Data recovery base – 6. Computer running processes
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1.2 computer startup process
To further understand the file system, you must understand the basic operation of the process some of the computer.
1.2.1 Basic Concepts
1. Central processor
Central processor (Central Processing Unit, CPU) is the heart of the computer accessories, the brand has Intel's Pentium, Itanium, AMD's Athlon, Motorola's PowerPC and Sun's UltraSPARC and so on. CPU is the core of computing and control the computer.
2. Machine code
Although having a high-speed CPU processing power, but is not able to work autonomously. It's like a calculator, although computing speed quickly, but it must be input before the numerical computation computing needs. The CPU is the same, it can only be handled in accordance with the corresponding computation requirements of the people, human-computer interaction is through the "instruction" conducted - can be directly recognized by the computer instructions called machine code. Removed from the memory or the CPU cache instruction into the instruction register, and the instruction is decoded. It is the instruction into a series of micro-operations, and then issue a variety of control commands, execute micro-ops series, thus completing the execution of an instruction. Computer instruction is specified types of basic commands to perform operations and operands.
3. The boot code
We just mentioned, CPU is the core of the computer, and you need to be able to work instructions. Therefore, when the computer starts, you need to first find some CPU instruction - boot code. All volumes and file systems have a specific location to store boot code, but not all of the codes are often used.
4. BIOS (Basic Input Output System)
BIOS is dealing directly with the hardware underlying code, which provides for the operating system to control the basic functions of the hardware device. Including the system BIOS BIOS (that is often said motherboard BIOS), video card BIOS and other devices BIOS, the computer startup process is under the control of the system BIOS. BIOS is typically stored in ROM (read only memory chips) among even after shutdown or power down, the code does not disappear.
5. Memory address
Our machines are generally equipped with 512MB, 1GB or 2GB memory, which each byte is assigned an address, so that the CPU accesses memory. Earlier computer memory is not so big, usually 32MB, 64MB or address ranges 128MB, 32MB with a hexadecimal number is 0 ~ 1FFFFFFH.
The computer's boot process 1.2.2
Are the first to detect the hardware Most computer starts, and then load the operating system, applications. Here we are introduced to the Windows operating system, for example the computer startup process.
1st step : Power-On Self Test, self-test after power
(1) When you press the power switch, power began to supply the voltage stability, CPU starts executing instructions from a specific location to the motherboard and other devices.
(2) then the system BIOS startup code POST (Power-On Self Test, Power-On Self Test).
 2nd Step : BIOS initial detection
(1) The next system BIOS looks for the video card BIOS program and other equipment, internal call these BIOS initialization code to initialize after find related equipment.
(2) After completion of all other devices find BIOS, the system BIOS will show its own startup screen, including the contents of the system BIOS type, serial number and version number.
(3) Then the system BIOS detects and displays the CPU type and frequency, and then began to test all of RAM, and also shows the progress of the memory test on the screen.
 3rd step : BIOS hardware detection
(1) Following the adoption of the memory test, the system BIOS will start to detect some of the standard hardware devices installed in the system, including hard disks, CD-ROM, serial, parallel, floppy and other equipment, in addition to the vast majority of the newer version of the system BIOS in this the process also automatically detect and set the timing parameters of memory, hard disk parameters and access modes.
(2) Standard equipment testing is completed, the system supports Plug and Play BIOS code inside will begin to detect and configure Plug and Play devices installed in the system, each find a device, the system BIOS will be displayed on the device screen The name and model information, while assigned to the device interrupts, DMA channels, and I / O ports and other resources.
All hardware has been detected after the configuration is complete, the majority of the system BIOS will clear the screen and again at the top of the screen shows a table which lists the various standards roughly hardware devices installed in the system, and the resources they use and some related operating parameters.
4th Step : Update ESCD (Extended System Configuration Data, Extended System Configuration Data)
Next, the system BIOS will update ESCD (Extended System Configuration Data, Extended System Configuration Data). ESCD is the hardware configuration of the system BIOS as a means for the exchange of information with the operating system, the data is stored in the CMOS (a small piece of special RAM, the battery on the motherboard to the power supply) into.
 5th Step : Selecting the boot sequence
After ESCD update is complete, the system BIOS boot code will be its last task that, according to the boot sequence specified by the user from a floppy disk, hard disk or CD-ROM boot.
To boot from the C drive, for example, the system BIOS will read and execute on the primary hard disk boot record, master boot record and then find the first active partition from the partition table, and then reads and executes the active partition boot record partition, The partition boot record will be responsible for reading and executing IO.SYS, and further guidance and boot the system.
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