发表于 2019-6-24 10:39
关键词: BIOS, Bootable device
What Is the BIOS Used For?
BIOS instructs the computer on how to perform a number of basic functions such as booting and keyboard control.
BIOS is also used to identify and configure the hardware in a computer such as the hard drive, optical drive, CPU, memory, etc.
How to Access Your BIOS
The BIOS is accessed and configured through the BIOS Setup Utility. The BIOS Setup Utility is, for all reasonable purposes, the BIOS itself. All available options in BIOS are configurable via the BIOS Setup Utility.
BIOS is pre-installed when the computer is purchased.
To access your BIOS, you’ll need to press a key during the boot-up process. This key is often displayed during the boot process with a message “Press F2 to access BIOS”, “Press <DEL> to enter setup”, or something similar. Common keys you may need to press include Delete, F1, F2, and Escape.
BIOS vs UEFI
UEFI stands for “Unified Extensible Firmware Interface”. It’s the successor to the traditional BIOS. If interesting, google it.
How does BIOS recognize a device as bootable?
Turns out, by magic numbers: 0x55 and 0xAA, or 85 and 170 in decimal appropriately.
These magic numbers are just markers for the BIOS to identify bootable devices from other devices.
When the BIOS finds such a boot sector, it is loaded into memory at specific address — 0x0000:0x7C00.
Now we know where we need to store the program so it can be loaded by the BIOS into memory.
From here you can make your own Operation System.