Crash (computing) - AbsoluteAstronomy.com

A crash in computing

Computing

Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...

is a condition where a computer or a program, either an application

Application software

Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...

or part of the operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

, ceases to function properly, often exiting after encountering errors. Often the offending program may appear to freeze or hang

Hang (computing)

In computing, a hang or freeze occurs when either a single computer program, or the whole system ceases to respond to inputs. In the most commonly encountered scenario, a workstation with a graphical user interface, all windows belonging to the frozen program become static, and though the mouse...

until a crash reporting service

Crash reporter

A crash reporter is an application whose function is to report crash data to a third party, usually to the party responsible for the crashed program. Crash reports often include data such as stack traces, type of crash, and version of software...

documents details of the crash. If the program is a critical part of the operating system kernel, the entire computer may crash. This is different from a hang or freeze where the application or OS continues to run without obvious response to input.

Many crashes are the result of the execution of a single machine instruction, but the causes of this are many fold. Typical causes are when the program counter

Program counter

The program counter , commonly called the instruction pointer in Intel x86 microprocessors, and sometimes called the instruction address register, or just part of the instruction sequencer in some computers, is a processor register that indicates where the computer is in its instruction sequence...

is set to an incorrect address or a buffer overflow

Buffer overflow

In computer security and programming, a buffer overflow, or buffer overrun, is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory. This is a special case of violation of memory safety....

overwrites a portion of program code due to an earlier bug. In either case, it is quite common for the processor

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

to attempt to execute data or random memory values. Since all data values are possible but only some values are valid instructions, this often results in an illegal instruction exception. By chance such data or random values could be valid (though unplanned) instructions. One might say that the original bug that upset the program counter "caused" the crash, but the actual fault was an illegal instruction some time later. The art of debugging

Debugging

Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...

such crashes is connecting the actual cause of the crash (easily determined) with the code that set off the chain of events. This is often very far from obvious—the original bug is usually perfectly valid code from the processor's perspective.

On earlier personal computers, it was actually possible to cause hardware damage through trying to write to hardware addresses outside of the system's main memory. Occasionally, execution of arbitrary data on a system will result in a breakup of screen display. This is widely considered a severe system crash.

Etymology

The term "crash" may originate from the phrase "head crash

Head crash

A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive comes in contact with its rotating platter, resulting in permanent and usually irreparable damage to the magnetic media on the platter surface....

", which occurs when the read/write heads

Disk read-and-write head

Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...

inside a hard disk

Hard disk

A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...

physically come into contact with--"crash" into—the platter

Hard disk platter

A hard-disk platter is a component of a hard-disk drive: it is the circular disk on which the magnetic data is stored. The rigid nature of the platters in a hard drive is what gives them their name . Hard drives typically have several platters which are mounted on the same spindle...

, the magnetic data storage surface of a hard disk. A head crash is catastrophic to the drive operation, roughly analogous to the severity of a computer crash to computer software.

Application crashes

An application

Application software

typically crashes when it performs an operation which is not allowed by the operating system. The operating system then triggers an exception

Exception handling

Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of exceptions, special conditions that change the normal flow of program execution....

or signal

Signal (computing)

A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. Essentially it is an asynchronous notification sent to a process in order to notify it of an event that occurred. When a signal is sent to a process, the operating system...

in the application. Unix applications traditionally responded to the signal by dumping core

Core dump

In computing, a core dump consists of the recorded state of the working memory of a computer program at a specific time, generally when the program has terminated abnormally...

. Most Windows and Unix GUI

Gui

Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...

applications respond by displaying a dialog box (such as the one shown to the right) with the option to attach a debugger

Debugger

A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...

if one is installed. This behavior is called "crashing". Some applications attempt to recover from the error and continue execution instead of crashing.

Typical errors that result in application crashes include:

attempting to read or write memory that is not allocated for reading or writing by that application (segmentation fault
Segmentation fault
A segmentation fault , bus error or access violation is generally an attempt to access memory that the CPU cannot physically address. It occurs when the hardware notifies an operating system about a memory access violation. The OS kernel then sends a signal to the process which caused the exception...

) or x86 specific (general protection fault
General protection fault
A general protection fault in the Intel x86 and AMD x86-64 architectures, and other unrelated architectures, is a fault that can encompass several cases in which protection mechanisms within the processor architecture are violated by any of the programs that are running, either the kernel or a...

)
attempting to execute privileged or invalid instructions
attempting to perform I/O operations on hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....

devices to which it does not have permission to access
passing invalid arguments to system calls
attempting to access other system resources to which the application does not have permission to access (bus error)
attempting to execute machine instructions with bad arguments (depending on CPU architecture): divide by zero
Divide By Zero
Divide By Zero was a British video game developer. It was disestablished sometime in 1996.Divide By Zero is a BBS originally started in 1996 in Columbia SC by Keven and Eric Coots...

, operations on denorms
Denormal number
In computer science, denormal numbers or denormalized numbers fill the underflow gap around zero in floating point arithmetic: any non-zero number which is smaller than the smallest normal number is 'sub-normal'.For example, if the smallest positive 'normal' number is 1×β−n In computer...

or NaN
NaN
In computing, NaN is a value of the numeric data type representing an undefined or unrepresentable value, especially in floating-point calculations...

values, memory access to unaligned addresses, etc.

Website server crashes

The software running the server

Web server

Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....

behind a website

Website

A website, also written as Web site, web site, or simply site, is a collection of related web pages containing images, videos or other digital assets. A website is hosted on at least one web server, accessible via a network such as the Internet or a private local area network through an Internet...

may crash, rendering it inaccessible entirely or providing only an error message instead of normal content.

For example: If a site was using a SQL database (such as MySQL) for a script (such as php) and that SQL server crashed, then php would display a connection error.

Operating system crashes

An operating system crash commonly occurs when a hardware exception occurs that cannot be handled. Operating system crashes can also occur when internal sanity-checking logic within the operating system detects that the operating system has lost its internal self-consistency.

Modern multi-tasking operating systems, such as Windows NT, Linux, or Mac OS X usually remain unharmed when an application program crashes.

Etymology

Application crashes

Website server crashes

Operating system crashes

See also