1. Computer System Structures
System Operation
Computer System Operation
Boot Process
BIOS, UEFI
Loaders, Init
Interrupt Driven OS
Textbook Silberschatz, Chapter 2

2. Booting
The procedure of starting a computer by loading the kernel is known as booting the system.
On most computer systems, a small piece of code known as the bootstrap program or bootstrap loader
locates the kernel
loads it into main memory
and starts its execution.
Some computer systems, such as PCs, use a two-step process in which
a simple bootstrap loader fetches a more complex boot program from disk
which in turn loads the kernel.

3. After Reset CPU receives a reset event - powered up or rebooted
The instruction address register is loaded with a predefined memory location, and execution starts there.
At that location is the initial bootstrap program.
This program is in the form of read-only memory (ROM),
because the RAM is in an unknown state at system startup.
ROM is convenient because
it needs no initialization (keeps the content with power off computer)
and cannot easily be infected by a computer virus.

4. Bootstrap Program - Requirements. Firmware
The bootstrap program should be simple.
It should not be lost when the power is off. So it should reside somewhere in ROM.
It should know how to load the OS.
It should ensure that the hardware is OK.
The bootstrap program usually is the part of the larger entity called firmware – something between the hardware and software
Firmware is the combination of persistent memory and program code and data stored in it
It’s slow, expensive

5. The Booting Process, BIOS, UEFI, loaders, Init
The system’s component
Firmware(BIOS, UEFI, Uboot, bootstrap, ..)
Initial Boot Loader
OS Loader
Init (initial process)
Resides on …
ROM
EEPROM
HDD Master Boot Record
HDD Partition’s boot sector
Kernel
The Action
Power on.
Start the BIOS.
Initialize the system hardware.
Call IBL
Recognize HDD partitions.
Choose OS.
Call OS loader.
Load the OS (kernel).
Run kernel’s initial process.
All the time continuously run in the system waiting events.

6. Once more Interrupt driven OS
Modern operating systems are interrupt driven. If there are no processes to execute, no I/O devices to service, and no users to whom to respond, an operating system will sit quietly, waiting for something to happen.
The occurrence of an event is usually signaled by an interrupt from either the hardware or the software.