booting steps of a computer


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booting steps of a computer

  1. 1. Presented by:Anusha BABOOA10/7/2012 1
  2. 2. 1. Introduction2. The bootloader3. Device drivers4. Boot sequence on a standard PC5. Outputting the results of an addition6. Summary10/7/2012 Booting steps of a computer 2
  3. 3. Introduction In computing, booting (also known as "booting up") is a bootstrapping process that starts operating systems when the user turns on a computer system. A boot sequence is the initial set of operations that the computer performs when power is switched on. The bootloader typically loads the main operating system for the computer.10/7/2012 Booting steps of a computer 3
  4. 4. The boot loader Modern operating systems and application program code and data are stored on nonvolatile data storage devices, such as hard disk drives, CD, DVD, flash memory cards, USB flash drives disks. When switched on, the computer runs a relatively small program (known as bootstrap loader or boot loader) stored in ROM along with the least amount of data needed to access the non-volatile devices from which operating system programs and data are loaded into RAM.10/7/2012 Booting steps of a computer 4
  5. 5.  The main task of the bootloader is to load other data and programs which are then executed from RAM. Multiple- stage boot loaders are usually used which loads several complex programs one after the other in a process of chain-loading. Computers often use automatic bootload mechanisms to ensure that it starts quickly and with a predetermined software configuration e.g., in desktop computers bootstrapping starts with the CPU executing software(e.g., BIOS )found le tin ROM at a predefined address.10/7/2012 Booting steps of a computer 5
  6. 6. Common primary boot loaders: BIOS (Basic Input/Output System) EFI (Extensible Firmware Interface) Open BIOS SLOF (Slimline Open Firmware) These software contain essential functionality to search for devices eligible to participate in booting.10/7/2012 Booting steps of a computer 6
  7. 7. Second stage bootloader Small program is most often not itself an operating system but only a second stage boot loader such as GRUB, BOOTMGR, Syslinux, NTLDR, LILs The OS initializes itself and may load device driver needed for the normal operations of the OS. After that it starts loading normal system programs. Bootloaders can be configured to give the user multiple booting choices including different versions, loading options of the operating system.10/7/2012 Booting steps of a computer 7
  8. 8.  Usually a default choice is preselected with a time delay which a user can press a key to change the choice, after which the default choice is automatically run, so normal booting can occur without interaction. Boot process is complete when the computer is ready to interact with the user or the OS is capable of running system programs or application program like spreadsheet, word processor. Typical personal computers boot in about 1 minute among which 15 seconds are taken by the power-on- self-test (POST) and a preliminary boot loader and the rest by loading the OS and other software10/7/2012 Booting steps of a computer 8
  9. 9. Network bootingo Most computers are also capable of booting over computer network.o 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.o After these parts have been transferred, the operating system then takes over control of the booting process.10/7/2012 Booting steps of a computer 9
  10. 10. Boot devices The boot device is the device from which the operating system is loaded. A modern PC BIOS supports booting from various devices, typically a local hard disk drive (or one of several partitions on such a disk), an optical disk drive, a USB device (flash drive, hard disk drive, optical disc drive, etc.), a flash memory card such as an SD card in a multi-media card slot, or a network interface card10/7/2012 Booting steps of a computer 10
  11. 11. Boot sequence on standard PC Power supply sends signal to components in system unit The CPU of the personal computer executes instruction located at the memory location of the BIOS, stored in ROM, which is located at the 0xFFFF0 linear address to start the computer. BIOS performs a POWER ON SELF TEST (POST test), to check components such as mouse, keyboard connectors, and expansion cards, in essence, the BIOS is taking inventory The BIOS goes through a pre-configured list of boot device sequence until it finds one that can be read (bootable)from the boot signature.10/7/2012 Booting steps of a computer 11
  12. 12.  Results of the POST are compared to data in the CMOS chip, the CMOS knows what is supposed to be detected. If something is missing, the computer will alert you with a tone, or an on-screen message. BIOS looks for boot files in a CD drive, or another drive such as a USB flash drive, if present. If it finds no boot files, it then looks to drive C Once BIOS has found a bootable device, it loads the boot sector and transfers execution to the master boot record (MBR). The MBR code checks the MBRs partition table for a partition set as bootable. If an active partition is found, the MBR code loads the boot sector code from that partition and executes it.10/7/2012 Booting steps of a computer 12
  13. 13.  The main function of the boot sector is to load and execute the operating system kernel, which continues startup. If there is no active partition, or the active partitions boot sector is invalid, the MBR may load a secondary boot loader which will select a partition (often via user input) and load its boot sector, which usually loads the corresponding operating system kernel into RAM from boot drive. Once the operating system is loaded in memory, it takes control of computer. Operating system loads configuration information and displays desktop on screen. OS executes any programs In Start Up folder and the computer is ready to use.10/7/2012 Booting steps of a computer 13
  14. 14. Power on self test (POST) The computer power-on self-test tests the computer to make sure it meets the necessary system requirements and that all hardware is working properly before starting the remainder of the boot process. If the computer passes the POST, the computer may have a single beep (with some computer BIOS suppliers it may beep twice) as the computer starts and the computer will continue to start normally.10/7/2012 Booting steps of a computer 14
  15. 15. Booting Digital Signal Processors When, a DSP and a CPU or a microcontroller are co- existing, the boot sequence is as following. The DSP is booted by another processor which is called Host processor or also Master because it usually boots first from its own memories and then controls the overall system behaviors (that means booting of the DSP and further controlling the DSP’s behavior). What is interesting here is that often the DSP lacks its own boot memories and relies on the boot processor to supply the required code instead. Examples of systems with such a design are cell phones, modems, audio and video player. 10/7/2012 Booting steps of a computer 15
  16. 16. Outputting the results of an addition The processor is composed by a control unit (which controls the operations of a computer) and a Arithmetic Logic Unit (which performs mathematical calculations). When a computer performs an addition, two signal ALUs operate in series based on signals received from the control unit. The pixel input streams and two constant values are input to a multiplexer and delay circuit The multiplexer and delay circuit chooses among these inputs to produce two inputs to the system.10/7/2012 Booting steps of a computer 16
  17. 17.  The two system inputs are coupled to the first ALU wherein the ALU performs its operation on the two inputs based on instructions from the control unit. The output from this ALU is input to another multiplexer and delay circuit wherein the inputs to the second ALU may be selected. The multiplexer and delay circuit selects from among the two original ALU inputs, the output from the first ALU and one of the constants originally input to the first multiplexer and delay circuit to produce two input values for the second ALU. After the control unit evaluates the output from the first ALU, the second ALU performs its operation on these two values based on instructions from the control unit. The result of the second operation is communicated to an output latch which forms a one-bit output stream and a 16-bit output stream.10/7/2012 Booting steps of a computer 17
  18. 18. SummaryOutline of the boot sequence Phase Post BIOS is started. Some basic hardware checks are performed. Hardware is Boot sector takes over the Power on identified and initialized. BIOS computer and begins to kernel looks for a boot sector in the start an operating system. order of the devices specified by the BIOS setiing. GUI and System startup init beyond 10/7/2012 Booting steps of a computer 18
  19. 19.^ "Bootstrap".^ "Bootstrap".^ Oxford English Dictionary. Oxford University.^ From Gutenberg to the Internet, Jeremy M. Norman, 2005,page 436, ISBN 0-930405-87-0^ Van Vleck, Tom. "Glossary of Multics acronyms and terms". Retrieved 2010-01-18.^ Bensoussan, A. (1967-06-30). "BC.4.01 System Initializationand Bootload". Multics System Programmers Manual.^ Dunten, S. D.; T. H. Van Vleck (1968-05-03). "BV.1.01 BOSBootload: boot". Multics System Programmers Manual.