale terminal typed the personal identification number, before the transaction was accepted. Only limited transactions are processed without a PIN. Smart-card-based "electronic purse" systems store funds on the card, so that readers do not need network connectivity, they entered European service in the mid-1990s. They have been common in Germany, Belgium, the Netherlands, Norway, Sweden, Finland, UK, Denmark and Portugal. Private electronic purse systems have been deployed such as the Marines corps at Parris Island allowing small amount payments at the cafeteria. Since the 1990s, smart cards have been the subscriber identity modules used in GSM mobile-phone equipment. Mobile phones are used across the world, so smart cards have become common. Europay MasterCard Visa -compliant cards and equipment are widespread with the deployment led by European countries.
The United States started deploying the EMV technology in 2014, with the deployment still in progress in 2018. A country's national payment association, in coordination with MasterCard International, Visa International, American Express and Japan Credit Bureau, jointly plan and implement EMV systems. In 1993 several international payment companies agreed to develop smart-card specifications for debit and credit cards; the original brands were MasterCard and Europay. The first version of the EMV system was released in 1994. In 1998 the specifications became stable. EMVCo maintains these specifications. EMVco's purpose is to assure the various financial institutions and retailers that the specifications retain backward compatibility with the 1998 version. EMVco upgraded the specifications in 2000 and 2004. EMV compliant cards were first accepted into Malaysia in 2005 and into United States in 2014. MasterCard was the first company, allowed to use the technology in the United States; the United States has felt pushed to use the technology because of the increase in identity theft.
The credit card information stolen from Target in late 2013 was one of the largest indicators that American credit card information is not safe. Target made the decision on April 30, 2014 that it would try to implement the smart chip technology in order to protect itself from future credit card identity theft. Before 2014, the consensus in America was that there were enough security measures to avoid credit card theft and that the smart chip was not necessary; the cost of the smart chip technology was significant, why most of the corporations did not want to pay for it in the United States. The debate came when online credit theft was insecure enough for the United States to invest in the technology; the adaptation of EMV's increased in 2015 when the liability shifts occurred in October by the credit card companies. Contactless smart cards do not require physical contact between a reader, they are becoming more popular for ticketing. Typical uses include mass motorway tolls. Visa and MasterCard implemented a version deployed in 2004–2006 in the U.
S. with Visa's current offering called Visa Contactless. Most contactless fare collection systems are incompatible, though the MIFARE Standard card from NXP Semiconductors has a considerable mark
PowerPC is a reduced instruction set computing instruction set architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM. PowerPC, as an evolving instruction set, has since 2006 been named Power ISA, while the old name lives on as a trademark for some implementations of Power Architecture-based processors. PowerPC was the cornerstone of AIM's PReP and Common Hardware Reference Platform initiatives in the 1990s. Intended for personal computers, the architecture is well known for being used by Apple's Power Macintosh, PowerBook, iMac, iBook, Xserve lines from 1994 until 2006, when Apple migrated to Intel's x86, it has since become a niche in personal computers, but remains popular for embedded and high-performance processors. Its use in 7th generation of video game consoles and embedded applications provided an array of uses. In addition, PowerPC CPUs are still used in third party AmigaOS 4 personal computers. PowerPC is based on IBM's earlier POWER instruction set architecture, retains a high level of compatibility with it.
The history of RISC began with IBM's 801 research project, on which John Cocke was the lead developer, where he developed the concepts of RISC in 1975–78. 801-based microprocessors were used in a number of IBM embedded products becoming the 16-register IBM ROMP processor used in the IBM RT PC. The RT PC was a rapid design implementing the RISC architecture. Between the years of 1982–1984, IBM started a project to build the fastest microprocessor on the market; the result is the POWER instruction set architecture, introduced with the RISC System/6000 in early 1990. The original POWER microprocessor, one of the first superscalar RISC implementations, is a high performance, multi-chip design. IBM soon realized that a single-chip microprocessor was needed in order to scale its RS/6000 line from lower-end to high-end machines. Work began on a one-chip POWER microprocessor, designated the RSC. In early 1991, IBM realized its design could become a high-volume microprocessor used across the industry. Apple had realized the limitations and risks of its dependency upon a single CPU vendor at a time when Motorola was falling behind on delivering the 68040 CPU.
Furthermore, Apple had conducted its own research and made an experimental quad-core CPU design called Aquarius, which convinced the company's technology leadership that the future of computing was in the RISC methodology. IBM approached Apple with the goal of collaborating on the development of a family of single-chip microprocessors based on the POWER architecture. Soon after, being one of Motorola's largest customers of desktop-class microprocessors, asked Motorola to join the discussions due to their long relationship, Motorola having had more extensive experience with manufacturing high-volume microprocessors than IBM, to form a second source for the microprocessors; this three-way collaboration between Apple, IBM, Motorola became known as the AIM alliance. In 1991, the PowerPC was just one facet of a larger alliance among these three companies. At the time, most of the personal computer industry was shipping systems based on the Intel 80386 and 80486 chips, which have a complex instruction set computer architecture, development of the Pentium processor was well underway.
The PowerPC chip was one of several joint ventures involving the three alliance members, in their efforts to counter the growing Microsoft-Intel dominance of personal computing. For Motorola, POWER looked like an unbelievable deal, it allowed the company to sell a tested and powerful RISC CPU for little design cash on its own part. It maintained ties with an important customer and seemed to offer the possibility of adding IBM too, which might buy smaller versions from Motorola instead of making its own. At this point Motorola had its own RISC design in the form of the 88000, doing poorly in the market. Motorola was doing well with its 68000 family and the majority of the funding was focused on this; the 88000 effort was somewhat starved for resources. The 88000 was in production, however; the 88000 had achieved a number of embedded design wins in telecom applications. If the new POWER one-chip version could be made bus-compatible at a hardware level with the 88000, that would allow both Apple and Motorola to bring machines to market far faster since they would not have to redesign their board architecture.
The result of these various requirements is the PowerPC specification. The differences between the earlier POWER instruction set and that of PowerPC is outlined in Appendix E of the manual for PowerPC ISA v.2.02. Since 1991, IBM had a long-standing desire for a unifying operating system that would host all existing operating systems as personalities upon one microkernel. From 1991 to 1995, the company designed and aggressively evangelized what would become Workplace OS targeting PowerPC; when the first PowerPC products reached the market, they were met with enthusiasm. In addition to Apple, both IBM and the Motorola Computer Group offered systems built around the processors. Microsoft released Windows NT 3.51 for the architecture, used in Motorola's
DOS is a family of disk operating systems, hence the name. DOS consists of MS-DOS and a rebranded version under the name IBM PC DOS, both of which were introduced in 1981. Other compatible systems from other manufacturers include DR-DOS, ROM-DOS, PTS-DOS, FreeDOS. MS-DOS dominated the x86-based IBM PC compatible market between 1981 and 1995. Dozens of other operating systems use the acronym "DOS", including the mainframe DOS/360 from 1966. Others are Apple DOS, Apple ProDOS, Atari DOS, Commodore DOS, TRSDOS, AmigaDOS. Fictional operating systems have used this acronym as well, such as GLaDOS from the video game Portal. IBM PC DOS and its predecessor, 86-DOS, resembled Digital Research's CP/M—the dominant disk operating system for 8-bit Intel 8080 and Zilog Z80 microcomputers—but instead ran on Intel 8086 16-bit processors; when IBM introduced the IBM PC, built with the Intel 8088 microprocessor, they needed an operating system. Seeking an 8088-compatible build of CP/M, IBM approached Microsoft CEO Bill Gates.
IBM was sent to Digital Research, a meeting was set up. However, the initial negotiations for the use of CP/M broke down. Digital Research founder Gary Kildall refused, IBM withdrew. IBM again approached Bill Gates. Gates in turn approached Seattle Computer Products. There, programmer Tim Paterson had developed a variant of CP/M-80, intended as an internal product for testing SCP's new 16-bit Intel 8086 CPU card for the S-100 bus; the system was named QDOS, before being made commercially available as 86-DOS. Microsoft purchased 86-DOS for $50,000; this became Microsoft Disk Operating System, MS-DOS, introduced in 1981. Within a year Microsoft licensed MS-DOS to over 70 other companies, which supplied the operating system for their own hardware, sometimes under their own names. Microsoft required the use of the MS-DOS name, with the exception of the IBM variant. IBM continued to develop their version, PC DOS, for the IBM PC. Digital Research became aware that an operating system similar to CP/M was being sold by IBM, threatened legal action.
IBM responded by offering an agreement: they would give PC consumers a choice of PC DOS or CP/M-86, Kildall's 8086 version. Side-by-side, CP/M cost $200 more than PC DOS, sales were low. CP/M faded, with MS-DOS and PC DOS becoming the marketed operating system for PCs and PC compatibles. Microsoft sold MS-DOS only to original equipment manufacturers. One major reason for this was. DOS was structured such that there was a separation between the system specific device driver code and the DOS kernel. Microsoft provided an OEM Adaptation Kit which allowed OEMs to customize the device driver code to their particular system. By the early 1990s, most PCs adhered to IBM PC standards so Microsoft began selling MS-DOS in retail with MS-DOS 5.0. In the mid-1980s Microsoft developed a multitasking version of DOS; this version of DOS is referred to as "European MS-DOS 4" because it was developed for ICL and licensed to several European companies. This version of DOS supports preemptive multitasking, shared memory, device helper services and New Executable format executables.
None of these features were used in versions of DOS, but they were used to form the basis of the OS/2 1.0 kernel. This version of DOS is distinct from the released PC DOS 4.0, developed by IBM and based upon DOS 3.3. Digital Research attempted to regain the market lost from CP/M-86 with Concurrent DOS, FlexOS and DOS Plus with Multiuser DOS and DR DOS. Digital Research was bought by Novell, DR DOS became Novell DOS 7. Gordon Letwin wrote in 1995 that "DOS was, when we first wrote it, a one-time throw-away product intended to keep IBM happy so that they'd buy our languages". Microsoft expected; the company planned to over time improve MS-DOS so it would be indistinguishable from single-user Xenix, or XEDOS, which would run on the Motorola 68000, Zilog Z-8000, LSI-11. IBM, did not want to replace DOS. After AT&T began selling Unix, Microsoft and IBM began developing OS/2 as an alternative; the two companies had a series of disagreements over two successor operating systems to DOS, OS/2 and Windows.
They split development of their DOS systems as a result. The last retail version of MS-DOS was MS-DOS 6.22. The last retail version of PC DOS was PC DOS 2000, though IBM did develop PC DOS 7.10 for OEMs and internal use. The FreeDOS project began on 26 June 1994, when Microsoft announced it would no longer sell or support MS-DOS. Jim Hall posted a manifesto proposing the development of an open-source replacement. Within a few weeks, other programmers including Pat Villani and Tim Norman joined the project. A kernel, the COMMAND. COM command line interpreter, core utilities were created by pooling code they had wri
Optimal asymmetric encryption padding
In cryptography, Optimal Asymmetric Encryption Padding is a padding scheme used together with RSA encryption. OAEP was introduced by Bellare and Rogaway, subsequently standardized in PKCS#1 v2 and RFC 2437; the OAEP algorithm is a form of Feistel network which uses a pair of random oracles G and H to process the plaintext prior to asymmetric encryption. When combined with any secure trapdoor one-way permutation f, this processing is proved in the random oracle model to result in a combined scheme, semantically secure under chosen plaintext attack; when implemented with certain trapdoor permutations, OAEP is proved secure against chosen ciphertext attack. OAEP can be used to build an all-or-nothing transform. OAEP satisfies the following two goals: Add an element of randomness which can be used to convert a deterministic encryption scheme into a probabilistic scheme. Prevent partial decryption of ciphertexts by ensuring that an adversary cannot recover any portion of the plaintext without being able to invert the trapdoor one-way permutation f.
The original version of OAEP showed a form of "plaintext awareness" in the random oracle model when OAEP is used with any trapdoor permutation. Subsequent results contradicted this claim. However, the original scheme was proved in the random oracle model to be IND-CCA2 secure when OAEP is used with the RSA permutation using standard encryption exponents, as in the case of RSA-OAEP. An improved scheme that works with any trapdoor one-way permutation was offered by Victor Shoup to solve this problem. More recent work has shown that in the standard model it is impossible to prove the IND-CCA2 security of RSA-OAEP under the assumed hardness of the RSA problem. In the diagram, n is the number of bits in the RSA modulus. K0 and k1 are integers fixed by the protocol. M is the plaintext message, an -bit string G and H are random oracles such as cryptographic hash functions. ⊕ is an xor operation. To encode, messages are padded with k1 zeros to be n − k0 bits in length. R is a randomly generated k0-bit string.
X = m00..0 ⊕ G H reduces the n − k0 bits of X to k0 bits. Y = r ⊕ H The output is X || Y where X is shown in the diagram as the leftmost block and Y as the rightmost block. To decode, recover the random string as r = Y ⊕ H recover the message as m00..0 = X ⊕ G The "all-or-nothing" security is from the fact that to recover m, one must recover the entire X and the entire Y. Since any changed bit of a cryptographic hash changes the result, the entire X, the entire Y must both be recovered. In the PKCS#1 standard, the random oracles G and H are identical; the PKCS#1 standard further requires that the random oracles be MGF1 with an appropriate hash function. Key encapsulation
Bulletin board system
A bulletin board system or BBS is a computer server running software that allows users to connect to the system using a terminal program. Once logged in, the user can perform functions such as uploading and downloading software and data, reading news and bulletins, exchanging messages with other users through public message boards and sometimes via direct chatting. In the middle to late 1980s, message aggregators and bulk store-and-forward'ers sprung up to provide services such as FidoNet, similar to email. Many BBSes offer online games in which users can compete with each other. BBSes with multiple phone lines provide chat rooms, allowing users to interact with each other. Bulletin board systems were in many ways a precursor to the modern form of the World Wide Web, social networks, other aspects of the Internet. Low-cost, high-performance modems drove the use of online services and BBSes through the early 1990s. Infoworld estimated that there were 60,000 BBSes serving 17 million users in the United States alone in 1994, a collective market much larger than major online services such as CompuServe.
The introduction of inexpensive dial-up internet service and the Mosaic web browser offered ease of use and global access that BBS and online systems did not provide, led to a rapid crash in the market starting in 1994. Over the next year, many of the leading BBS software providers went bankrupt and tens of thousands of BBSes disappeared. Today, BBSing survives as a nostalgic hobby in most parts of the world, but it is still an popular form of communication for Taiwanese youth. Most surviving BBSes are accessible over Telnet and offer free email accounts, FTP services, IRC and all the protocols used on the Internet; some offer access through packet switched networks or packet radio connections. A precursor to the public bulletin board system was Community Memory, started in August 1973 in Berkeley, California. Useful microcomputers did not exist at that time, modems were both expensive and slow. Community Memory therefore ran on a mainframe computer and was accessed through terminals located in several San Francisco Bay Area neighborhoods.
The poor quality of the original modem connecting the terminals to the mainframe prompted a user to invent the Pennywhistle modem, whose design was influential in the mid-1970s. Community Memory allowed the user to type messages into a computer terminal after inserting a coin, offered a "pure" bulletin board experience with public messages only, it did offer the ability to tag messages with keywords. The system acted in the form of a buy and sell system with the tags taking the place of the more traditional classifications, but users found ways to express themselves outside these bounds, the system spontaneously created stories and other forms of communications. The system was expensive to operate, when their host machine became unavailable and a new one could not be found, the system closed in January 1975. Similar functionality was available to most mainframe users, which might be considered a sort of ultra-local BBS when used in this fashion. Commercial systems, expressly intended to offer these features to the public, became available in the late 1970s and formed the online service market that lasted into the 1990s.
One influential example was PLATO, which had thousands of users by the late 1970s, many of whom used the messaging and chat room features of the system in the same way that would become common on BBSes. Early modems were very simple devices using acoustic couplers to handle telephone operation; the user would first pick up the phone, dial a number press the handset into rubber cups on the top of the modem. Disconnecting at the end of a call required the user to pick up the handset and return it to the phone. Examples of direct-connecting modems did exist, these allowed the host computer to send it commands to answer or hang up calls, but these were expensive devices used by large banks and similar companies. With the introduction of microcomputers with expansion slots, like the S-100 bus machines and Apple II, it became possible for the modem to communicate instructions and data on separate lines. A number of modems of this sort were available by the late 1970s; this made the BBS possible for the first time, as it allowed software on the computer to pick up an incoming call, communicate with the user, hang up the call when the user logged off.
The first public dial-up BBS was developed by Randy Suess. According to an early interview, when Chicago was snowed under during the Great Blizzard of 1978, the two began preliminary work on the Computerized Bulletin Board System, or CBBS; the system came into existence through a fortuitous combination of Christensen having a spare S-100 bus computer and an early Hayes internal modem, Suess's insistence that the machine be placed at his house in Chicago where it would be a local phone call to millions of users. Christensen patterned the system after the cork board his local computer club used to post information like "need a ride". CBBS went online on 16 February 1978. CBBS, which kept a count of callers connected 253,301 callers before it was retired. A key innovation required for the popularization of the BBS was the Smartmodem manufactured by Hayes Microcomputer Products. Internal modems like the ones used by CBBS and similar early systems were usable, but expensive due to the manufacturer having to make a different modem for every computer platform they wanted to target.
They were limited to those