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Encyclopedia > Boot ROM

In computing, booting (booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. A boot sequence is the set of operations the computer performs when it is switched on that loads an operating system. Memory (Random Access Memory) Look up computing in Wiktionary, the free dictionary. ... In computing, Bootstrapping refers to a process where a simple system activates another more complicated system that serves the same purpose. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ... To meet Wikipedias quality standards, this article may require cleanup. ...

Contents

Boot loader

Most computer systems can only execute code found in the memory (ROM or RAM). Modern operating systems are stored on hard disks, or occasionally on LiveCDs, USB flash drives, or other non-volatile storage devices. When a computer is first powered on, it doesn't have an operating system in memory. The computer's hardware alone cannot perform complex actions such as loading a program from disk, so an apparent paradox exists: to load the operating system into memory, one appears to need to have an operating system already loaded. A BlueGene supercomputer cabinet. ... Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... Typical hard drives of the mid-1990s. ... Gnoppix 0. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ... Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. ... Look up paradox in Wiktionary, the free dictionary. ...


The solution is to use a special small program, called a bootstrap loader, bootstrap or boot loader. This program's only job is to load other software for the operating system to start. Often, multiple-stage boot loaders are used, in which several small programs of increasing complexity summon each other, until the last of them loads the operating system. The name bootstrap loader comes from the image of one pulling oneself up by one's bootstraps (see bootstrapping). It derives from the very earliest days of computers and is possibly one of the oldest pieces of computer terminology in common use. A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ... In computing, Bootstrapping refers to a process where a simple system activates another more complicated system that serves the same purpose. ...


Early programmable computers had a row of toggle switches on the front panel to allow the operator to manually enter the binary boot instructions into memory before transferring control to the CPU. The boot loader would then read the operating system in from an outside storage medium such as paper tape, punched card, or an old fixed head disk drive. A toggle switch is a generic class of electric switch that uses a mechanical lever, handle or rocking mechanism to actuate it. ... The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ... Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ... A roll of punched tape Punched tape is an old-fashioned form of data storage, consisting of a long strip of paper in which holes are punched to store data. ... A CTR census machine, utilizing a punched card system. ... Disk Drive is the afternoon show on CBC Radio Two. ...


Pseudo-assembly code for the bootloader might be as simple as the following eight instructions: Pseudo is a prefix of Greek origin. ... See the terminology section, below, regarding inconsistent use of the terms assembly and assembler. ...

 0: set the P register to 8 1: check paper tape reader ready 2: if not ready, jump to 1 3: read a byte from paper tape reader to accumulator 4: if end of tape, jump to 8 5: store accumulator to address in P register 6: increment the P register 7: jump to 1 

A related example is based on a loader for a 1970's Nicolet Instrument Corporation minicomputer. Note that the bytes of the second-stage loader are read from paper tape in reverse order. Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). ...

 0: set the P register to 106 1: check paper tape reader ready 2: if not ready, jump to 1 3: read a byte from paper tape reader to accumulator 4: store accumulator to address in P register 5: decrement the P register 6: jump to 1 

The length of the second stage loader is such that the final byte overwrites location 6. After the instruction in location 5 executes, location 6 starts the second stage loader executing. The second stage loader then waits for the much longer tape containing the operating system to be placed in the tape reader. The difference between the boot loader and second stage loader is the addition of checking code to trap paper tape read errors, a frequent occurrence with the hardware of the time, which in this case was an ASR-33 teletype. ASR33 Teletype Introduced about 1963, Teletype Corporations ASR33 was a very popular model of teleprinter. ... A teleprinter (teletypewriter, teletype or TTY) is a now largely obsolete electro-mechanical typewriter which can be used to communicate typed messages from point to point through a simple electrical communications channel, often just a pair of wires. ...


In modern computers the bootstrapping process begins with the CPU executing software contained in ROM (for example, the BIOS of an IBM PC) at a predefined address (the CPU is designed to execute this software after reset without outside help). This software contains rudimentary functionality to search for devices eligible to participate in booting, and load a small program from a special section (most commonly the boot sector) of the most promising device. It is usually possible to configure the BIOS so that only a certain device can be booted from and/or to give priority to some devices over others (a CD or DVD drive is usually given priority over a hard disk, for instance). Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ... This article or section does not adequately cite its references or sources. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... A boot sector is a sector of a hard disc, floppy disc, or similar data storage device that contains code for bootstrapping programs (usually, but not necessarily, operating systems) stored in other parts of the disc. ...


Boot loaders may face peculiar constraints, especially in size; for instance, on the IBM PC and compatibles, the first stage of boot loaders located on hard drives must fit into the first 446 bytes of the Master Boot Record, in order to leave room for the 64-byte partition table and the 2-byte 0xAA55 'signature', which the BIOS requires for a proper boot loader. This article refers to the unit of binary information. ... A Master Boot Record (MBR), or partition sector, is the 512-byte boot sector that is the first sector (Sector 0) of a partitioned data storage device such as a hard disk. ... In general, a partition is a splitting into parts. ...


Some operating systems, most notably pre-1995 Macintosh systems from Apple Computer, are so closely interwoven with their hardware that it is impossible to natively boot an operating system other than the standard one. A common solution in such situations is to design a bootloader that works as a program belonging to the standard OS that hijacks the system and loads the alternative OS. This technique was used by Apple for its A/UX Unix implementation and copied by various freeware operating systems and BeOS Personal Edition 5. The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac. The Macintosh or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple Computer. ... Apple Inc. ... A/UX (from Apple Unix) is Apple Computers implementation of the Unix operating system for some of their Macintosh computers. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®) is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... BeOS is an operating system for personal computers which began development by Be Inc. ...


Second-stage boot loader

The small program is most often not itself an operating system, but only a second-stage boot loader, such as NTLDR, LILO or GRUB. It will then be able to load the operating system properly, and finally transfer execution to it. The system will initialize itself, and may load device drivers and other programs that are needed for the normal operation of the OS. An NTLDR boot menu. ... LILO (LInux LOader) is a boot loader for Linux. ... This article or section does not cite any references or sources. ... Windows XP loading drivers during a Safe Mode bootup A device driver, or a software driver is a specific type of computer software, typically developed to allow interaction with hardware devices. ...


The boot process is considered complete when the computer is ready to interact with the user or the operating system is capable of running ordinary applications. Typical modern PCs boot in about a minute (of which about 15 seconds are taken by a Power-on self test (POST) and the preliminary boot loaders, and the rest by loading the operating system), while large servers may take several minutes to boot and to start all services. To ensure high availability, they bring up some services before others. An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ... The Altair 8800 was among the first microcomputers to be affordable by an individual, although it initially lacked peripherals and memory. ... Power-on Self Test (POST) is the common term for a computers pre-boot sequence. ...


Most embedded systems must boot immediately. For example, waiting a minute for a digital television to come up is not acceptable. Therefore they have their complete operating system in ROM or flash memory, so it can be executed directly. It has been suggested that Embedded System Design in an FPGA be merged into this article or section. ... A USB flash drive. ...


Flash boot loader

Embedded systems especially in automotive applications rely heavily on Flash Bootloaders to ensure that the ECU (Electronic Control Unit) is programmable either in production or in service. A Flash Bootloader resides in Flash memory, and is always the first application to run after a reset. The Flash bootloader decides whether an application is ready and thereby either stays in the ECU or jumps to the application to start execution. The benefit of having a Flash Bootloader on an ECU is mainly to allow erasing and programming new applications on a single ECU in case of application updates, a recall, or changing a configuration by downloading new calibration files. The most popular Flash Bootloaders are CAN based, i.e. use the Control Area Network protocol to download data to an ECU. These bootloaders use a Diagnostics protocol to communicate and download to an ECU. In automotive electronics, an electronic control unit (ECU) is an embedded microcomputer that controls one or more of the electrical subsystems in a vehicle. ... Controller Area Network (CAN) is a broadcast, differential serial bus standard, originally developed in the 1980s by Robert Bosch GmbH, for connecting electronic control units (ECUs). ... ...


Network booting

Main article: Network booting

Most computers are also capable of booting over a computer network. In this scenario, the operating system is stored on the disk of a server, and certain parts of it are transferred to the client using a simple protocol such as the Trivial File Transfer Protocol. After these parts have been transferred, the operating system then takes over control of the booting process. Network booting is the process of booting a computer from a network rather than a local drive. ... “Computer Networks” redirects here. ... This article or section does not cite any references or sources. ... Trivial File Transfer Protocol (TFTP) is a very simple file transfer protocol, with the functionality of a very basic form of FTP; it was first defined in 1980. ...


Boot devices

A boot device is any device that must be initialized prior to loading the operating system. This includes the primary input device (keyboard), the primary output device (display), and the initial program load device (floppy drive, hard drive, CD-ROM, USB flash drive, etc.). // Telegraph key (~20 WPM Morse code) Vibroplex (30–80 WPM Morse) See also: Chinese input methods for computers, Telecommunications devices for the deaf, Txt speak Keyboard Touchpad Joystick Gamepad (or joypad) Power Pad Analog stick Yoke (aircraft) Image scanner 3D scanner Digital camera Webcam Assistive Technology Brain-computer interface Input... A computer keyboard is a peripheral partially modeled after the typewriter keyboard. ... Nixie tubes, LED-display and VF-display A display device, also known as an information display is a device for visual or tactile presentation of images (including text) acquired, stored, or transmitted in various forms. ... Initial program load or IPL (sometimes pronounced as ) is a term for the start-up phase of a computers operation. ... A floppy disk is a data storage device that comprises a circular piece of thin, flexible (hence floppy) magnetic storage medium encased in a square or rectangular plastic wallet. ... Typical hard drives of the mid-1990s. ... The CD-ROM (an abbreviation for Compact Disc Read-Only Memory (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. ... A USB flash drive, shown with a 24 mm U.S. quarter coin for scale. ...


In a modern BIOS, the user can select one of several interfaces from which to boot. These include: hard disk, floppy, SCSI, CDROM, Zip, LS-120, a network interface card using PXE, or USB (USB-FDD, USB-ZIP, USB-CDROM, USB-HDD). This article or section does not adequately cite its references or sources. ... Typical hard drives of the mid-1990s. ... This article or section does not adequately cite its references or sources. ... This article or section does not cite any references or sources. ... The CD-ROM (an abbreviation for Compact Disc Read-Only Memory (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. ... Iomega ZIP-100 Drive Logo An internal Zip drive. ... Also known as the LS-120 and the later variant LS-240, the SuperDisk was introduced by 3Ms storage products group (later known as Imation) circa 1997 as a high-speed, high-capacity alternative to the 3. ... The Preboot Execution Environment (PXE, aka Pre-Execution Environment, or pixie) is an environment to bootstrap computers using a network interface card independently of available data storage devices (like hard disks) or installed operating systems. ... Universal Serial Bus (USB) is a serial bus standard to interface devices. ...


For example, one can install Microsoft Windows on the first hard disk and Linux on the second. By changing the BIOS boot device, the user can select the operating system to load. Microsoft Windows is the name of several families of proprietary software operating systems by Microsoft. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ...


Boot sequence on standard PC (IBM-PC compatible)

A PC going through its boot sequence

Upon starting, a personal computer's x86 CPU runs the instruction located at the memory location F000:FFF0 (on 286s and 386SXs, the base of the code segment is actually 0xFF0000 and on 386s it is 0xFFFF0000) of the BIOS. This memory location is close to the end of system memory. It contains a jump instruction that transfers execution to the location of the BIOS start-up program. This program runs a Power-on self test (POST) to check that devices the computer will rely on are functioning; it also initializes these devices. Then, the BIOS goes through a preconfigured list of devices until it finds one that is bootable. On real IBM PCs and derivatives made by IBM, if it finds no such device, control is transferred to IBM Cassette BASIC. On other IBM PC compatibles, an error message is generated and the boot process stops. If the BIOS finds a bootable device, it loads and executes its boot sector. In the case of a hard drive, this is referred to as the master boot record (MBR) and is often not operating system specific. Usually, the MBR code checks the partition table for an active partition. If one is found, the MBR code loads that partition's boot sector and executes it. The boot sector is often operating system specific, however in most operating systems its main function is to load and execute a kernel, which continues startup. If there is no active partition or the active partition's boot sector is invalid, the MBR may load a secondary boot loader and pass control to it and this secondary boot loader will select a partition (often via user input) and load its boot sector, which usually loads the corresponding operating system Kernel. Newer systems that have EFI-compliant firmware can boot from that to either MBR or GPT drives and do not use the standard MBR boot loader. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ... This article or section does not adequately cite its references or sources. ... Power-on Self Test (POST) is the common term for a computers pre-boot sequence. ... IBM Cassette BASIC was a version of the Microsoft BASIC programming language licensed by IBM for the IBM PC. It was included in the BIOS ROM of the original IBM PC. Cassette BASIC provided the default user interface if there was no floppy disk drive installed, or if the boot... This article or section does not cite its references or sources. ... A boot sector is a sector of a hard disc, floppy disc, or similar data storage device that contains code for bootstrapping programs (usually, but not necessarily, operating systems) stored in other parts of the disc. ... A Master Boot Record (MBR), or partition sector, is the 512-byte boot sector that is the first sector (Sector 0) of a partitioned data storage device such as a hard disk. ... A partition in the IBM PC architecture, is a part of a hard disk that can have an independent file system. ... A boot sector is a sector of a hard disc, floppy disc, or similar data storage device that contains code for bootstrapping programs (usually, but not necessarily, operating systems) stored in other parts of the disc. ... A kernel connects the application software to the hardware of a computer. ... The workings of the Extensible Firmware Interface The Extensible Firmware Interface (EFI) is a software interface between an operating system and platform firmware. ...


Other kinds of boot sequence

Some other processors have other kinds of boot modes; most digital signal processors have the following boot modes: A digital signal processor (DSP) is a specialized microprocessor designed specifically for digital signal processing, generally in real-time. ...

  • Serial mode boot
  • Parallel mode boot
  • HPI boot

Initial Program Load

In IBM mainframe systems, the boot process is known as IPL (Initial Program Load) The term was coined by IBM for the design of the System/360 and continues to be used in those environments today[1]. In systems that share the System/360 heritage—and in some that have been inspired by it, including smaller systems such as the IBM 1130—IPL is a hardware function, not a program run on the system itself. A predefined I/O channel command is initiated to a selected device directly, causing a startup program to be loaded without the assistance of a pre-defined bootstrap routine. The exact same procedure is used to boot from any device, including disk drives, tape drives, or even card readers, in a device-independent manner. System/360 Model 65 operators console, with register value lamps and toggle switches (middle of picture) and emergency pull switch (upper right). ... Operator loading a 2315 disk cartridge into the IBM 1130 computer. ... DDS tape drive. ... A card reader is a device used for communication with a smart card or a flash memory card. ...


The System/360 IPL function reads 24 bytes from an operator-specified or pre-configured device into memory starting at location zero. The second and third groups of eight bytes are treated as Channel Command Words (CCWs) to continue loading the startup program. When the I/O channel commands are complete, the first group of eight bytes is then loaded into the Program Status Word (PSW) register and the startup program begins execution at the designated location.[1]


Hard reboot

A hard reboot (also known as a cold reboot, frozen reboot, cold boot or cold start) is when power to a computer is cycled (turned off and then on) or a special reset signal to the processor is triggered (from a front panel switch of some sort). This restarts the computer without first performing any shut-down procedure. (With many operating systems, especially those using disk caches, after a hard reboot the filesystem may be in an "unclean" state, and an automatic scan of on-disk filesystem structures will be done before normal operation can begin.) It may be caused by power failure, be done by accident, or be done deliberately as a last resort to forcibly retrieve the system from instances such as a critical error or virus-inflicted DoS attack. Die of an Intel 80486DX2 microprocessor (actual size: 12×6. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ... Look up cache in Wiktionary, the free dictionary. ... Groups I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (-)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A virus (from the Latin noun virus, meaning toxin or poison) is a microscopic particle (ranging in size from 20 - 300 nm) that can infect the... In computer security and crime, a denial-of-service attack (DoS attack) is an attempt to make a computer resource unavailable to its intended users. ...


Soft reboot

A soft reboot (also known as a warm reboot) is restarting a computer under software control, without removing power or (directly) triggering a reset line. It usually, though not always, refers to an orderly shutdown and restarting of the machine. For delivered electrical power, see Electrical power industry. ... The phrase or term shut down, shut-down or shutdown can be used to mean turning off something, but most commonly used for machines or industrial plants such as computers, engines, nuclear reactors, petroleum refineries, fossil fuel power plants, and petrochemical plants. ...


The Control-Alt-Delete key combination on the original IBM PC was designed to allow a soft reboot for a quicker and more convenient (and, some argue, less stressful on system components) restart than powering the computer completely down then back up.[citation needed] This article is about Control-Alt-Delete, the keyboard shortcut. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ...


The Linux kernel has optional support for the kexec system call, which shuts down the currently running kernel and executes another one. The entire process is done independent of the system firmware. Note that the kernel being executed does not have to be a Linux kernel. In computing, a system call is the mechanism used by an application program to request service from the operating system. ...


Random reboot

Random reboot is a non-technical term referring to an unintended (and often undesired) reboot for which the cause is not immediately evident to the user. Such reboots may occur due to a multitude of software and hardware problems, such as triple faults. A soft reboot (also known as a warm reboot, in contrast to a cold reboot) is restarting a computer under software control, without removing power or (directly) triggering a reset line. ... 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 trying to invoke a regular exception handler. ...


As Windows XP has an option to skip its Blue Screen of Death and immediately restart the computer in the event of a fatal fault, users can be mistaken in thinking a Windows XP computer suffers from random rebooting. On a Unix and Unix-like systems it is known as a kernel panic, and these too can sometimes restart the computer. A public payphone has failed and is displaying the Blue Screen of Death. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®) is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... Diagram of the relationships between several Unix-like systems A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ... The Mac OS X kernel panic alert Kernel panic on a Linux 2. ...


Errors

In Windows, when an error occurs in the boot process, a Blue Screen of Death or a Black Screen of Death may occur. A public payphone has failed and is displaying the Blue Screen of Death. ... It has been suggested that this article or section be merged into Black Screen of Death. ...


References

  1. ^ a b z/Architecture Principles of Operation. IBM, Chapter 17. Retrieved on 2007-04-14. 

International Business Machines Corporation (known as IBM or Big Blue; NYSE: IBM) is a multinational computer technology and consulting corporation headquartered in Armonk, New York, USA. The company is one of the few information technology companies with a continuous history dating back to the 19th century. ... 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... April 14 is the 104th day of the year (105th in leap years) in the Gregorian calendar, with 261 days remaining. ...

See also

The following tables compare general and technical information for a number of available BOOT loaders. ... The Windows NT Startup Process is the process by which Microsofts Windows NT, Windows 2000, Windows XP and Windows Server 2003 operating systems initialize. ... This article or section is in need of attention from an expert on the subject. ... RedBoot is an open source application that uses the eCos real-time operating system Hardware Abstraction Layer to provide bootstrap firmware for embedded systems. ... Microreboot is a technique used to recover from failures in software systems. ... A boot disk is a removable media, normally read-only, that can boot an operating system or utility. ... Gnoppix 0. ... U3 LLC is a joint venture that is backed by Sandisk and its subdsidiary, M-Systems. ... A flash drive, related to a solid state drive, is a storage device that uses flash memory rather than conventional spinning platters to store data. ... Crash-only software refers to computer programs that handle failures by simply restarting, without attempting any sophisticated recovery. ... It has been suggested that this article or section be merged into Black Screen of Death. ... Network booting is the process of booting a computer from a network rather than a local drive. ...

Further reading

Look up bootup in
Wiktionary, the free dictionary.

 
 

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