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Anusha BABOOA




10/7/2012       1
1. Introduction
2. The bootloader
3. Device drivers
4. Boot sequence on a standard PC
5. Outputting the results of an addition
6. Summary




10/7/2012     Booting steps of a computer   2
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
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
 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
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
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
 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 software


10/7/2012      Booting steps of a computer                  8
Network booting
o 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
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 card



10/7/2012      Booting steps of a computer                 10
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
 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 MBR's 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
 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 partition's
  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
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
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
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
 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
Summary
Outline 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
http://www.phrases.org.uk/meanings/290800.html.
^ "Bootstrap". Dictionary.com.
http://dictionary.reference.com/search?r=2&q=bootstrap.
^ "Bootstrap". TheFreeDictionary.com.
http://www.thefreedictionary.com/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".
http://www.multicians.org/mgb.html. Retrieved 2010-01-18.
^ Bensoussan, A. (1967-06-30). "BC.4.01 System Initialization
and Bootload". Multics System Programmer's Manual.
http://www.multicians.org/mspmtoc.html.
^ Dunten, S. D.; T. H. Van Vleck (1968-05-03). "BV.1.01 BOS
Bootload: boot". Multics System Programmer's Manual.
http://www.multicians.org/mspmtoc.html.

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booting steps of a computer

  • 2. 1. Introduction 2. The bootloader 3. Device drivers 4. Boot sequence on a standard PC 5. Outputting the results of an addition 6. Summary 10/7/2012 Booting steps of a computer 2
  • 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. 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.  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. 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. 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.  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 software 10/7/2012 Booting steps of a computer 8
  • 9. Network booting o 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. 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 card 10/7/2012 Booting steps of a computer 10
  • 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.  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 MBR's 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.  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 partition's 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. 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. 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. 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.  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. Summary Outline 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. http://www.phrases.org.uk/meanings/290800.html. ^ "Bootstrap". Dictionary.com. http://dictionary.reference.com/search?r=2&q=bootstrap. ^ "Bootstrap". TheFreeDictionary.com. http://www.thefreedictionary.com/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". http://www.multicians.org/mgb.html. Retrieved 2010-01-18. ^ Bensoussan, A. (1967-06-30). "BC.4.01 System Initialization and Bootload". Multics System Programmer's Manual. http://www.multicians.org/mspmtoc.html. ^ Dunten, S. D.; T. H. Van Vleck (1968-05-03). "BV.1.01 BOS Bootload: boot". Multics System Programmer's Manual. http://www.multicians.org/mspmtoc.html.