What is the operating system?
You might think so, windows, unix, linux, macos, Android, ios .... all operating systems. This understanding is not wrong, but too superficial.
Operating system runs directly on the hardware of a computer program .
Operating system for managing and controlling computer hardware and software resources
Operating system for the user software to provide the necessary development services and interfaces
Modern computer systems architecture:
BIOS——Base Input & Output System
BIOS is powered on after the computer program that runs the
BIOS first state detection hardware, hardware initialization immediately after detected by
BIOS memory will establish the interrupt vector table (provided hardware access methods)
Finally BIOS transfers control handed over to the master boot program execution
Note: BIOS not software (software), but the firmware (firmware)
Firmware is cured in hardware program, programmed in the factory prior to hardware fixed
System boot process (X86 architecture)
BIOS loads the master boot program, the master boot program to load the operating system kernel, then the BIOS is to load it who runs it?
BIOS operating mechanism:
--BIOS stored in the ROM, the address mapping for 0xF0000--0xFFFFF (real address)
--BIOS entry address is: 0xFFFF0
- Special hardware design is such that:
Boot, cpu started from 0xFFFF0 place.
As can be seen from the above, no other program to load the BIOS, which is designed so that a special hardware circuit, boot, cpu execution begins at 0xFFFF0.
BIOS's last mission
Provided by the user scanning the respective storage medium (CD-ROM, floppy disk, U disk, etc.)
After the master boot found, the master boot program loaded in the master boot memory
The master boot program entry address in memory is 0x7c00
The control program executed referred main guide (jmp 0x7c00). Control over how to pay out? Jmp is achieved by a single assembly instruction.
How to find BIOS master boot program in the storage medium?
How to determine the master boot there is no master boot program ?
Master boot sector (the MBR: the Record the Boot Master)
- position: located at the beginning of the storage medium, a size of 512 bytes
- Features: the first 512 bytes of the last two bytes of valid 0x55AA (master boot program determines the legality of the sign)
- data: data before 0x55aa is considered the primary boot program
Question 1: Is the first 512 bytes of each storage media, the master boot program is
not.
Question 2: If you have already pre-judged that 512 bytes is the master boot, then the data is legitimate master boot program it does not store the master boot it?
Not necessarily
More detailed system boot process (X86 architecture)
Summary:
BIOS is the first program after power run on a computer
BIOS initializes necessary, and run the master boot program loads
the master boot program is located at the beginning of the storage medium 512 bytes of
the master boot program is responsible for a subsequent initialization, run and load operation system kernel