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The booting process

The booting process. Whenever you turn on your computer, the first thing you see is the BIOS software. On many machines, the BIOS displays text describing things like the amount of memory installed in your computer, the type of hard disk and so on.

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The booting process

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  1. The booting process • Whenever you turn on your computer, the first thing you see is the BIOS software. • On many machines, the BIOS displays text describing things like the amount of memory installed in your computer, the type of hard disk and so on. • during the boot sequence, the BIOS is doing a remarkable amount of work to get your computer ready to run.

  2. When you turn on your computer and the microprocessor tries to execute its first instruction, it has to get that instruction from somewhere. It cannot get it from the operating system because the operating system is located on a hard disk, and the microprocessor cannot get to it without some instructions that tell it how. The BIOS provides those instructions.

  3. The booting process

  4. An Overview Of The Boot Sequence • When power is applied, the system resets all of the logic gates (chips) to a known state. • A series of diagnostic tests (Power-On Self- Test, or POST) are run from the PROM Monitor to ensure that some minimal set of hardware components are available for system operation. • Once the POST operation completes, the system loads a small “boot loader” program from the system PROM. • The boot-loader loads the system boot block.

  5. Computer Startup • bootstrap program is loaded from boot block. • Typically stored in ROM or EPROM, generally known as firmware • Initializates all aspects of system • Loads operating system kernel and starts execution

  6. Boot Sequence • What happens when you turn the computer on? • CPU reset: when turned on, CPU is reset and BIOS is activated • Power-On Self Test (POST) performed by BIOS: • Verify integrity of CPU and POST • Verify that all components functioning properly • Report if there is a problem (beeps) • Instruct CPU to start boot sequence

  7. BIOS Functioning • the BIOS does several things. This is its usual sequence: • Check the CMOS (complementary metal oxide semiconductor) Setup for custom settings • Load the interrupt handlers and device drivers • Initialize registers and power management • Perform the power-on self-test (POST) • Display system settings • Determine which devices are bootable • Initiate the bootstrap sequence

  8. The booting process Main memory ROM Secondary storage RAM

  9. The booting process Main memory Bootstrap program ROM Secondary storage Operating system RAM

  10. The booting process Load OS Execute OS Main memory Bootstrap program ROM Secondary storage Operating system RAM

  11. The booting process Load OS Main memory Bootstrap program ROM Secondary storage Operating system RAM

  12. The booting process Load OS Main memory Bootstrap program ROM Secondary storage Operating system RAM

  13. The booting process Main memory Bootstrap program ROM Secondary storage Operating system RAM OS in memory

  14. The booting process Load OS Execute OS Main memory Bootstrap program ROM Secondary storage Operating system RAM OS running from memory

  15. Quick Review • The computer loads the basic input/output system (BIOS) from ROM. The BIOS provides the most basic information about storage devices, boot sequence, security, Plug and Play . • The computer loads data from read-only memory (ROM) and performs a power-on self-test (POST) to make sure all the major components are functioning properly.

  16. The computer loads the operating system (OS) from the hard drive into the system's RAM. Generally, the critical parts of the operating system are maintained in RAM as long as the computer is on. • This allows the CPU to have immediate access to the operating system, which enhances the performance and functionality of the overall system. • When you open an application, it is loaded into RAM. To conserve RAM usage, many applications load only the essential parts of the program initially and then load other pieces as needed. • After an application is loaded, any files that are opened for use in that application are loaded into RAM.

  17. When you save a file and close the application, the file is written to the specified storage device, and then it and the application are purged from RAM.

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