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A modern PC is configured to attempt to boot from various devices in a certain order. If a computer is not booting from the device desired, such as the floppy drive, the user may have to enter the BIOS Setup function by pressing a special key when the computer is first turned on (such as Delete, F1, F2, F10 or F12), and then changing the boot order. [6]
The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches. The BIOS checks each device in order to see if it is bootable by attempting to load the first sector (boot sector). If the sector cannot be read, the BIOS proceeds to the next device.
In the case of a hard reboot, the northbridge will direct a code fetch request to the BIOS located on the system flash memory. For a warm boot, the BIOS will be located in the proper place in RAM and the northbridge will direct the reset vector call to the RAM. In earlier PC systems, before chipsets were standard, the BIOS ROM would be located ...
When debugging a concurrent and distributed system of systems, a bootloop (also called boot loop or boot-loop) is a diagnostic condition of an erroneous state that occurs on computing devices; when those devices repeatedly fail to complete the booting process and restart before a boot sequence is finished, a restart might prevent a user from ...
In many desktop computers, for example, the bootstrapping process begins with the CPU executing software contained in ROM (for example, the BIOS of an IBM PC or an IBM PC compatible) at a predefined address (some CPUs, including the Intel x86 series, are designed to execute this software after reset without outside help).
BIOS interrupt calls perform hardware control or I/O functions requested by a program, return system information to the program, or do both. A key element of the purpose of BIOS calls is abstraction - the BIOS calls perform generally defined functions, and the specific details of how those functions are executed on the particular hardware of the system are encapsulated in the BIOS and hidden ...
This implies that after the hardware reset, the CPU will start execution at the physical address 0xFFFF0. In IBM PC compatible computers, This address maps to BIOS ROM. The memory word at 0xFFFF0 usually contains a JMP instruction that redirects the CPU to execute the initialization code of BIOS. This JMP instruction is absolutely the first ...
The Primary Bootloader (PBL), which is stored in the Boot ROM [3] is the first stage of the boot process. This code is written by the chipset manufacturer. [4]The PBL verifies the authenticity of the next stage.