1. Background
A problem has been bothering me ever since I got into computers. What exactly happens when we press the power on button of the computer? What are the specific steps to start a computer?
The computer startup process is usually divided into five steps: power self-test, BIOS self-test, boot device selection, boot program loading and operating system loading.
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2. Power supply self-test
The abbreviation of power self-test is Power-On Self-Test, usually abbreviated as POST.
Power self-test is the first stage of the computer startup process. It mainly checks whether the computer's power system is working properly. At this stage, the computer performs the following self-test operations:
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Check whether the power supply is connected properly: The computer will check whether the power plug is plugged in tightly and whether the power cord is firmly connected. If the power plug is not plugged in tightly or the power cord is not connected securely, the computer will not work properly.
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Check whether the power switch is normal: The computer checks whether the power switch is on. If the power switch is off, the computer will not start.
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Check whether the power output is stable: The computer checks whether the power output is stable. Unstable power output will affect the normal operation of the computer and even damage the computer hardware.
If the power supply self-test passes, the computer will enter the next stage, the BIOS self-test. If the power self-test fails, the computer will not continue to boot, usually with an audible warning or an error message. In this case, users need to check whether the power connection is correct and repair the power failure to ensure that the computer can work properly.
3. BIOS self-test
BIOS self-test (Basic Input/Output System Self-Test) is the second step in the computer startup process. Its main function is to check whether the computer hardware is normal. BIOS is the basic input and output system on the computer, responsible for managing and controlling computer hardware devices.
The BIOS self-test process includes the following steps:
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Initializing the hardware: When the BIOS self-test starts, the BIOS will initialize the computer's hardware devices, including the processor, memory, hard disk, graphics card, sound card, etc. BIOS ensures that hardware devices can work properly by sending initialization signals to them.
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Check the memory: The BIOS will check the computer's memory to ensure that the memory is working properly. At this stage, the BIOS will read the data stored in the memory and verify it. If the memory fails, the BIOS will display an error message on the screen, usually a set of numeric codes.
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Check the hard drive and other storage devices: The BIOS checks the computer's hard drive and other storage devices to determine if they are available. At this stage, the BIOS reads the boot sector of the hard disk and hands over control to the boot program in the boot sector.
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Check other devices: The BIOS will also check other devices of the computer, including keyboard, mouse, monitor, sound card, etc. The BIOS ensures that these devices can work properly by sending initialization signals to them.
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Display system information: BIOS will display system information on the screen, including computer model, processor model, memory size, hard disk capacity, etc. In addition, the BIOS will also show whether the operating system is present and how to boot the operating system.
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Entering the boot program: When the BIOS self-test is completed, the BIOS will hand over control to the boot program to boot the operating system. The boot program is located in the boot sector of the hard disk. Its function is to load the core files of the operating system and transfer control to the operating system.
In short, BIOS self-test is a very important step in the computer startup process. It checks and initializes the computer's hardware devices to ensure that they can work properly. If the BIOS self-test fails, the computer will fail to start and an error message will be displayed. In this case, the user needs to check whether the computer hardware device is normal and repair it.
4. Boot device selection
Boot device selection is the third step in the computer startup process. Its main function is to determine which device the computer starts from. At this stage, the computer displays a boot menu and the user can select which device to boot the computer from, usually a hard drive or a removable device such as a CD or USB drive.
The boot device selection process includes the following steps:
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Detect available devices: During the computer startup process, the BIOS will scan all available devices, including hard drives, optical drives, USB drives, etc. When the BIOS has finished scanning, it will list the available devices in the boot menu.
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Display boot menu: After the BIOS scans available devices, the computer displays a boot menu listing the names and device types of all available devices. This menu usually appears on the screen when the computer starts, and the user can select a device using the arrow keys on the keyboard.
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Select a boot device: Users can use the arrow keys on the keyboard to select a boot device and then press the Enter key to confirm the selection. The computer will boot from the selected device and load the operating system.
When choosing a boot device, users need to pay attention to the following points:
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Choose the right device: Users should choose the right device to start the computer, usually a hard drive or a removable device. If the user selects the wrong device, the computer will fail to start and display an error message.
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Change the boot order: Users can change the boot order through BIOS settings so that the computer automatically boots from a specific device at startup. Before changing the boot sequence, users should understand their computer's hardware configuration and operating system requirements.
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Bootloader Selection: If multiple operating systems are installed in the computer, the user needs to select the correct bootloader to start the operating system. In this case, users should understand the boot program of each operating system and choose the correct boot program to start the operating system.
In short, boot device selection is a very important step in the computer startup process. It determines which device the computer will boot from and which operating system will be loaded. Users should understand the role of each device and the requirements of the operating system in order to correctly select the boot device.
5. Bootloader loading
The boot program is a very important part of the computer startup process. Its function is to load the core code of the operating system into the computer's memory and execute it after the BIOS self-test and boot device selection. This process needs to rely on the boot sector or boot record to complete.
The boot sector refers to the first sector of the hard disk, which contains the boot program code used to start the computer. When the BIOS self-test is completed, the boot program reads the boot program code from the first sector of the hard disk and loads it into the computer's memory. This process needs to rely on the hard disk controller to complete.
The boot record refers to the first sector in a removable storage device such as a CD, USB flash drive, etc. It also contains the boot program code used to start the computer. When the computer's BIOS self-test is completed, if any removable storage devices are found connected to the computer, it will check whether the first sectors of these devices contain boot records. If there is, it reads the bootloader code from this sector and loads it into memory.
During the process of loading the boot program, the BIOS will transfer control of the computer to the boot program, and the boot program will transfer control to the kernel of the operating system. The kernel of the operating system can then start booting the entire operating system. During this process, some operations such as hardware initialization and device driver loading may also be performed.
Generally speaking, the role of the boot program is to load the core code of the operating system into memory. This process is the key to starting the entire computer system.
6. Operating system loading
The loading of the operating system is the last step in the computer startup process. Its main task is to load all modules of the operating system into memory and start the initialization process of the operating system. The loading of the operating system is mainly divided into two stages: kernel loading and initialization.
During the kernel loading phase, the boot program reads the kernel code of the operating system from the hard disk into the memory. This process will involve file system-related operations, such as finding the operating system kernel file, reading files, etc. Once the kernel is successfully loaded into memory, the bootloader hands over control to the kernel and begins executing kernel code. At this point, the operating system's kernel can already begin to perform initialization operations.
During the initialization process of the operating system, the kernel initializes the hardware of the computer system and loads various modules of the operating system, such as device drivers, system services, etc. During this process, some operating system-related settings will also be performed, such as reading configuration files, setting environment variables, etc. When the initialization is completed, the operating system officially enters the running state, and the user can start using the computer system.
Generally speaking, the loading of the operating system is the last step in the computer startup process. Its main task is to load all modules of the operating system into memory and start the initialization process. During this process, the kernel initializes the computer's hardware and loads various modules so that the operating system can run normally.
7. Article summary
In general, the computer startup process is a complex and delicate process. It requires the cooperation and collaborative work of multiple hardware devices and software systems to complete the entire startup process. Each stage has a specific purpose and function.
In addition, the computer's startup sequence can also be configured through BIOS settings. Users can set different startup sequences to enable startup in different environments. For example, in some cases, users can choose to boot the operating system from an optical drive or USB device for operations such as system recovery or installation.
In short, understanding the computer startup process and startup sequence is of great significance for users to use the computer correctly and maintain the computer. By understanding the computer startup process, users can better troubleshoot computer faults, maintain the healthy operation of the computer system, and improve computer work efficiency.