Booting and Halting

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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.


An Overview Of The Boot Sequence


The system executes the code from the boot block.
This program loads the secondary boot loader that will eventually load the operating system kernel and start it.
Most secondary boot loaders allow the operator to select the device to boot from, as well as the program that will be loaded into memory and started.


PC PROM Monitors

.PC BIOS
-Limited alternate boot device selection
Typically: Disk, CDROM, Floppy, and net.
Sometimes alternate disk boot is supported.
-Configure/modify hardware settings
Enable/disable device, change IRQ/memory ranges.
-Allows for device BIOS interaction