123-451: In computer programming , a function (also procedure , method , subroutine , routine , or subprogram ) is a callable unit of software logic that has a well-defined interface and behavior and can be invoked multiple times. Callable units provide a powerful programming tool. The primary purpose is to allow for the decomposition of a large and/or complicated problem into chunks that have relatively low cognitive load and to assign
246-413: A call stack , a special case of the stack data structure , to implement function calls and returns. Each procedure call creates a new entry, called a stack frame , at the top of the stack; when the procedure returns, its stack frame is deleted from the stack, and its space may be used for other procedure calls. Each stack frame contains the private data of the corresponding call, which typically includes
369-790: A peripheral device , accessing a file , halting the program or the machine, or temporarily pausing program execution. Side effects are considered undesireble by Robert C. Martin , who is known for promoting design principles. Martin argues that side effects can result in temporal coupling or order dependencies. Computer programming Computer programming or coding is the composition of sequences of instructions, called programs , that computers can follow to perform tasks. It involves designing and implementing algorithms , step-by-step specifications of procedures, by writing code in one or more programming languages . Programmers typically use high-level programming languages that are more easily intelligible to humans than machine code , which
492-518: A book on the six female ENIAC programmers in 2022. These early programmers were drawn from a group of about two hundred women employed as computers at the Moore School of Electrical Engineering at the University of Pennsylvania. The job of computers was to produce the numeric result of mathematical formulas needed for a scientific study, or an engineering project. They usually did so with
615-402: A compiler can make it crash when parsing some large source file, a simplification of the test case that results in only few lines from the original source file can be sufficient to reproduce the same crash. Trial-and-error/divide-and-conquer is needed: the programmer will try to remove some parts of the original test case and check if the problem still exists. When debugging the problem in a GUI,
738-647: A dedicated hardware stack to store return addresses—such hardware supports only a few levels of subroutine nesting, but can support recursive subroutines. Machines before the mid-1960s—such as the UNIVAC I , the PDP-1 , and the IBM 1130 —typically use a calling convention which saved the instruction counter in the first memory location of the called subroutine. This allows arbitrarily deep levels of subroutine nesting but does not support recursive subroutines. The IBM System/360 had
861-417: A different name for a callable unit that returns a value ( function or subprogram ) vs. one that does not ( subroutine or procedure ). Other languages, such as C , C++ , C# and Lisp , use only one name for a callable unit, function . The C-family languages use the keyword void to indicate no return value. If declared to return a value, a call can be embedded in an expression in order to consume
984-468: A factor of five. In July 1953, a 100-word expansion core memory was added to the system, using binary-coded decimal , excess-3 number representation. To support this expansion memory, ENIAC was equipped with a new Function Table selector, a memory address selector, pulse-shaping circuits, and three new orders were added to the programming mechanism. Mechanical computing machines have been around since Archimedes ' time (see: Antikythera mechanism ), but
1107-477: A failure was 116 hours—close to five days. ENIAC could be programmed to perform complex sequences of operations, including loops, branches, and subroutines. However, instead of the stored-program computers that exist today, ENIAC was just a large collection of arithmetic machines, which originally had programs set up into the machine by a combination of plugboard wiring and three portable function tables (containing 1,200 ten-way switches each). The task of taking
1230-540: A few simple readability transformations made code shorter and drastically reduced the time to understand it. Following a consistent programming style often helps readability. However, readability is more than just programming style. Many factors, having little or nothing to do with the ability of the computer to efficiently compile and execute the code, contribute to readability. Some of these factors include: The presentation aspects of this (such as indents, line breaks, color highlighting, and so on) are often handled by
1353-421: A library, in the literal sense, which kept indexed collections of tapes or decks of cards for collective use. To remove the need for self-modifying code , computer designers eventually provided an indirect jump instruction, whose operand, instead of being the return address itself, was the location of a variable or processor register containing the return address. On those computers, instead of modifying
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#17327943265491476-454: A mechanical adding machine . ENIAC had 20 ten-digit signed accumulators , which used ten's complement representation and could perform 5,000 simple addition or subtraction operations between any of them and a source (e.g., another accumulator or a constant transmitter) per second. It was possible to connect several accumulators to run simultaneously, so the peak speed of operation was potentially much higher, due to parallel operation. It
1599-412: A mechanical calculator. The women studied the machine's logic, physical structure, operation, and circuitry in order to not only understand the mathematics of computing, but also the machine itself. This was one of the few technical job categories available to women at that time. Betty Holberton (née Snyder) continued on to help write the first generative programming system ( SORT/MERGE ) and help design
1722-443: A number to a register, read a number from a register, or add/subtract two numbers. A multiplication of a 10-digit number by a d -digit number (for d up to 10) took d +4 cycles, so the multiplication of a 10-digit number by 10-digit number took 14 cycles, or 2,800 microseconds—a rate of 357 per second. If one of the numbers had fewer than 10 digits, the operation was faster. Division and square roots took 13( d +1) cycles, where d
1845-435: A problem and mapping it onto the machine was complex, and usually took weeks. Due to the complexity of mapping programs onto the machine, programs were only changed after huge numbers of tests of the current program. After the program was figured out on paper, the process of getting the program into ENIAC by manipulating its switches and cables could take days. This was followed by a period of verification and debugging, aided by
1968-470: A result, loses efficiency and the ability for low-level manipulation). Debugging is a very important task in the software development process since having defects in a program can have significant consequences for its users. Some languages are more prone to some kinds of faults because their specification does not require compilers to perform as much checking as other languages. Use of a static code analysis tool can help detect some possible problems. Normally
2091-455: A sequence of numbers, and so on through the list of subroutines needed for a particular problem. ... All these subroutines will then be stored in the machine, and all one needs to do is make a brief reference to them by number, as they are indicated in the coding. Kay McNulty had worked closely with John Mauchly on the ENIAC team and developed an idea for subroutines for the ENIAC computer she
2214-558: A series of forty-eight lectures given in Philadelphia, Pennsylvania; all together called The Theory and Techniques for Design of Digital Computers —more often named the Moore School Lectures . Half of these lectures were given by the inventors of ENIAC. ENIAC was a one-of-a-kind design and was never repeated. The freeze on design in 1943 meant that it lacked some innovations that soon became well-developed, notably
2337-482: A special divider/square-rooter unit to perform up to 40 division operations per second or three square root operations per second. The other nine units in ENIAC were the initiating unit (started and stopped the machine), the cycling unit (used for synchronizing the other units), the master programmer (controlled loop sequencing), the reader (controlled an IBM punch-card reader), the printer (controlled an IBM card punch),
2460-425: A subroutine call instruction that placed the saved instruction counter value into a general-purpose register; this can be used to support arbitrarily deep subroutine nesting and recursive subroutines. The Burroughs B5000 (1961) is one of the first computers to store subroutine return data on a stack. The DEC PDP-6 (1964) is one of the first accumulator-based machines to have a subroutine call instruction that saved
2583-462: A subroutine called MYSUB from the main program. The subroutine would be coded as The JSB instruction placed the address of the NEXT instruction (namely, BB) into the location specified as its operand (namely, MYSUB), and then branched to the NEXT location after that (namely, AA = MYSUB + 1). The subroutine could then return to the main program by executing the indirect jump JMP MYSUB, I which branched to
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#17327943265492706-423: A technician. During World War II , while the U.S. Army needed to compute ballistics trajectories, many women were interviewed for this task. At least 200 women were hired by the Moore School of Engineering to work as " computers " and six of them were chosen to be the programmers of ENIAC. Betty Holberton , Kay McNulty , Marlyn Wescoff , Ruth Lichterman , Betty Jean Jennings , and Fran Bilas , programmed
2829-424: A ten-digit decimal number in memory. Numbers were passed between these units across several general-purpose buses (or trays , as they were called). In order to achieve its high speed, the panels had to send and receive numbers, compute, save the answer and trigger the next operation, all without any moving parts. Key to its versatility was the ability to branch ; it could trigger different operations, depending on
2952-459: A visual environment. Different programming languages support different styles of programming (called programming paradigms ). The choice of language used is subject to many considerations, such as company policy, suitability to task, availability of third-party packages, or individual preference. Ideally, the programming language best suited for the task at hand will be selected. Trade-offs from this ideal involve finding enough programmers who know
3075-410: Is Entity-Relationship Modeling ( ER Modeling ). Implementation techniques include imperative languages ( object-oriented or procedural ), functional languages , and logic programming languages. It is very difficult to determine what are the most popular modern programming languages. Methods of measuring programming language popularity include: counting the number of job advertisements that mention
3198-404: Is a callable unit in the source code and an associated one in the machine code, but they are different kinds of callable units – with different implications and features. The meaning of each callable term (function, procedure, method, ...) is, in fact, different. They are not synonymous . Nevertheless, they each add a capability to programming that has commonality. The term used tends to reflect
3321-607: Is directly executed by the central processing unit . Proficient programming usually requires expertise in several different subjects, including knowledge of the application domain , details of programming languages and generic code libraries , specialized algorithms, and formal logic . Auxiliary tasks accompanying and related to programming include analyzing requirements , testing , debugging (investigating and fixing problems), implementation of build systems , and management of derived artifacts , such as programs' machine code . While these are sometimes considered programming, often
3444-464: Is little more than a different notation for a machine language, two machines with different instruction sets also have different assembly languages. High-level languages made the process of developing a program simpler and more understandable, and less bound to the underlying hardware . The first compiler related tool, the A-0 System , was developed in 1952 by Grace Hopper , who also coined
3567-411: Is most obvious and objectionable in leaf procedures or leaf functions , which return without making any procedure calls themselves. To reduce that overhead, many modern compilers try to delay the use of a call stack until it is really needed. For example, the call of a procedure P may store the return address and parameters of the called procedure in certain processor registers, and transfer control to
3690-418: Is possible, since all the logical characteristics essential to this procedure are available, to evolve a coding instruction for placing the subroutines in the memory at places known to the machine, and in such a way that they may easily be called into use. In other words, one can designate subroutine A as division and subroutine B as complex multiplication and subroutine C as the evaluation of a standard error of
3813-451: Is similar to learning a foreign language . ENIAC ENIAC ( / ˈ ɛ n i æ k / ; Electronic Numerical Integrator and Computer ) was the first programmable , electronic , general-purpose digital computer , completed in 1945. Other computers had some of these features, but ENIAC was the first to have them all. It was Turing-complete and able to solve "a large class of numerical problems" through reprogramming. ENIAC
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3936-542: Is still strong in corporate data centers often on large mainframe computers , Fortran in engineering applications, scripting languages in Web development, and C in embedded software . Many applications use a mix of several languages in their construction and use. New languages are generally designed around the syntax of a prior language with new functionality added, (for example C++ adds object-orientation to C, and Java adds memory management and bytecode to C++, but as
4059-499: Is the number of digits in the result (quotient or square root). So a division or square root took up to 143 cycles, or 28,600 microseconds—a rate of 35 per second. (Wilkes 1956:20 states that a division with a 10-digit quotient required 6 milliseconds.) If the result had fewer than ten digits, it was obtained faster. ENIAC was able to process about 500 FLOPS , compared to modern supercomputers' petascale and exascale computing power. ENIAC used common octal-base radio tubes of
4182-401: Is used to declare no return value; for example void in C, C++ and C#. In some languages, such as Python, the difference is whether the body contains a return statement with a value, and a particular callable may return with or without a value based on control flow. In many contexts, a callable may have side effect behavior such as modifying passed or global data, reading from or writing to
4305-434: Is usually easier to code in "high-level" languages than in "low-level" ones. Programming languages are essential for software development. They are the building blocks for all software, from the simplest applications to the most sophisticated ones. Allen Downey , in his book How To Think Like A Computer Scientist , writes: Many computer languages provide a mechanism to call functions provided by shared libraries . Provided
4428-437: Is usually implemented as a contiguous area of memory. It is an arbitrary design choice whether the bottom of the stack is the lowest or highest address within this area, so that the stack may grow forwards or backwards in memory; however, many architectures chose the latter. Some designs, notably some Forth implementations, used two separate stacks, one mainly for control information (like return addresses and loop counters) and
4551-531: The Atanasoff–Berry computer (ABC), prototyped in 1939 by John Atanasoff and Clifford Berry – U.S. patent 3,120,606 for ENIAC, applied for in 1947 and granted in 1964, was voided by the 1973 decision of the landmark federal court case Honeywell, Inc. v. Sperry Rand Corp. . The decision included: that the ENIAC inventors had derived the subject matter of the electronic digital computer from Atanasoff; gave legal recognition to Atanasoff as
4674-504: The Jacquard loom could produce entirely different weaves by changing the "program" – a series of pasteboard cards with holes punched in them. Code-breaking algorithms have also existed for centuries. In the 9th century, the Arab mathematician Al-Kindi described a cryptographic algorithm for deciphering encrypted code, in A Manuscript on Deciphering Cryptographic Messages . He gave
4797-524: The execution of a program. Execution continues at the next instruction after the call instruction when it returns control. The features of implementations of callable units evolved over time and varies by context. This section describes features of the various common implementations. Most modern programming languages provide features to define and call functions, including syntax for accessing such features, including: Some languages, such as Pascal , Fortran , Ada and many dialects of BASIC , use
4920-439: The source code editor , but the content aspects reflect the programmer's talent and skills. Various visual programming languages have also been developed with the intent to resolve readability concerns by adopting non-traditional approaches to code structure and display. Integrated development environments (IDEs) aim to integrate all such help. Techniques like Code refactoring can enhance readability. The academic field and
5043-766: The 1930s and 1940s are considered the beginning of the modern computer era. ENIAC was, like the IBM Harvard Mark I and the German Z3 , able to run an arbitrary sequence of mathematical operations, but did not read them from a tape. Like the British Colossus , it was programmed by plugboard and switches. ENIAC combined full, Turing-complete programmability with electronic speed. The Atanasoff–Berry Computer (ABC), ENIAC, and Colossus all used thermionic valves (vacuum tubes) . ENIAC's registers performed decimal arithmetic, rather than binary arithmetic like
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5166-522: The 1990s Kleiman learned that most of the ENIAC programmers were not invited to the ENIAC’s 50th anniversary event. So she made it her mission to track them down and record their oral histories. The documentary, intended to inspire young women and men to get involved in programming. "They were shocked to be discovered," Kleiman says. "They were thrilled to be recognized, but had mixed impressions about how they felt about being ignored for so long." Kleiman released
5289-568: The 9th century, a programmable music sequencer was invented by the Persian Banu Musa brothers, who described an automated mechanical flute player in the Book of Ingenious Devices . In 1206, the Arab engineer Al-Jazari invented a programmable drum machine where a musical mechanical automaton could be made to play different rhythms and drum patterns, via pegs and cams . In 1801,
5412-478: The AE in 1837. In the 1880s, Herman Hollerith invented the concept of storing data in machine-readable form. Later a control panel (plug board) added to his 1906 Type I Tabulator allowed it to be programmed for different jobs, and by the late 1940s, unit record equipment such as the IBM 602 and IBM 604 , were programmed by control panels in a similar way, as were the first electronic computers . However, with
5535-708: The Army to fund the project, which put him in charge to oversee it for them. Assembly for the computer began in June 1944. ENIAC was designed by Ursinus College physics professor John Mauchly and J. Presper Eckert of the University of Pennsylvania, U.S. The team of design engineers assisting the development included Robert F. Shaw (function tables), Jeffrey Chuan Chu (divider/square-rooter), Thomas Kite Sharpless (master programmer), Frank Mural (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer) and Jack Davis (accumulators). Significant development work
5658-498: The Colossus machines were dismantled in 1945; the remaining two were used to decrypt Soviet messages by GCHQ until the 1960s. The public demonstration for ENIAC was developed by Snyder and Jennings who created a demo that would calculate the trajectory of a missile in 15 seconds, a task that would have taken several weeks for a human computer . For a variety of reasons – including Mauchly's June 1941 examination of
5781-448: The ENIAC to perform calculations for ballistics trajectories electronically for the Army's Ballistic Research Laboratory . While men having the same education and experience were designated as "professionals", these women were unreasonably designated as "subprofessionals", though they had professional degrees in mathematics, and were highly trained mathematicians. These women were not "refrigerator ladies", i.e., models posing in front of
5904-497: The IBM System/360 , for example, the branch instructions BAL or BALR, designed for procedure calling, would save the return address in a processor register specified in the instruction, by convention register 14. To return, the subroutine had only to execute an indirect branch instruction (BR) through that register. If the subroutine needed that register for some other purpose (such as calling another subroutine), it would save
6027-550: The U.S. Army calculate complex ballistics tables. The U.S. Army Ordnance accepted their plan, giving the University of Pennsylvania a six-months research contract for $ 61,700. The construction contract was signed on June 5, 1943; work on the computer began in secret at the University of Pennsylvania 's Moore School of Electrical Engineering the following month, under the code name "Project PX", with John Grist Brainerd as principal investigator. Herman H. Goldstine persuaded
6150-619: The Z3, the ABC and Colossus. Like the Colossus, ENIAC required rewiring to reprogram until April 1948. In June 1948, the Manchester Baby ran its first program and earned the distinction of first electronic stored-program computer . Though the idea of a stored-program computer with combined memory for program and data was conceived during the development of ENIAC, it was not initially implemented in ENIAC because World War II priorities required
6273-565: The ability to execute the program step by step. A programming tutorial for the modulo function using an ENIAC simulator gives an impression of what a program on the ENIAC looked like. ENIAC's six primary programmers, Kay McNulty , Betty Jennings , Betty Snyder , Marlyn Wescoff , Fran Bilas and Ruth Lichterman , not only determined how to input ENIAC programs, but also developed an understanding of ENIAC's inner workings. The programmers were often able to narrow bugs down to an individual failed tube which could be pointed to for replacement by
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#17327943265496396-584: The ability to store a program. Eckert and Mauchly started work on a new design, to be later called the EDVAC , which would be both simpler and more powerful. In particular, in 1944 Eckert wrote his description of a memory unit (the mercury delay line ) which would hold both the data and the program. John von Neumann, who was consulting for the Moore School on the EDVAC, sat in on the Moore School meetings at which
6519-545: The call stack mechanism can be viewed as the earliest and simplest method for automatic memory management . However, another advantage of the call stack method is that it allows recursive function calls , since each nested call to the same procedure gets a separate instance of its private data. In a multi-threaded environment, there is generally more than one stack. An environment that fully supports coroutines or lazy evaluation may use data structures other than stacks to store their activation records. One disadvantage of
6642-447: The call stack mechanism is the increased cost of a procedure call and its matching return. The extra cost includes incrementing and decrementing the stack pointer (and, in some architectures, checking for stack overflow ), and accessing the local variables and parameters by frame-relative addresses, instead of absolute addresses. The cost may be realized in increased execution time, or increased processor complexity, or both. This overhead
6765-439: The callable declares as formal parameters . A caller passes actual parameters , a.k.a. arguments , to match. Different programming languages provide different conventions for passing arguments. In some languages, such as BASIC, a callable has different syntax (i.e. keyword) for a callable that returns a value vs. one that does not. In other languages, the syntax is the same regardless. In some of these languages an extra keyword
6888-423: The chunks meaningful names (unless they are anonymous). Judicious application can reduce the cost of developing and maintaining software, while increasing its quality and reliability. Callable units are present at multiple levels of abstraction in the programming environment. For example, a programmer may write a function in source code that is compiled to machine code that implements similar semantics . There
7011-414: The circumstances. The first step in most formal software development processes is requirements analysis , followed by testing to determine value modeling, implementation, and failure elimination (debugging). There exist a lot of different approaches for each of those tasks. One approach popular for requirements analysis is Use Case analysis. Many programmers use forms of Agile software development where
7134-495: The code, making it easy to target varying machine instruction sets via compilation declarations and heuristics . Compilers harnessed the power of computers to make programming easier by allowing programmers to specify calculations by entering a formula using infix notation . Programs were mostly entered using punched cards or paper tape . By the late 1960s, data storage devices and computer terminals became inexpensive enough that programs could be created by typing directly into
7257-467: The computers. Text editors were also developed that allowed changes and corrections to be made much more easily than with punched cards . Whatever the approach to development may be, the final program must satisfy some fundamental properties. The following properties are among the most important: Using automated tests and fitness functions can help to maintain some of the aforementioned attributes. In computer programming, readability refers to
7380-548: The concept of the stored-program computer introduced in 1949, both programs and data were stored and manipulated in the same way in computer memory . Machine code was the language of early programs, written in the instruction set of the particular machine, often in binary notation. Assembly languages were soon developed that let the programmer specify instructions in a text format (e.g., ADD X, TOTAL), with abbreviations for each operation code and meaningful names for specifying addresses. However, because an assembly language
7503-420: The constant transmitter, and three function tables. The references by Rojas and Hashagen (or Wilkes) give more details about the times for operations, which differ somewhat from those stated above. The basic machine cycle was 200 microseconds (20 cycles of the 100 kHz clock in the cycling unit), or 5,000 cycles per second for operations on the 10-digit numbers. In one of these cycles, ENIAC could write
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#17327943265497626-407: The construction of a new generation of electronic computing machines, including Electronic Delay Storage Automatic Calculator (EDSAC) at Cambridge University, England and SEAC at the U.S. Bureau of Standards. A number of improvements were made to ENIAC after 1947, including a primitive read-only stored programming mechanism using the function tables as program ROM , after which programming
7749-401: The context in which it is used – usually based on the language being used. For example: The idea of a callable unit was initially conceived by John Mauchly and Kathleen Antonelli during their work on ENIAC and recorded in a January 1947 Harvard symposium on "Preparation of Problems for EDVAC -type Machines." Maurice Wilkes , David Wheeler , and Stanley Gill are generally credited with
7872-435: The current (2020) Army supercomputers Jean , Kay , and Betty are named after Jean Bartik (Betty Jennings), Kay McNulty , and Betty Snyder respectively. The "programmer" and "operator" job titles were not originally considered professions suitable for women. The labor shortage created by World War II helped enable the entry of women into the field. However, the field was not viewed as prestigious, and bringing in women
7995-446: The day; the decimal accumulators were made of 6SN7 flip-flops , while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions. Numerous 6L6s and 6V6s served as line drivers to drive pulses through cables between rack assemblies. Several tubes burned out almost every day, leaving ENIAC nonfunctional about half the time. Special high-reliability tubes were not available until 1948. Most of these failures, however, occurred during
8118-539: The demonstration were invited to the formal dedication nor to the celebratory dinner held afterwards. The original contract amount was $ 61,700; the final cost was almost $ 500,000 (approximately equivalent to $ 9,000,000 in 2023). It was formally accepted by the U.S. Army Ordnance Corps in July 1946. ENIAC was shut down on November 9, 1946, for a refurbishment and a memory upgrade, and was transferred to Aberdeen Proving Ground , Maryland in 1947. There, on July 29, 1947, it
8241-547: The development of ENIAC. Under Herman and Adele Goldstine 's direction, the computers studied ENIAC's blueprints and physical structure to determine how to manipulate its switches and cables, as programming languages did not yet exist. Though contemporaries considered programming a clerical task and did not publicly recognize the programmers' effect on the successful operation and announcement of ENIAC, McNulty, Jennings, Snyder, Wescoff, Bilas, and Lichterman have since been recognized for their contributions to computing. Three of
8364-470: The early 1980s, to discover the recalculation dependencies in a spreadsheet. Namely, a location was reserved in each cell to store the return address. Since circular references are not allowed for natural recalculation order, this allows a tree walk without reserving space for a stack in memory, which was very limited on small computers such as the IBM PC . Most modern implementations of a function call use
8487-510: The ease with which a human reader can comprehend the purpose, control flow , and operation of source code . It affects the aspects of quality above, including portability, usability and most importantly maintainability. Readability is important because programmers spend the majority of their time reading, trying to understand, reusing, and modifying existing source code, rather than writing new source code. Unreadable code often leads to bugs, inefficiencies, and duplicated code . A study found that
8610-400: The electronic speed of computation and the electromechanical speed of input/output, almost any real-world problem was completely I/O bound , even without making use of the original machine's parallelism. Most computations would still be I/O bound, even after the speed reduction imposed by this modification. Early in 1952, a high-speed shifter was added, which improved the speed for shifting by
8733-527: The engineering practice of computer programming are concerned with discovering and implementing the most efficient algorithms for a given class of problems. For this purpose, algorithms are classified into orders using Big O notation , which expresses resource use—such as execution time or memory consumption—in terms of the size of an input. Expert programmers are familiar with a variety of well-established algorithms and their respective complexities and use this knowledge to choose algorithms that are best suited to
8856-470: The first commercial electronic computers, the UNIVAC and the BINAC , alongside Jean Jennings. McNulty developed the use of subroutines in order to help increase ENIAC's computational capability. Herman Goldstine selected the programmers, whom he called operators, from the computers who had been calculating ballistics tables with mechanical desk calculators, and a differential analyzer prior to and during
8979-400: The first description of cryptanalysis by frequency analysis , the earliest code-breaking algorithm. The first computer program is generally dated to 1843 when mathematician Ada Lovelace published an algorithm to calculate a sequence of Bernoulli numbers , intended to be carried out by Charles Babbage 's Analytical Engine . However, Charles Babbage himself had written a program for
9102-404: The first step in debugging is to attempt to reproduce the problem. This can be a non-trivial task, for example as with parallel processes or some unusual software bugs. Also, specific user environment and usage history can make it difficult to reproduce the problem. After the bug is reproduced, the input of the program may need to be simplified to make it easier to debug. For example, when a bug in
9225-575: The formal invention of this concept, which they termed a closed sub-routine , contrasted with an open subroutine or macro . However, Alan Turing had discussed subroutines in a paper of 1945 on design proposals for the NPL ACE , going so far as to invent the concept of a return address stack . The idea of a subroutine was worked out after computing machines had already existed for some time. The arithmetic and conditional jump instructions were planned ahead of time and have changed relatively little, but
9348-422: The function's return jump, the calling program would store the return address in a variable so that when the function completed, it would execute an indirect jump that would direct execution to the location given by the predefined variable. Another advance was the jump to subroutine instruction, which combined the saving of the return address with the calling jump, thereby minimizing overhead significantly. In
9471-464: The functions in a library follow the appropriate run-time conventions (e.g., method of passing arguments ), then these functions may be written in any other language. Computer programmers are those who write computer software. Their jobs usually involve: Although programming has been presented in the media as a somewhat mathematical subject, some research shows that good programmers have strong skills in natural human languages, and that learning to code
9594-461: The girl computers do the work more rapidly and accurately than they would. This is due in large measure to the feeling among the engineers that their college and industrial experience is being wasted and thwarted by mere repetitive calculation." Following the initial six programmers, an expanded team of a hundred scientists was recruited to continue work on the ENIAC. Among these were several women, including Gloria Ruth Gordon . Adele Goldstine wrote
9717-525: The inventor of the first electronic digital computer; and put the invention of the electronic digital computer in the public domain . The main parts were 40 panels and three portable function tables (named A, B, and C). The layout of the panels was (clockwise, starting with the left wall): An IBM card reader was attached to Constant Transmitter panel 3 and an IBM card punch was attached to Printer Panel 2. The Portable Function Tables could be connected to Function Table 1, 2, and 3. Pieces of ENIAC are held by
9840-404: The language to build a team, the availability of compilers for that language, and the efficiency with which programs written in a given language execute. Languages form an approximate spectrum from "low-level" to "high-level"; "low-level" languages are typically more machine-oriented and faster to execute, whereas "high-level" languages are more abstract and easier to use but execute less quickly. It
9963-465: The language, the number of books sold and courses teaching the language (this overestimates the importance of newer languages), and estimates of the number of existing lines of code written in the language (this underestimates the number of users of business languages such as COBOL). Some languages are very popular for particular kinds of applications, while some languages are regularly used to write many different kinds of applications. For example, COBOL
10086-412: The location stored at location MYSUB. Compilers for Fortran and other languages could easily make use of these instructions when available. This approach supported multiple levels of calls; however, since the return address, parameters, and return values of a subroutine were assigned fixed memory locations, it did not allow for recursive calls. Incidentally, a similar method was used by Lotus 1-2-3 , in
10209-449: The machine for press photography, as then computer scientist undergrad Kathryn Kleiman discovered in her own research as opposed to what she was told by a historian in computing. However, some of the women did not receive recognition for their work on the ENIAC in their entire lifetimes. After the war ended, the women continued to work on the ENIAC. Their expertise made their positions difficult to replace with returning soldiers. Later In
10332-433: The machine to be completed quickly, and ENIAC's 20 storage locations would be too small to hold data and programs. The Z3 and Colossus were developed independently of each other, and of the ABC and ENIAC during World War II. Work on the ABC at Iowa State University was stopped in 1942 after John Atanasoff was called to Washington, D.C. , to do physics research for the U.S. Navy, and it was subsequently dismantled. The Z3
10455-491: The original technical description of the ENIAC. Several language systems were developed to describe programs for the ENIAC, including: Although the Ballistic Research Laboratory was the sponsor of ENIAC, one year into this three-year project John von Neumann , a mathematician working on the hydrogen bomb at Los Alamos National Laboratory , became aware of the ENIAC. In December 1945, the ENIAC
10578-495: The other for data. The former was, or worked like, a call stack and was only indirectly accessible to the programmer through other language constructs while the latter was more directly accessible. When stack-based procedure calls were first introduced, an important motivation was to save precious memory. With this scheme, the compiler does not have to reserve separate space in memory for the private data (parameters, return address, and local variables) of each procedure. At any moment,
10701-522: The procedure's body by a simple jump. If the procedure P returns without making any other call, the call stack is not used at all. If P needs to call another procedure Q , it will then use the call stack to save the contents of any registers (such as the return address) that will be needed after Q returns. In general, a callable unit is a list of instructions that, starting at the first instruction, executes sequentially except as directed via its internal logic. It can be invoked (called) many times during
10824-408: The procedure's parameters and internal variables, and the return address. The call sequence can be implemented by a sequence of ordinary instructions (an approach still used in reduced instruction set computing (RISC) and very long instruction word (VLIW) architectures), but many traditional machines designed since the late 1960s have included special instructions for that purpose. The call stack
10947-420: The program instructions into memory from a punched paper tape . Each subroutine could then be provided by a separate piece of tape, loaded or spliced before or after the main program (or "mainline"); and the same subroutine tape could then be used by many different programs. A similar approach was used in computers that loaded program instructions from punched cards . The name subroutine library originally meant
11070-476: The programmer can try to skip some user interaction from the original problem description and check if the remaining actions are sufficient for bugs to appear. Scripting and breakpointing are also part of this process. Debugging is often done with IDEs . Standalone debuggers like GDB are also used, and these often provide less of a visual environment, usually using a command line . Some text editors such as Emacs allow GDB to be invoked through them, to provide
11193-409: The public the evening of February 14, 1946, featuring demonstrations of its capabilities. Elizabeth Snyder and Betty Jean Jennings were responsible for developing the demonstration trajectory program, although Herman and Adele Goldstine took credit for it. The machine was formally dedicated the next day at the University of Pennsylvania. None of the women involved in programming the machine or creating
11316-558: The reader from standard IBM cards. The "first production run" of the new coding techniques on the Monte Carlo problem followed in April. After ENIAC's move to Aberdeen, a register panel for memory was also constructed, but it did not work. A small master control unit to turn the machine on and off was also added. The programming of the stored program for ENIAC was done by Betty Jennings, Clippinger, Adele Goldstine and others. It
11439-555: The register's contents to a private memory location or a register stack . In systems such as the HP 2100 , the JSB instruction would perform a similar task, except that the return address was stored in the memory location that was the target of the branch. Execution of the procedure would actually begin at the next memory location. In the HP 2100 assembly language, one would write, for example to call
11562-414: The return address in a stack addressed by an accumulator or index register. The later PDP-10 (1966), PDP-11 (1970) and VAX-11 (1976) lines followed suit; this feature also supports both arbitrarily deep subroutine nesting and recursive subroutines. In the very early assemblers, subroutine support was limited. Subroutines were not explicitly separated from each other or from the main program, and indeed
11685-516: The return value. For example, a square root callable unit might be called like y = sqrt(x) . A callable unit that does not return a value is called as a stand-alone statement like print("hello") . This syntax can also be used for a callable unit that returns a value, but the return value will be ignored. Some older languages require a keyword for calls that do not consume a return value, like CALL print("hello") . Most implementations, especially in modern languages, support parameters which
11808-482: The sign of a computed result. By the end of its operation in 1956, ENIAC contained 18,000 vacuum tubes , 7,200 crystal diodes , 1,500 relays , 70,000 resistors , 10,000 capacitors , and approximately 5,000,000 hand- soldered joints. It weighed more than 30 short tons (27 t), was roughly 8 ft (2 m) tall, 3 ft (1 m) deep, and 100 ft (30 m) long, occupied 300 sq ft (28 m ) and consumed 150 kW of electricity. Input
11931-420: The source code of a subroutine could be interspersed with that of other subprograms. Some assemblers would offer predefined macros to generate the call and return sequences. By the 1960s, assemblers usually had much more sophisticated support for both inline and separately assembled subroutines that could be linked together. One of the first programming languages to support user-written subroutines and functions
12054-570: The special instructions used for procedure calls have changed greatly over the years. The earliest computers and microprocessors, such as the Manchester Baby and the RCA 1802 , did not have a single subroutine call instruction. Subroutines could be implemented, but they required programmers to use the call sequence—a series of instructions—at each call site . Subroutines were implemented in Konrad Zuse 's Z4 in 1945. In 1945, Alan M. Turing used
12177-456: The stack contains only the private data of the calls that are currently active (namely, which have been called but haven't returned yet). Because of the ways in which programs were usually assembled from libraries, it was (and still is) not uncommon to find programs that include thousands of functions, of which only a handful are active at any given moment. For such programs, the call stack mechanism could save significant amounts of memory. Indeed,
12300-481: The stored program concept was elaborated. Von Neumann wrote up an incomplete set of notes ( First Draft of a Report on the EDVAC ) which were intended to be used as an internal memorandum—describing, elaborating, and couching in formal logical language the ideas developed in the meetings. ENIAC administrator and security officer Herman Goldstine distributed copies of this First Draft to a number of government and educational institutions, spurring widespread interest in
12423-411: The term software development is used for this larger overall process – with the terms programming , implementation , and coding reserved for the writing and editing of code per se. Sometimes software development is known as software engineering , especially when it employs formal methods or follows an engineering design process . Programmable devices have existed for centuries. As early as
12546-409: The term 'compiler'. FORTRAN , the first widely used high-level language to have a functional implementation, came out in 1957, and many other languages were soon developed—in particular, COBOL aimed at commercial data processing, and Lisp for computer research. These compiled languages allow the programmer to write programs in terms that are syntactically richer, and more capable of abstracting
12669-480: The terms "bury" and "unbury" as a means of calling and returning from subroutines. In January 1947 John Mauchly presented general notes at 'A Symposium of Large Scale Digital Calculating Machinery' under the joint sponsorship of Harvard University and the Bureau of Ordnance, United States Navy. Here he discusses serial and parallel operation suggesting ...the structure of the machine need not be complicated one bit. It
12792-404: The time) to investigate the distance that neutrons would likely travel through various materials. John von Neumann and Stanislaw Ulam realized the speed of ENIAC would allow these calculations to be done much more quickly. The success of this project showed the value of Monte Carlo methods in science. A press conference was held on February 1, 1946, and the completed machine was announced to
12915-560: The various stages of formal software development are more integrated together into short cycles that take a few weeks rather than years. There are many approaches to the Software development process. Popular modeling techniques include Object-Oriented Analysis and Design ( OOAD ) and Model-Driven Architecture ( MDA ). The Unified Modeling Language ( UML ) is a notation used for both the OOAD and MDA. A similar technique used for database design
13038-402: The warm-up and cool-down periods, when the tube heaters and cathodes were under the most thermal stress. Engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days. According to an interview in 1989 with Eckert, "We had a tube fail about every two days and we could locate the problem within 15 minutes." In 1954, the longest continuous period of operation without
13161-446: Was FORTRAN II . The IBM FORTRAN II compiler was released in 1958. ALGOL 58 and other early programming languages also supported procedural programming. Even with this cumbersome approach, subroutines proved very useful. They allowed the use of the same code in many different programs. Memory was a very scarce resource on early computers, and subroutines allowed significant savings in the size of programs. Many early computers loaded
13284-761: Was about $ 487,000, equivalent to $ 6,900,000 in 2023. The conception of ENIAC began in 1941, when Friden calculators and differential analyzers were used by the United States Army Ordnance Department to compute firing tables for artillery, which was done by graduate students under John Mauchly's supervision. Mauchly began to wonder if electronics could be applied to mathematics for faster calculations. He partnered up with research associate J. Presper Eckert , as Mauchly wasn't an electronics expert, to draft an electronic computer that could work at an excellent pace. In 1942, Mauchly proposed an all-electronic calculating machine that could help
13407-408: Was added to ENIAC. ENIAC used ten-position ring counters to store digits; each digit required 36 vacuum tubes, 10 of which were the dual triodes making up the flip-flops of the ring counter. Arithmetic was performed by "counting" pulses with the ring counters and generating carry pulses if the counter "wrapped around", the idea being to electronically emulate the operation of the digit wheels of
13530-564: Was designed by John Mauchly and J. Presper Eckert to calculate artillery firing tables for the United States Army 's Ballistic Research Laboratory (which later became a part of the Army Research Laboratory ). However, its first program was a study of the feasibility of the thermonuclear weapon . ENIAC was completed in 1945 and first put to work for practical purposes on December 10, 1945. ENIAC
13653-606: Was destroyed by the Allied bombing raids of Berlin in 1943. As the ten Colossus machines were part of the UK's war effort their existence remained secret until the late 1970s, although knowledge of their capabilities remained among their UK staff and invited Americans. ENIAC, by contrast, was put through its paces for the press in 1946, "and captured the world's imagination". Older histories of computing may therefore not be comprehensive in their coverage and analysis of this period. All but two of
13776-474: Was done by setting the switches. The idea has been worked out in several variants by Richard Clippinger and his group, on the one hand, and the Goldstines, on the other, and it was included in the ENIAC patent . Clippinger consulted with von Neumann on what instruction set to implement. Clippinger had thought of a three-address architecture while von Neumann proposed a one-address architecture because it
13899-428: Was first demonstrated as a stored-program computer in April 1948, running a program by Adele Goldstine for John von Neumann. This modification reduced the speed of ENIAC by a factor of 6 and eliminated the ability of parallel computation, but as it also reduced the reprogramming time to hours instead of days, it was considered well worth the loss of performance. Also analysis had shown that due to differences between
14022-506: Was formally dedicated at the University of Pennsylvania on February 15, 1946, having cost $ 487,000 (equivalent to $ 6,900,000 in 2023), and called a "Giant Brain" by the press. It had a speed on the order of one thousand times faster than that of electro-mechanical machines. ENIAC was formally accepted by the U.S. Army Ordnance Corps in July 1946. It was transferred to Aberdeen Proving Ground in Aberdeen, Maryland in 1947, where it
14145-554: Was in continuous operation until 1955. The 1948 Manchester Baby was the first machine to contain all the elements essential to a modern electronic digital computer, as it could be reprogrammed electronically to hold stored programs instead of requiring setting of switches to program as ENIAC did. ENIAC's design and construction was financed by the United States Army, Ordnance Corps, Research and Development Command, led by Major General Gladeon M. Barnes . The total cost
14268-476: Was possible from an IBM card reader and an IBM card punch was used for output. These cards could be used to produce printed output offline using an IBM accounting machine, such as the IBM 405 . While ENIAC had no system to store memory in its inception, these punch cards could be used for external memory storage. In 1953, a 100- word magnetic-core memory built by the Burroughs Corporation
14391-410: Was possible to wire the carry of one accumulator into another accumulator to perform arithmetic with double the precision, but the accumulator carry circuit timing prevented the wiring of three or more for even higher precision. ENIAC used four of the accumulators (controlled by a special multiplier unit) to perform up to 385 multiplication operations per second; five of the accumulators were controlled by
14514-526: Was programming during World War II. She and the other ENIAC programmers used the subroutines to help calculate missile trajectories. Goldstine and von Neumann wrote a paper dated 16 August 1948 discussing the use of subroutines. Some very early computers and microprocessors, such as the IBM 1620 , the Intel 4004 and Intel 8008 , and the PIC microcontrollers , have a single-instruction subroutine call that uses
14637-431: Was simpler to implement. Three digits of one accumulator (#6) were used as the program counter, another accumulator (#15) was used as the main accumulator, a third accumulator (#8) was used as the address pointer for reading data from the function tables, and most of the other accumulators (1–5, 7, 9–14, 17–19) were used for data memory. In March 1948 the converter unit was installed, which made possible programming through
14760-543: Was turned on and was in continuous operation until 11:45 p.m. on October 2, 1955, when it was retired in favor of the more efficient EDVAC and ORDVAC computers. A few months after ENIAC's unveiling in the summer of 1946, as part of "an extraordinary effort to jump-start research in the field", the Pentagon invited "the top people in electronics and mathematics from the United States and Great Britain" to
14883-588: Was undertaken by the female mathematicians who handled the bulk of the ENIAC programming: Jean Jennings , Marlyn Wescoff , Ruth Lichterman , Betty Snyder , Frances Bilas , and Kay McNulty . In 1946, the researchers resigned from the University of Pennsylvania and formed the Eckert–Mauchly Computer Corporation . ENIAC was a large, modular computer, composed of individual panels to perform different functions. Twenty of these modules were accumulators that could not only add and subtract, but hold
15006-402: Was used to calculate thermonuclear reactions using equations . The data was used to support research on building a hydrogen bomb. Related to ENIAC's role in the hydrogen bomb was its role in the Monte Carlo method becoming popular. Scientists involved in the original nuclear bomb development used massive groups of people doing huge numbers of calculations ("computers" in the terminology of
15129-484: Was viewed as a way to free men up for more skilled labor. Essentially, women were seen as meeting a need in a temporary crisis. For example, the National Advisory Committee for Aeronautics said in 1942, "It is felt that enough greater return is obtained by freeing the engineers from calculating detail to overcome any increased expenses in the computers' salaries. The engineers admit themselves that
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