Opening the power start machine is almost a matter of computer enthusiasts every day, facing a boot screen appearing on the screen, we will not feel unfamiliar, but what is the computer done when the computer is displayed? what about work? I believe that some friends are not very clear, this article will introduce what is done when the computer has done from the open power to the blue sky, the computer. Let us first understand some basic concepts. The first is a very familiar BIOS (Basic Input Output System), BIOS is the underlying code that is dealt with hardware, which provides the operating system to control the basic functions of the hardware device. BIOS includes BIOS with system BIOS (i.e. often said motherboard BIOS), graphics card BIOS and other devices (such as IDE controller, SCSI card or network card, etc.), wherein the system BIOS is the protagonist to be discussed herein because the computer's startup process is It is carried out under its control. BIOS is generally stored in the ROM (read-only memory chip), and these code will not disappear even after turning off or powered down. The second basic concept is the address of the memory, and 32MB, 64MB, or 128MB memory is generally installed in our machine, each byte of these memory is given an address so that the CPU has access to memory. The 32MB address range is indicated by hexadecimal number is 0 ~ 1ffffh, where 0 ~ FFFFH low end 1MB memory is very special, because the initial 8086 processor can access the maximum memory only 1MB, this 1MB low end 640KB is called For basic memory, and A00H ~ bffffh is preserved to use the display card, C0000h ~ fffh is preserved to BIOS, where the system BIOS generally occupies the last 64KB or more space, the graphics card BIOS is generally at C0000h ~ C7FFFH The BIOS of the IDE controller is at C8000H ~ CBFFFH. Step 1: When we press the power switch, the power is powered to the motherboard and other devices. At this time, the voltage is not stable, and the control chipset on the motherboard will send an RESET (reset) signal to the CPU. Let the CPU automatically return to the initial state, but the CPU will not immediately perform the instructions immediately. When the chipset detected that the power supply has started to stabilize power (of course, from the unstable to a stable process is just a moment), it removes the RESET signal (if it is manually pressing the RESET button on the computer panel to restart the machine, then loose When the button is opened, the chipset will remove the RESET signal), and the CPU immediately starts executing instructions from the address FFF0H. From the previous introduction, this address is actually within the address range of the system BIOS, whether it is Award BIOS or Ami BIOS, Placing is just a jump instruction, jumps to the real start code in the system BIOS. Step 2: The system BIOS startup code is the first thing to do is to perform Post (Power-On Self Test, self-test after power-on), and the main task of POST is to detect some key devices in the system and whether it can work properly. For example, devices such as memory and graphics cards. Since POST is the earliest test process, the graphics card has not been initialized. If the system BIOS found some fatal errors during POST, for example, there is no memory or memory problem (at this point only 640K regular memory), Then the system BIOS will directly control the speaker to report the error, and the length of the sound represents the type of error.
Under normal circumstances, the POST process is very fast. We have almost unable to feel its presence, and other code will be called for more complete hardware detection after POST. Step 3: Next, the system BIOS will find the graphics card's BIOS, before, the start address of the ROM chip stores the graphics card BIOS is usually set at C0000h, and the system BIOS will call its initialization code after finding the graphics BIOS in this place. The graphics card is initialized by the graphics card BIOS. At this time, most graphics cards will show some initialization information on the screen, introduce manufacturers, graphic chip types, etc., but this picture is almost a flash. The system BIOS will then find the BIOS program of other devices. After finding, the initialization code to be called inside these BIOS is to initialize the relevant device. Step 4: After finding the BIOS of all other devices, the system BIOS will display its own boot screen, including the type, serial number and version number of the system BIOS. Step 5: The system BIOS will then detect and display the type and operating frequency of the CPU, then start testing all the RAM, and simultaneously display the progress of the memory test on the screen, we can decide to use the simple consumption in the CMOS settings or Detailed time consumption. Step 6: After the memory test passes, the system BIOS will start some standard hardware devices installed in the system, including hard drives, CD-ROMs, serial ports, parallel ports, floppy drives, etc., and most newer version of the system BIOS is here. The timing parameters, hard disk parameters, and access modes, etc. of the memory are also automatically detected and set in the process. Step 7: After the standard equipment is detected, the system BIOS inside the system BIOS will begin to detect and configure the plug-and-play device installed in the system. After finding a device, the system BIOS will display it on the screen. The name and model of the device, and the device allocates the interrupt, DMA channel, and I / O ports. Step 8: All hardware has been detected, and the multi-system BIOS will re-clear the screen and display a table on the screen, which roughly lists the various standard hardware devices installed in the system. And the resources they use and some related work parameters. Step 9: Next, the system BIOS will update the ESCD (Extended System Configuration Data). ESCD is a means of system BIOS to exchange hardware configuration information with operating systems, which are stored in CMOS (a small special RAM, powered by batteries on the motherboard). Usually the ESCD data will only be updated only after the system hardware configuration changes, so we can see information such as "Update Escd ... Success" when the machine is started, but the system BIOS of some motherboard is saved when ESCD data. Using the Data format with Windows 9x, Windows 9X modifies the ESCD data into its own format during its own startup process, but when the machine is started, even if the hardware configuration does not change, the system BIOS will also The ESCD's data format is changed, and this loop will cause the system BIOS to update the ESCD when the machine is started, which is why some machines will display relevant information at each time startup. Step 10: After the ESCD is updated, the system BIOS startup code will perform its last job, that is, start from the floppy disk, hard disk or optical drive from the floppy disk, hard disk, or optical drive according to the user-specified startup order.
