computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...

, rebooting is the process by which a running

computer system A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These progr ...

is restarted, either intentionally or unintentionally. Reboots can be either a cold reboot (alternatively known as a hard reboot) in which the power to the system is physically turned off and back on again (causing an initial boot of the machine); or a warm reboot (or soft reboot) in which the system restarts while still powered up. The term restart (as a system command) is used to refer to a reboot when the

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

closes all programs and finalizes all pending input and output operations before initiating a soft reboot.

Terminology

Etymology

Early electronic computers (like the

IBM 1401 The IBM 1401 is a variable-wordlength decimal computer that was announced by IBM on October 5, 1959. The first member of the highly successful IBM 1400 series, it was aimed at replacing unit record equipment for processing data stored on pu ...

) had no operating system and little internal memory. The input was often a stack of

punch cards A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...

or via a Switch Register. On systems with cards, the computer was initiated by pressing a start button that performed a single command - "read a card". This first card then instructed the machine to read more cards that eventually loaded a user program. This process was likened to an old saying, " picking yourself up by the bootstraps", referring to a horseman who lifts himself off the ground by pulling on the straps of his boots. This set of initiating punch cards was called "bootstrap cards". Thus a cold start was called ''

booting In computing, booting is the process of starting a computer as initiated via hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so som ...

'' the computer up. If the computer

crashed "Crashed" is the third U.S. rock Single (music), single, (the fifth overall), from the band Daughtry (band), Daughtry's debut album. It was released only to U.S. rock stations on September 5, 2007. Upon its release the song got adds at those stat ...

, it was rebooted. The boot reference carried over to all subsequent types of computers.

Cold versus warm reboot

For

IBM PC compatible IBM PC compatible computers are similar to the original IBM PC, XT, and AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such computers were referred to as PC clones, IBM clones or IBM PC clones. ...

computers, a cold boot is a boot process in which the computer starts from a powerless state, in which the system performs a

power-on self-test A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on. This article mainly deals with POSTs on personal computers, but many other embed ...

(POST). Both the operating system and third-party software can initiate a cold boot; the restart command in

Windows 9x Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subs ...

initiates a cold reboot, unless Shift key is held. A warm boot'' is initiated by the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

, either as a result of the

Control-Alt-Delete Control-Alt-Delete (often abbreviated to Ctrl+Alt+Del, also known as the "three-finger salute" or "Security Keys") is a computer keyboard command on IBM PC compatible computers, invoked by pressing the Delete key while holding the Control key, C ...

key combination or directly through BIOS interrupt INT 19h. It does not perform a POST.

Malware Malware (a portmanteau for ''malicious software'') is any software intentionally designed to cause disruption to a computer, server, client, or computer network, leak private information, gain unauthorized access to information or systems, depri ...

may prevent or subvert a warm boot by intercepting the Ctrl + Alt + Delete key combination and prevent it from reaching BIOS. The

Windows NT Windows NT is a proprietary graphical operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems sc ...

family of operating systems also does the same and reserves the key combination for its own use. The

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

family of operating systems supports an alternative to warm boot; the Linux kernel has optional support for

kexec kexec, abbreviated from ''kernel execute'' and analogous to the Unix/Linux kernel call ''exec'', is a mechanism of the Linux kernel that allows booting of a new kernel from the currently running one. Essentially, kexec skips the bootloader stage ...

, a

system call In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, acc ...

which transfers execution to a new kernel and skips hardware or firmware reset. The entire process occurs independently of the system firmware. The kernel being executed does not have to be a Linux kernel. Outside the domain of IBM PC compatible computers, the types of boot may not be as clear. According to Sue Loh of

Windows CE Windows Embedded Compact, formerly Windows Embedded CE, Windows Powered and Windows CE, is an operating system subfamily developed by Microsoft as part of its Windows Embedded family of products. Unlike Windows Embedded Standard, which is base ...

Base Team, Windows CE devices support three types of boots: Warm, cold and clean. A warm boot discards program memory. A cold boot additionally discards storage memory (also known as the "object store"), while a clean boot erases ''all'' forms of memory storage from the device. However, since these areas do not exist on all Windows CE devices, users are only concerned with two forms of reboot: one that resets the volatile memory and one that wipes the device clean and restores factory settings. For example, for a

Windows Mobile 5.0 Windows Mobile 5.0, originally codenamed "Magneto",De Herrera, Chris pocketpcfaq.com. Retrieved September 6, 2007. was released at Microsoft's Mobile and Embedded Developers Conference 2005 in Las Vegas, May 9–12, 2005. Microsoft offered mains ...

device, the former is a cold boot and the latter is a clean boot.

Hard reboot

A hard reboot means that the system is not shut down in an orderly manner, skipping file system synchronisation and other activities that would occur on an orderly shutdown. This can be achieved by either applying a reset, by cycling power, by issuing the command in most

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

systems, or by triggering a

kernel panic A kernel panic (sometimes abbreviated as KP) is a safety measure taken by an operating system's kernel upon detecting an internal fatal error in which either it is unable to safely recover or continuing to run the system would have a higher ...

. Hard reboots are used in the

cold boot attack In computer security, a cold boot attack (or to a lesser extent, a platform reset attack) is a type of side channel attack in which an attacker with physical access to a computer performs a memory dump of a computer's random-access memory (RAM) by ...

Restart

The term "restart" is used by the

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

and

families of operating systems to denote an operating system-assisted reboot. In a restart, the operating system ensures that all pending I/O operations are gracefully ended before commencing a reboot.

Causes

Deliberate

Users may deliberately initiate a reboot. Rationale for such action may include: *Troubleshooting: Rebooting may be used by users, support staff or system administrators as a technique to work around bugs in software, for example

memory leak In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in a way that Computer memory, memory which is no longer needed is not released. A memory leak may also happe ...

s or processes that hog resources to the detriment of the overall system, or to terminate

malware Malware (a portmanteau for ''malicious software'') is any software intentionally designed to cause disruption to a computer, server, client, or computer network, leak private information, gain unauthorized access to information or systems, depri ...

. While this approach does not address the root cause of the issue, resetting a system back to a good, known state may allow it to be used again for some period until the issue next occurs. *Switching operating systems: On a

multi-boot Multi-booting is the act of installing multiple operating systems on a single computer, and being able to choose which one to boot. The term dual-booting refers to the common configuration of specifically two operating systems. Multi-booting m ...

system without a

hypervisor A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is calle ...

, a reboot is required to switch between installed operating systems. *Offensive: As stated earlier, components lose power during a cold reboot; therefore, components such as

RAM Ram, ram, or RAM may refer to: Animals * A male sheep * Ram cichlid, a freshwater tropical fish People * Ram (given name) * Ram (surname) * Ram (director) (Ramsubramaniam), an Indian Tamil film director * RAM (musician) (born 1974), Dutch * ...

that require power lose the data they hold. However, in a

, special configurations may allow for part of the system state, like a RAM disk, to be preserved through the reboot. The means of performing a deliberate reboot also vary and may include: *Manual, hardware-based: A power switch or

reset button In electronics and technology, a reset button is a button that can reset a device. On video game consoles, the reset button restarts the game, forfeiting the player's unsaved progress. On personal computers,On IBM mainframes reset neither cl ...

can cause the system to reboot. Doing so, however, may cause the loss of all unsaved data. *Manual, software-based: Computer software and operating system can trigger a reboot as well; more specifically,

operating systems are outfitted with a restart command that closes open programs and eliminates data loss due to reboot. *Automated: Software can be scheduled to run at a certain time and date; therefore, it is possible to schedule a reboot.

Power failure

Unexpected loss of power for any reason (including

power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricit ...

power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...

failure or depletion of

battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

on a mobile device) forces the system user to perform a cold boot once the power is restored. Some

es have an option to automatically boot the system after a power failure. An

uninterruptible power supply An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system ...

(UPS), backup battery or redundant power supply can prevent such circumstances.

Random reboot

"Random reboot" is a non-technical term referring to an unintended (and often undesired) reboot following a system crash, whose root cause may not immediately be evident to the user. Such crashes may occur due to a multitude of software and hardware problems, such as

triple fault On the x86 computer architecture, a triple fault is a special kind of exception generated by the CPU when an exception occurs while the CPU is trying to invoke the double fault exception handler, which itself handles exceptions occurring while ...

s. They are generally symptomatic of an error in ring 0 that is not trapped by an error handler in an operating system or a hardware-triggered

non-maskable interrupt In computing, a non-maskable interrupt (NMI) is a hardware interrupt that standard interrupt-masking techniques in the system cannot ignore. It typically occurs to signal attention for non-recoverable hardware errors. Some NMIs may be masked, but ...

. Systems may be configured to reboot automatically after a power failure, or a

fatal system error A fatal system error (also known as a system crash, stop error, kernel error, or bug check) occurs when an operating system halts because it has reached a condition where it can no longer operate safely (''i.e.'' where critical data could be l ...

. The method by which this is done varies depending on whether the reboot can be handled via software or must be handled at the firmware or hardware level. Operating systems in the

family (from

Windows NT 3.1 Windows NT 3.1 is the first major release of the Windows NT operating system developed by Microsoft, released on July 27, 1993. At the time of Windows NT's release, Microsoft's Windows 3.1 desktop environment had established brand recognition ...

through

Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on July 22, 2009, and became generally available on October 22, 2009. It is the successor to Windows Vista, released nearly ...

) have an option to modify the behavior of the error handler so that a computer immediately restarts rather than displaying a Blue Screen of Death (BSOD) error message. This option is enabled by default in some editions.

Hibernation

The introduction of

advanced power management Advanced power management (APM) is an API developed by Intel and Microsoft and released in 1992 which enables an operating system running an IBM-compatible personal computer to work with the BIOS (part of the computer's firmware) to achieve power m ...

allowed operating systems greater control of hardware power management features. With

Advanced Configuration and Power Interface Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto c ...

(ACPI), newer operating systems are able to manage different power states and thereby sleep and/or

hibernate Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...

. While hibernation also involves turning a system off then subsequently back on again, the operating system does not start from scratch, thereby differentiating this process from rebooting.

Simulated reboot

A reboot may be simulated by software running on an operating system. For example: the Sysinternals BlueScreen utility, which is used for pranking; or some modes of the

XScreenSaver XScreenSaver is a free and open-source collection of 240+ screensavers for Unix, macOS, iOS and Android operating systems. It was created by Jamie Zawinski in 1992 and is still maintained by him, with new releases coming out several times ...

"hack", for entertainment (albeit possibly concerning at first glance). Malware may also simulate a reboot, and thereby deceive a computer user for some nefarious purpose.

Microsoft App-V Microsoft Application Virtualization (also known as App-V; formerly Softricity SoftGrid) is an application virtualization and application streaming solution from Microsoft. It was originally developed by Softricity, a company based in Boston, Mas ...

sequencing tool captures all the file system operations of an installer in order to create a virtualized software package for users. As part of the sequencing process, it will detect when an installer requires a reboot, interrupt the triggered reboot, and instead simulate the required reboot by restarting services and loading/unloading libraries.

Windows deviations and labeling criticism

Windows 8 Windows 8 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on August 1, 2012; it was subsequently made available for downl ...

& 10 enable (by default) a

hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...

-like "Fast Startup" (a.k.a. "Fast Boot") which can cause problems (including confusion) for users accustomed to turning off computers to (cold) reboot them.

References

{{Reflist, 2, refs = {{Cite book , url=https://books.google.com/books?id=WtE9GN1hhvAC , title=A+ Exam Cram 2 (Exam Cram 220-221, Exam Cram 220-222) , publisher=Que Publishing , year=2002 , first1=James G. , last1=Jones , first2=Craig , last2=Landes , first3=Ed , last3=Tittel , isbn=9780789728678 , pages=379–380, 509 {{Cite book , url=https://books.google.com/books?id=KHCRkX5d-gAC , title=Absolute Beginner's Guide to A+ Certification , publisher=Que Publishing , year= 2004 , first1=Mark Edward , last1=Soper , isbn=9780789730626 , page=188 {{Cite book , url=https://books.google.com/books?id=u7oN-5y7nGsC , title=Using MS-DOS 6.22 , publisher=Que Publishing , year=2002 , first1=Jim , last1=Cooper , isbn=9780789725738 , pages=24, 960, 964 {{Cite book , title=Microsoft Encyclopedia of Networking , edition=2nd , first1=Mitch , last1=Tulloch , first2=Ingrid , last2=Tulloch , publisher=Microsoft Press , isbn=0-7356-1378-8 , year=2002 , page=172 {{Cite web , url=http://support.microsoft.com/kb/102228 , title=Hardware Troubleshooting: Cold Booting Versus Warm Booting , work=Support , publisher=Microsoft , date=7 July 2005 , archive-url=https://web.archive.org/web/20150221095215/http://support.microsoft.com/kb/102228 , archive-date=21 February 2015 {{Cite book , chapter-url=https://books.google.com/books?id=GKDtVYJ0wesC&pg=PA50 , title=Malicious Mobile Code: Virus Protection for Windows , publisher=O'Reilly Media , first=Roger , last=Grimes , date=1 June 2001 , chapter=2 , isbn=9781565926820 , page=50 {{Cite book , url=https://books.google.com/books?id=GDwIOT1FiwkC , title=Enhanced Discovering Computers, Complete: Your Interactive Guide to the Digital World, 2013 Edition , publisher=Cengage Learning , year=2012 , first1=Gary B. , last1=Shelly , first2=Misty E. , last2=Vermaat , isbn=9781133598312 , page=400 Booting BIOS Computer errors Computer jargon