Transcript Slide 1
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
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
BIOS
The BIOS primary functions are
Issue the instructions for starting the hardware
at boot time.
Load the OS from the boot device.
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.
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.
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.
BIOS: User Interface
There is a curses based user interface that
allows:
a)Selection of a boot device
b)Setting the system clock
c)Configuring hardware (includes enabling or
disabling some devices)
d)Setting passwords for booting, & the UI, etc.
e)Also shows access to some system config
information: memory size, disk size, etc.
BIOS Completion
Memory count
Search for the OS Boot device
Optical drive
USB device
Network device
HDD
HDD Boot Sequence
If the HDD is the boot device then, ...
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.
HDD Boot Sequence
The boot code will do one of two things when
executed:
1. Load a boot loader (GRUB, LILO, MS-BM)
1. Allows one to choose from different OSes or
different versions of the same OS.
2. Load the OS if no boot loader is available.
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.
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.
BIOS/UEFI
BIOS is often used to describe UEFI
Modern OSes allow backward compatibility
between the traditional BIOS boot record and
the UEFI GPT.
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.)