A. Operating system
A. From this we can draw a doubt, what is the operating system?
1. In our daily life, Windows, UNIX, Linux, Mas OS , Android, ios , etc. is a common operating system
2. The operating system is run directly computer programs on hardware
3. the operating system used to manage and control the computer's hardware and software resources
4. the operating system provides the necessary services and user interfaces for software development
B. modern computer system architecture 
BIOS-Base Inout & Output system (Note the BIOS is not software, but firmware, hardware, firmware is cured in the program, before the hardware is factory programmed fixed)
1.BIOS program after power is first run on a computer
2.BIOS first check the hardware status, immediately after detection by the hardware initialization
3.BIOS will establish the interrupt vector table (provided hardware access methods) in memory
4.BIOS finally handed over control of the master boot program execution
system boot process (X86) 
operating mechanism of the BIOS
1. the BIOS is stored in ROM, the address mapping for 0xF0000-0xFFFFF (real address)
entry address is 2.BIOS: 0xFFFF0
after 3. specially designed hardware circuit such that power, the CPU apart from the 0xFFFF0 Begins executing
the final mission of the BIOS
1. In accordance with the respective user set the scan storage medium (CD-ROM, floppy disk, U disk, etc.)
2. master boot found, the master boot program in the master boot record loaded into memory
3. In the master boot program entry address in memory is 0x7C00
4. referred to the control of the main program (jmp 0x7c00)
Q: BIOS how to find the master boot in a storage medium? How to determine the boot sector there is no master boot program?
Master boot record (MBR: Master Boot Record)
position: located at the beginning of the storage medium, a size of 512 bytes
features: the first 512 bytes of the last two bytes 0x55aa valid
data: data is considered before 0x55aa the master boot program
system startup process after improvement 
Summary
1.BIOS programs after power is first run on a computer
2.BIOS necessary initialization, run and load the master boot program
3. the master boot program is located in the beginning of the storage medium 512 bytes
4. master boot program is responsible for a subsequent initialization, run and load the operating system kernel