- Great Painters
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- Education
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- English Dictionaries
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- Musical Notation
- Music Instruments
- Batteries
- Nanotechnology
- Cosmetics
- Diets
- Vegetarianism and Veganism
- Christmas Traditions
- Animals

- Fruits And Vegetables


  1. Adobe Reader
  2. Adware
  3. Altavista
  4. AOL
  5. Apple Macintosh
  6. Application software
  7. Arrow key
  8. Artificial Intelligence
  9. ASCII
  10. Assembly language
  11. Automatic translation
  12. Avatar
  13. Babylon
  14. Bandwidth
  15. Bit
  16. BitTorrent
  17. Black hat
  18. Blog
  19. Bluetooth
  20. Bulletin board system
  21. Byte
  22. Cache memory
  23. Celeron
  24. Central processing unit
  25. Chat room
  26. Client
  27. Command line interface
  28. Compiler
  29. Computer
  30. Computer bus
  31. Computer card
  32. Computer display
  33. Computer file
  34. Computer games
  35. Computer graphics
  36. Computer hardware
  37. Computer keyboard
  38. Computer networking
  39. Computer printer
  40. Computer program
  41. Computer programmer
  42. Computer science
  43. Computer security
  44. Computer software
  45. Computer storage
  46. Computer system
  47. Computer terminal
  48. Computer virus
  49. Computing
  50. Conference call
  51. Context menu
  52. Creative commons
  53. Creative Commons License
  54. Creative Technology
  55. Cursor
  56. Data
  57. Database
  58. Data storage device
  59. Debuggers
  60. Demo
  61. Desktop computer
  62. Digital divide
  63. Discussion groups
  64. DNS server
  65. Domain name
  66. DOS
  67. Download
  68. Download manager
  69. DVD-ROM
  70. DVD-RW
  71. E-mail
  72. E-mail spam
  73. File Transfer Protocol
  74. Firewall
  75. Firmware
  76. Flash memory
  77. Floppy disk drive
  78. GNU
  79. GNU General Public License
  80. GNU Project
  81. Google
  82. Google AdWords
  83. Google bomb
  84. Graphics
  85. Graphics card
  86. Hacker
  87. Hacker culture
  88. Hard disk
  89. High-level programming language
  90. Home computer
  91. HTML
  92. Hyperlink
  93. IBM
  94. Image processing
  95. Image scanner
  96. Instant messaging
  97. Instruction
  98. Intel
  99. Intel Core 2
  100. Interface
  101. Internet
  102. Internet bot
  103. Internet Explorer
  104. Internet protocols
  105. Internet service provider
  106. Interoperability
  107. IP addresses
  108. IPod
  109. Joystick
  110. JPEG
  111. Keyword
  112. Laptop computer
  113. Linux
  114. Linux kernel
  115. Liquid crystal display
  116. List of file formats
  117. List of Google products
  118. Local area network
  119. Logitech
  120. Machine language
  121. Mac OS X
  122. Macromedia Flash
  123. Mainframe computer
  124. Malware
  125. Media center
  126. Media player
  127. Megabyte
  128. Microsoft
  129. Microsoft Windows
  130. Microsoft Word
  131. Mirror site
  132. Modem
  133. Motherboard
  134. Mouse
  135. Mouse pad
  136. Mozilla Firefox
  137. Mp3
  138. MPEG
  139. MPEG-4
  140. Multimedia
  141. Musical Instrument Digital Interface
  142. Netscape
  143. Network card
  144. News ticker
  145. Office suite
  146. Online auction
  147. Online chat
  148. Open Directory Project
  149. Open source
  150. Open source software
  151. Opera
  152. Operating system
  153. Optical character recognition
  154. Optical disc
  155. output
  156. PageRank
  157. Password
  158. Pay-per-click
  159. PC speaker
  160. Peer-to-peer
  161. Pentium
  162. Peripheral
  163. Personal computer
  164. Personal digital assistant
  165. Phishing
  166. Pirated software
  167. Podcasting
  168. Pointing device
  169. POP3
  170. Programming language
  171. QuickTime
  172. Random access memory
  173. Routers
  174. Safari
  175. Scalability
  176. Scrollbar
  177. Scrolling
  178. Scroll wheel
  179. Search engine
  180. Security cracking
  181. Server
  182. Simple Mail Transfer Protocol
  183. Skype
  184. Social software
  185. Software bug
  186. Software cracker
  187. Software library
  188. Software utility
  189. Solaris Operating Environment
  190. Sound Blaster
  191. Soundcard
  192. Spam
  193. Spamdexing
  194. Spam in blogs
  195. Speech recognition
  196. Spoofing attack
  197. Spreadsheet
  198. Spyware
  199. Streaming media
  200. Supercomputer
  201. Tablet computer
  202. Telecommunications
  203. Text messaging
  204. Trackball
  205. Trojan horse
  206. TV card
  207. Unicode
  208. Uniform Resource Identifier
  209. Unix
  210. URL redirection
  211. USB flash drive
  212. USB port
  213. User interface
  214. Vlog
  215. Voice over IP
  216. Warez
  217. Wearable computer
  218. Web application
  219. Web banner
  220. Web browser
  221. Web crawler
  222. Web directories
  223. Web indexing
  224. Webmail
  225. Web page
  226. Website
  227. Wiki
  228. Wikipedia
  229. WIMP
  230. Windows CE
  231. Windows key
  232. Windows Media Player
  233. Windows Vista
  234. Word processor
  235. World Wide Web
  236. Worm
  237. XML
  238. X Window System
  239. Yahoo
  240. Zombie computer

This article is from:

All text is available under the terms of the GNU Free Documentation License: 

Software bug

From Wikipedia, the free encyclopedia


A software bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from behaving as intended (e.g., producing an incorrect result). Most bugs arise from mistakes and errors made by people in either a program's source code or its design, and a few are caused by compilers producing incorrect code. A program that contains a large number of bugs, and/or bugs that seriously interfere with its functionality, is said to be buggy. Reports detailing bugs in a program are commonly known as bug reports, fault reports, problem reports, trouble reports, change requests, and so forth.

Bugs can have a wide variety of effects, with varying levels of inconvenience to the user of the program. Some bugs have only a subtle effect on the program's functionality, and may thus lie undetected for a long time. More serious bugs may cause the program to crash or freeze leading to a denial of service. Others qualify as security bugs and might for example enable a malicious user to bypass access controls in order to obtain unauthorized privileges.

The results of bugs may be extremely serious. A bug in the code controlling the Therac-25 radiation therapy machine was directly responsible for some patient deaths and in 1996, the European Space Agency's US$1 billion prototype Ariane 5 rocket was destroyed less than a minute after launch, due to a bug in the on-board guidance computer program. In June 1994, a Royal Air Force Chinook crashed into the Mull of Kintyre, killing 29. This was initially dismissed as pilot error, but an investigation by Computer Weekly uncovered sufficient evidence to convince a House of Lords enquiry that it may have been caused by a software bug in the aircraft's FADEC. [2] [3]


The concept that software might contain errors dates back to 1842 in Ada Byron's notes on the analytical engine in which she speaks of the difficulty of preparing program 'cards' for Charles Babbage's Analytical engine:

Usage of the term "bug" to describe inexplicable defects has been a part of engineering jargon for many decades and predates computers and computer software; it may have originally been used in hardware engineering to describe mechanical malfunctions. For instance, Thomas Edison wrote the following words in a letter to an associate in 1878:

Problems with radar electronics during World War II were referred to as bugs (or glitches), and there is additional evidence that the usage dates back much earlier.

Photo of what is possibly the first actual bug found in a computer.
Photo of what is possibly the first actual bug found in a computer.

The invention of the term is often erroneously attributed to Grace Hopper, who publicized the cause of a malfunction in an early electromechanical computer. A typical version of the story is given by this quote:

Hopper was not actually the one who found the insect, as she readily acknowledged. And the date was September 9, 1947, not of 1945 [4] [5]. The operators who did find it (including William "Bill" Burke, later of the Naval Weapons Laboratory, Dahlgren Va. [3]), were familiar with the engineering term and, amused, kept the insect with the notation "First actual case of bug being found." Hopper loved to recount the story. [6]

While it is certain that the Mark II operators did not coin the term "bug", it has been suggested that they did coin the related term, "debug".


It can be psychologically difficult for some engineers to accept that their design contains bugs. They may hide behind euphemisms like "issues" or "unplanned/unexpected/undocumented features". This is also true of corporate software where a fix for a bug is often called "a reliability enhancement".

Bugs are a consequence of the nature of the programming task. Some bugs arise from simple oversights made when computer programmers write source code carelessly or transcribe data incorrectly. Many off-by-one errors fall into this category. Other bugs arise from unintended interactions between different parts of a computer program. This happens because computer programs are often complex, often having been programmed by several different people over a great length of time, so that programmers are unable to mentally keep track of every possible way in which different parts can interact. Many race condition bugs fall into this category.

The computer software industry has put a great deal of effort into finding methods for preventing programmers from inadvertently introducing bugs while writing software. These include:

Programming style 
Bugs are often created by typos that are not caught by the compiler. Some innovations to programming style such as indentation, clearly-distinguished variable names, vertically aligning similar blocks, and so forth, are designed to make these bugs less likely, or easier to spot. In curly bracket programming languages, it has become common for style documents to require that even where optional, curly brackets be placed after all control flow constructs. This prevents program-flow bugs which can be very time-consuming to track down, such as where a terminating semicolon is introduced at the end of the construct (a common typo); where another line is added before the first; or where the following line may be removed by the preprocessor. Other examples of using style to prevent bugs include placing constants on the left hand side in comparisons, (which causes a syntax error in the case of the common typo of replacing the comparison operator "==" with the assignment operator "="); placing a comma after even the last element of a list, and the last line in a block, where these are normally optional; etc.
Programming techniques 
Bugs often create inconsistencies in the internal data of a running program. Programs can be written to check the consistency of their own internal data while running. If an inconsistency is encountered, the program can immediately halt, so that the bug can be located and fixed. Alternatively, the program can simply inform the user, attempt to correct the inconsistency, and continue running.
Development methodologies 
There are several schemes for managing programmer activity, so that fewer bugs are produced. Many of these fall under the discipline of software engineering (which addresses software design issues as well.) For example, formal program specifications are used to state the exact behavior of programs, so that design bugs can be eliminated.
Programming language support 
Programming languages often include features which help programmers deal with bugs, such as exception handling. In addition, many recently-invented languages have deliberately excluded features which can easily lead to bugs. For example, the Java programming language does not support pointer arithmetic.


The typical bug history (GNU Classpath project data). A bug, submitted by the user, is unconfirmed. A reproduced bug is a confirmed bug. The confirmed bugs are later fixed. Bugs, belonging to other categories (unreproducible, will not be fixed, etc) are usually in the minority
The typical bug history (GNU Classpath project data). A bug, submitted by the user, is unconfirmed. A reproduced bug is a confirmed bug. The confirmed bugs are later fixed. Bugs, belonging to other categories (unreproducible, will not be fixed, etc) are usually in the minority
Main article: Debugging

Finding and fixing bugs, or "debugging", has always been a major part of computer programming. Maurice Wilkes, an early computing pioneer, described his realization in the late 1940s that much of the rest of his life would be spent finding mistakes in his own programs. As computer programs grow more complex, bugs become more common and difficult to fix. Often programmers spend more time and effort finding and fixing bugs than writing new code.

Usually, the most difficult part of debugging is locating the erroneous part of the source code. Once the mistake is found, correcting it is usually easy. Programs known as debuggers exist to help programmers locate bugs. However, even with the aid of a debugger, locating bugs is something of an art.

Typically, the first step in locating a bug is finding a way to reproduce it easily. Once the bug is reproduced, the programmer can use a debugger or some other tool to monitor the execution of the program in the faulty region, and find the point at which the program went astray. Sometimes, a bug is not a single flawed instruction, but represents an error of thinking or planning on the part of the programmer. Such logic errors require a section of the program to be overhauled or rewritten.

It is not always easy to reproduce bugs. Some bugs are triggered by inputs to the program which may be difficult for the programmer to re-create. One cause of the Therac-25 radiation machine deaths was a bug that occurred only when the machine operator very rapidly entered a treatment plan; it took days of practice to become able to do this, so the bug did not manifest in testing or when the manufacturer attempted to duplicate it. Other bugs may disappear when the program is run with a debugger; these are heisenbugs (humorously named after the Heisenberg uncertainty principle.)

Debugging is still a tedious task requiring considerable manpower. Since the 1990s, particularly following the Ariane 5 Flight 501 disaster, there has been a renewed interest in the development of effective automated aids to debugging. For instance, methods of static code analysis by abstract interpretation have already made significant achievements, while still remaining much of a work in progress.

Famous computer bugs

Space exploration

  • NASA Mariner 1 went off-course during launch, due to a missing 'bar' in its FORTRAN software (July 22, 1962).[7]
  • NASA Apollo 11 landing problem (July 20, 1969).
  • NASA Voyager 2 (January 25, 1986).
  • Phobos 1 lost (September 10, 1988).
  • ESA Ariane 5 Flight 501 self-destruction 40 seconds after takeoff (June 4, 1996).
  • NASA Mars Climate Orbiter destroyed due to incorrect orbit insertion (September 23, 1999).
  • Mars Polar Lander lost (December 3, 1999).
  • NASA Mars Rover freezes due to too many open files in flash memory (January 21, 2004).


  • The Therac-25 accidents (1985-1987), quite possibly the most serious computer-related failure ever in terms of human life (at least five died).


  • The year 2000 problem, popularly known as the "Y2K bug", spawned fears of worldwide economic collapse and an industry of consultants providing last-minute fixes.
  • The Pentium FDIV bug.

Electric power transmission

  • The 2003 North America blackout was triggered by a local outage that went undetected due to a race condition in General Electric Energy's XA/21 monitoring software.


  • AT&T long distance network crash (January 15, 1990), documented in Bruce Sterling's The Hacker Crackdown.


  • The MIM-104 Patriot bug, which resulted in the deaths of 28 Americans in Dharan, Saudi Arabia (February 25, 1991).
  • Chinook crash on Mull of Kintyre: the cause of this event remains a mystery, but strong suspicions have been raised that software problems were a contributory factor.

Computer and video games

  • The Missingno. and Glitch City bugs, found in the Pokémon series
  • The Minus world in NES version of Super Mario Brothers

Modern bugs and security holes

While people would like bugs to be fixed before a new release, it is common practice for software to be released with known, but considered non-critical, bugs. While software products contain an unknown number of unknown bugs when shipped, measurements during the testing may provide a statistically reliable estimate of the number of likely bugs remaining.

Security vulnerabilities

Also known as security holes. Many computer systems are able to be infected by viruses. Viruses exploit known vulnerabilities in the system - which may or may not be bugs. Viruses are not bugs in themselves - they are typically programs that are doing precisely what they were designed to do. However, viruses are occasionally referred to as such in the popular press.

Although all operating systems are vulnerable to viruses, most virus writers only target (write viruses for) operating systems with large userbases, such as various Windows versions, so as to maximize the virus distribution and damages caused by the virus.

Common types of computer bugs

  • Divide by zero
  • Infinite loops
  • Arithmetic overflow or underflow
  • Exceeding array bounds
  • Using an uninitialized variable
  • Accessing memory not owned (Access violation)
  • Memory leak or Handle leak
  • Stack overflow or underflow
  • Buffer overflow
  • Deadlock
  • Off by one error
  • Race hazard
  • Loss of precision in type conversion

See also

  • Glitch
  • ISO 9126, which classifies a bug as either a defect or a nonconformity
  • Workaround
  • Bug tracker
  • Bit rot
  • Anti-pattern
  • Unusual software bugs (Schroedinbug, Heisenbug, Bohr bug, and Mandelbug)


  1. ^ Edison to Puskas, 13 November 1878, Edison papers, Edison National Laboratory, U.S. National Park Service, West Orange, N.J., cited in Thomas P. Hughes, American Genesis: A History of the American Genius for Invention, Penguin Books, 1989, ISBN 0-14-009741-4, on page 75.
  2. ^ Danis, Sharron Ann: "Rear Admiral Grace Murray Hopper"[1]
  3. ^ IEEE Annals of the History of Computing, Vol 22 Issue 1, 2000

External links

  • Collection of Software Bugs (Thomas Huckle, TU München)
  • Computer-Related Incidents with Commercial Aircraft (Peter B. Ladkin et al., Universität Bielefeld)
  • An Investigation of the Therac-25 Accidents (Nancy Leveson, University of Washington and Clark S. Turner, University of California at Irvine)
  • Fatal Dose: Radiation Deaths linked to AECL Computer Errors (Barbara Wade Rose, Canadian Coalition for Nuclear Responsibility)
  • Software Horror Stories (Nachum Dershowitz)
  • Software Does Not Fail (Paul Niquette]
  • Picture of the "first computer bug" The error of this term is elaborated above. (Naval Historical Center)
  • Page from 1947 log book with "first actual case of bug being found" (moth) (National Museum of American History)
  • The First Computer Bug! An email from 1981 about Adm. Hopper's bug
  • How to Report Bugs Effectively (Simon G. Tatham)
  • Bug Tracking Basics: A beginner’s guide to reporting and tracking defects (Mitch Allen)
  • History's Worst Software Bugs
  • Bug Isolation Project - This project is to track bugs of popular open source software. Everyone can participate if he/she has Fedora Core 5 installed.
  • Demonstration of a bug in Google Maps.
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