The process of developing software involves several stages. The stages includesoftware design,programming,testing,release, andmaintenance.Software quality assurance andsecurity are critical aspects of software development, asbugs andsecurity vulnerabilities can lead to system failures and security breaches. Additionally, legal issues such as software licenses and intellectual property rights play a significant role in the distribution of software products.
Theintegrated circuit is an essential invention to produce modern software systems.[2]
The first use of the wordsoftware to describe computer programs is credited to mathematicianJohn Wilder Tukey in 1958.[3]The first programmable computers, which appeared at the end of the 1940s,[4] were programmed inmachine language. Machine language is difficult to debug and notportable across different computers.[5] Initially, hardware resources were more expensive thanhuman resources.[6] As programs became complex,programmer productivity became the bottleneck. The introduction ofhigh-level programming languages in 1958hid the details of the hardware and expressed the underlyingalgorithms into the code .[7][8] Early languages includeFortran,Lisp, andCOBOL.[8]
Allocating resources between different applications, deciding when they will receivecentral processing unit (CPU) time or space inmemory.[10]
Providing an interface that abstracts the details of accessinghardware details (like physical memory) to make things easier for programmers.[10][11]
Offering common services, such as an interface for accessing network and disk devices. This enables an application to be run on different hardware without needing to be rewritten.[12]
Application software runs on top of the operating system and uses the computer's resources to perform a task.[13] There are many different types of application software because the range of tasks that can be performed with modern computers is so large.[14] Applications account for most software[15] and require theenvironment provided by an operating system, and often other applications, in order to function.[16]
Software can also be categorized by how it isdeployed. Traditional applications are purchased with a perpetuallicense for a specific version of the software, downloaded, and run on hardware belonging to the purchaser.[17] The rise ofthe Internet andcloud computing enabled a new model,software as a service (SaaS),[18] in which the provider hosts the software (usually built on top of rentedinfrastructure orplatforms)[19] and provides the use of the software to customers, often in exchange for asubscription fee.[17] By 2023, SaaS products—which are usually delivered via aweb application—had become the primary method that companies deliver applications.[20]
Software companies aim to deliver a high-quality product on time and under budget. A challenge is thatsoftware development effort estimation is often inaccurate.[21]Software development begins by conceiving the project, evaluating its feasibility, analyzing the business requirements, and making asoftware design.[22][23] Most software projects speed up their development byreusing or incorporating existing software, either in the form ofcommercial off-the-shelf (COTS) oropen-source software.[24][25]Software quality assurance is typically a combination of manualcode review by other engineers[26] and automatedsoftware testing. Due to time constraints, testing cannot cover all aspects of the software's intended functionality, so developers often focus on the most critical functionality.[27]Formal methods are used in some safety-critical systems to prove the correctness of code,[28] whileuser acceptance testing helps to ensure that the product meets customer expectations.[29] There are a variety ofsoftware development methodologies, which vary from completing all steps in order to concurrent and iterative models.[30] Software development is driven byrequirements taken from prospective users, as opposed to maintenance, which is driven by events such as a change request.[31]
Frequently, software isreleased in an incomplete state when the development team runs out of time or funding.[32] Despitetesting andquality assurance, virtually all software containsbugs where the system does not work as intended. Post-releasesoftware maintenance is necessary to remediate these bugs when they are found and keep the software working as the environment changes over time.[33] New features are often added after the release. Over time, the level of maintenance becomes increasingly restricted before being cut off entirely when the product is withdrawn from the market.[34] As softwareages, it becomes known aslegacy software and can remain in use for decades, even if there is no one left who knows how to fix it.[35] Over the lifetime of the product, software maintenance is estimated to comprise 75 percent or more of the total development cost.[36][37]
Software quality is defined as meeting the stated requirements as well as customer expectations.[40] Quality is an overarching term that can refer to a code's correct and efficient behavior, its reusability andportability, or the ease of modification.[41] It is usually more cost-effective to build quality into the product from the beginning rather than try to add it later in the development process.[42] Higher quality code will reduce lifetime cost to both suppliers and customers as it is more reliable andeasier to maintain.[43][44] Software failures insafety-critical systems can be very serious including death.[43] By some estimates, the cost of poor quality software can be as high as 20 to 40 percent of sales.[45] Despite developers' goal of delivering a product that works entirely as intended, virtually all software contains bugs.[46]
The rise of the Internet also greatly increased the need forcomputer security as it enabled malicious actors to conductcyberattacks remotely.[47][48] If a bug creates a security risk, it is called avulnerability.[49][50]Software patches are often released to fix identified vulnerabilities, but those that remain unknown (zero days) as well as those that have not been patched are still liable for exploitation.[51] Vulnerabilities vary in their ability to beexploited by malicious actors,[49] and the actual risk is dependent on the nature of the vulnerability as well as the value of the surrounding system.[52] Although some vulnerabilities can only be used fordenial of service attacks that compromise a system's availability, others allow the attacker toinject and run their own code (calledmalware), without the user being aware of it.[49] To thwart cyberattacks, all software in the system must be designed to withstand and recover from external attack.[48] Despite efforts to ensure security, a significant fraction of computers are infected with malware.[53]
Programming languages are the format in which software is written. Since the 1950s, thousands of different programming languages have been invented; some have been in use for decades, while others have fallen into disuse.[54] Some definitions classifymachine code—the exact instructions directly implemented by the hardware—andassembly language—a more human-readable alternative to machine code whose statements can be translated one-to-one into machine code—as programming languages.[55] Programs written in thehigh-level programming languages used to create software share a few main characteristics: knowledge of machine code is not necessary to write them, they can beported to other computer systems, and they are more concise and human-readable than machine code.[56] They must be both human-readable and capable of being translated into unambiguous instructions for computer hardware.[57]
Compilation, interpretation, and execution
The invention of high-level programming languages was simultaneous with thecompilers needed to translate them automatically into machine code.[58] Most programs do not contain all the resources needed to run them and rely on externallibraries. Part of the compiler's function is to link these files in such a way that the program can be executed by the hardware. Once compiled, the program can be saved as anobject file and theloader (part of the operating system) can take this saved file andexecute it as aprocess on the computer hardware.[59] Some programming languages use aninterpreter instead of a compiler. An interpreter converts the program into machine code atrun time, which makes them 10 to 100 times slower than compiled programming languages.[60][61]
Software is often released with the knowledge that it is incomplete or contains bugs. Purchasers knowingly buy it in this state, which has led to a legal regime whereliability for software products is significantly curtailed compared to other products.[62]
Since the mid-1970s, software and its source code have been protected bycopyright law that vests the owner with the exclusive right to copy the code. The underlying ideas or algorithms are not protected by copyright law, but are sometimes treated as atrade secret and concealed by such methods asnon-disclosure agreements.[63] Asoftware copyright is often owned by the person or company that financed or made the software (depending on their contracts with employees orcontractors who helped to write it).[64] Some software is in thepublic domain and has no restrictions on who can use it, copy or share it, or modify it; a notable example is software written by theUnited States Government.Free and open-source software also allow free use, sharing, and modification, perhaps with a few specified conditions.[64] The use of some software is governed by an agreement (software license) written by the copyright holder and imposed on the user.Proprietary software is usually sold under a restrictive license that limits its use and sharing.[65] Some free software licenses require that modified versions must be released under the same license, which prevents the software from being soldor distributed under proprietary restrictions.[66]
Patents give an inventor an exclusive, time-limited license for a novel product or process.[67] Ideas about what software could accomplish are not protected by law and concrete implementations are instead covered bycopyright law. In some countries, a requirement for the claimed invention to have an effect on the physical world may also be part of the requirements for a software patent to be held valid.[68]Software patents have beenhistorically controversial. Before the 1998 caseState Street Bank & Trust Co. v. Signature Financial Group, Inc., software patents were generally not recognized in the United States. In that case, theSupreme Court decided that business processes could be patented.[69] Patent applications are complex and costly, and lawsuits involving patents can drive up the cost of products.[70] Unlike copyrights, patents generally only apply in the jurisdiction where they were issued.[71]
^Stair, Ralph M. (2003).Principles of Information Systems, Sixth Edition. Thomson. p. 16.ISBN0-619-06489-7.Software consists of computer programs that govern the operation of the computer.
^Gerardo Con Díaz, "The Text in the Machine: American Copyright Law and the Many Natures of Software, 1974–1978",Technology and Culture 57 (October 2016), 753–79.
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