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Hardware Boot Sequence

Hardware Boot Sequence. Vocabulary. BIOS = Basic Input Output System UEFI = Unified Extensible Firmware Interface POST= Power On Self Test BR = Boot Record (aka MBR) BC = Boot Code (aka MBC) GUID = Globally Unique Identifier GPT = GUID Partition Table. BIOS.

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Hardware Boot Sequence

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  1. Hardware Boot Sequence

  2. Vocabulary • BIOS = Basic Input Output System • UEFI = Unified Extensible Firmware Interface • POST= Power On Self Test • BR = Boot Record (aka MBR) • BC = Boot Code (aka MBC) • GUID = Globally Unique Identifier • GPT = GUID Partition Table

  3. BIOS • Instructions used to start the computer from a cold start. (power off to power on). • The BIOS instructions are written on non-volatile RAM. • EEP-ROM is the common media choice for the BIOS, installed on the motherboard. • The BIOS instructions are based on the chip-set installed on the motherboard

  4. BIOS • The BIOS primary functions are • Issue the instructions for starting the hardware at boot time. • Load the OS from the boot device.

  5. Hardware Boot Sequence • Turn on the power switch • All memory and cache is empty at startup. • A reset signal is generated by the chipset to the CPU until the power is ready. • The CPU powers up and reads address xFFFF0 from the ROM. This contains a jump instruction to the start of the BIOS instructions.

  6. POST • The POST (Power On Self Test) • Provide power to the motherboard-speaker • This allows error-code signals to be broadcast by the mobo-speaker when errors are detected • Test if components on the motherboard are receiving power and functioning as intended.

  7. Hardware Boot Sequence • Video and keyboard are activated early in the boot sequence. (video start instruction in ROM address is xC000) • Other devices are activated like the disk drives, optical drives, sound-card, NIC, USB bus, etc. • BIOS setup becomes available for the user.

  8. BIOS: User Interface • There is a curses based user interface that allows: • Selection of a boot device • Setting the system clock • Configuring hardware (includes enabling or disabling some devices) • Setting passwords for booting, & the UI, etc. • Also shows access to some system config information: memory size, disk size, etc.

  9. BIOS Completion • Memory count • Search for the OS Boot device • Optical drive • USB device • Network device • HDD

  10. HDD Boot Sequence • If the HDD is the boot device then, ...

  11. HDD Boot Sequence • The BR is read from the first cylinder, first track, first sector. • The BR contains the BC (boot code) and a partition table.

  12. HDD Boot Sequence • The boot code will do one of two things when executed: • Load a boot loader (GRUB, LILO, MS-BM) • Allows one to choose from different OSes or different versions of the same OS. • Load the OS if no boot loader is available.

  13. Partition Table • The PT contains information about 4 primary partitions. • Only one of the 4 primary partitions is designated as the active partition • The active partition contains the OS for booting. • One of the 4 primary partitions can be designated as the extended partition. • The extended partition can be divided into additional logical partitions.

  14. BIOS/UEFI • In the beginning there was the BIOS • Intel creates the Extensible Firmware Interface in 1998 • UEFI now supersedes EFI • UEFI can run on-top-of the traditional BIOS or in place of the BIOS.

  15. BIOS/UEFI • BIOS is often used to describe UEFI • Modern OSes allow backward compatibility between the traditional BIOS boot record and the UEFI GPT.

  16. GPT • Globally Unique Identifier – This is required to allow a file system to exceed 2TB. • The 2TB limit is a result of limitations of the original BR partition table • (Each partition has only16 bytes of storage in the partition table.)

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