Computer startup sequence

 

First, we will introduce two basic and important concepts.

BiOS: "Basic Input/Output System" (Basic Input/Output System). It is a set of programs that are "Solidified" and are directly associated with hardware in a ROM on the computer motherboard, stores the most important basic computer input and output programs, system settings, post-boot self-check programs, and system self-start programs, its main function is to provide the most basic and direct hardware settings and control for the computer, including the system BIOS (motherboard BIOS ). bios of other devices (such as the IDE controller bios and video card BIOS) is dominant. during the startup of a computer, BIOS is started under its control.

Memory Address: I mentioned it in my introduction to virtual memory. We know that the most basic unit of memory space is bit. 8 bits are regarded as one byte, that is, the commonly used unit of B, each byte in the memory occupies an address (the address is expressed in hexadecimal notation for the CPU to recognize the space ), the earliest 8086 processor can only recognize 1 MB (2 to the power of 20 B) space, which is known as the basic memory at the low end (that is, the end) of 1 MB, the remaining memory (all) is the extended memory. The 640kb space is obtained by the video memory and bios respectively.

Detailed introduction to the computer startup process (from power on to operating system startup)

1. When the power switch is down, the power supply starts to power the motherboard and other devices. The voltage is unstable, when the Main Board considers that the voltage does not meet the voltage required by the CPU clock speed recorded in CMOS, it will send a reset signal to the CPU (that is, reset to prevent the CPU from further running ), however, when the voltage is unstable in an instant, it can reach the required stable value. At this time, the reset signal is canceled, and the CPU immediately reads a jump instruction from the BIOS segment of the basic memory, jump to the real startup code of the BIOS. In this way, the system BIOS starts and the subsequent processes are controlled by the system BIOS.

2. After the system BIOS is started, it will perform power on self rest post (power on self rest ). However, this process is very fast. It mainly checks the existence of key devices (such as power supply, CPU chip, BIOS chip, basic memory, and other circuits, and whether the power supply is good. If there is a problem with self-check, the system speaker will make a beep (based on the length and frequency of the beep, you can know what the problem has occurred ).

3. If the self-check succeeds, the system BIOS searches for the video card bios, and then calls the initialization code of the video card BIOS, at this time, the display starts to display (that is why the self-check fails only by voice reminders ). The video card BIOS displays information about the video card on the screen (but this does not appear in the current notebook ).

4. After the video card is detected successfully, other devices will be tested. After passing the test, the system BIOS will re-execute its own code, display its own startup screen, and display its related information on the screen, then we will conduct a memory test (these will not be seen on the current computer). The system BIOS settings page will only appear for a short time, so we can set the system BIOS as needed, the system restarts.

5. Later, the BIOS will check the system's standard hardware (such as hard disk, soft drive (although many computers do not have a soft drive), serial and parallel interfaces ), after the detection is complete, the plug-and-play device is detected. If yes, resources such as interrupt, DMA channel, and I/O port are allocated to the device, all the devices have been detected. The old opportunity is to clear the screen and display a system configuration table. If the hardware changes compared with the previous startup, the BIOS will update the escd, extended system configuration data is the data used by the system BIOS to exchange hardware configuration information with the operating system. The data is stored in CMOS. The current machine will no longer display this.

6. After all the above steps are successfully performed, the BIOS will execute the last task: Start the system according to the user-specified startup sequence (that is, the frequently used setting where the system starts, generally, it is a hard disk by default. If you need to install the system, it will also be set to an optical drive or a USB device). Note that this refers to the boot sequence. If it is set to start from the optical drive, if there is no cd in the optical drive, the system will continue to start from the hard disk.

 

First, we will introduce two basic and important concepts.

BiOS: "Basic Input/Output System" (Basic Input/Output System). It is a set of programs that are "Solidified" and are directly associated with hardware in a ROM on the computer motherboard, stores the most important basic computer input and output programs, system settings, post-boot self-check programs, and system self-start programs, its main function is to provide the most basic and direct hardware settings and control for the computer, including the system BIOS (motherboard BIOS ). bios of other devices (such as the IDE controller bios and video card BIOS) is dominant. during the startup of a computer, BIOS is started under its control.

Memory Address: I mentioned it in my introduction to virtual memory. We know that the most basic unit of memory space is bit. 8 bits are regarded as one byte, that is, the commonly used unit of B, each byte in the memory occupies an address (the address is expressed in hexadecimal notation for the CPU to recognize the space ), the earliest 8086 processor can only recognize 1 MB (2 to the power of 20 B) space, which is known as the basic memory at the low end (that is, the end) of 1 MB, the remaining memory (all) is the extended memory. The 640kb space is obtained by the video memory and bios respectively.

Detailed introduction to the computer startup process (from power on to operating system startup)

1. When the power switch is down, the power supply starts to power the motherboard and other devices. The voltage is unstable, when the Main Board considers that the voltage does not meet the voltage required by the CPU clock speed recorded in CMOS, it will send a reset signal to the CPU (that is, reset to prevent the CPU from further running ), however, when the voltage is unstable in an instant, it can reach the required stable value. At this time, the reset signal is canceled, and the CPU immediately reads a jump instruction from the BIOS segment of the basic memory, jump to the real startup code of the BIOS. In this way, the system BIOS starts and the subsequent processes are controlled by the system BIOS.

2. After the system BIOS is started, it will perform power on self rest post (power on self rest ). However, this process is very fast. It mainly checks the existence of key devices (such as power supply, CPU chip, BIOS chip, basic memory, and other circuits, and whether the power supply is good. If there is a problem with self-check, the system speaker will make a beep (based on the length and frequency of the beep, you can know what the problem has occurred ).

3. If the self-check succeeds, the system BIOS searches for the video card bios, and then calls the initialization code of the video card BIOS, at this time, the display starts to display (that is why the self-check fails only by voice reminders ). The video card BIOS displays information about the video card on the screen (but this does not appear in the current notebook ).

4. After the video card is detected successfully, other devices will be tested. After passing the test, the system BIOS will re-execute its own code, display its own startup screen, and display its related information on the screen, then we will conduct a memory test (these will not be seen on the current computer). The system BIOS settings page will only appear for a short time, so we can set the system BIOS as needed, the system restarts.

5. Later, the BIOS will check the system's standard hardware (such as hard disk, soft drive (although many computers do not have a soft drive), serial and parallel interfaces ), after the detection is complete, the plug-and-play device is detected. If yes, resources such as interrupt, DMA channel, and I/O port are allocated to the device, all the devices have been detected. The old opportunity is to clear the screen and display a system configuration table. If the hardware changes compared with the previous startup, the BIOS will update the escd, extended system configuration data is the data used by the system BIOS to exchange hardware configuration information with the operating system. The data is stored in CMOS. The current machine will no longer display this.

6. After all the above steps are successfully performed, the BIOS will execute the last task: Start the system according to the user-specified startup sequence (that is, the frequently used setting where the system starts, generally, it is a hard disk by default. If you need to install the system, it will also be set to an optical drive or a USB device). Note that this refers to the boot sequence. If it is set to start from the optical drive, if there is no cd in the optical drive, the system will continue to start from the hard disk.