What is the whole process of uefi startup?

The boot process of UEFI BIOS system

is also to boot the computer system. Since UEFI BIOS is developed according to the definition of UEFI Forum, the boot process of UEFI will be as shown in the following figure:

1. SEC stage:

The main feature of SEC stage is "cache as RAM", that is, the cache of the processor is used as memory. Because C language needs to use stack, the system memory has not been initialized at this stage. If there is no memory available, the processor cache will be used as memory, and the CPU／/chipset and motherboard will be verified in advance before the main memory is initialized.

because there is no cache at this time, the performance of the processor will become poor, so before the memory initialization is completed, the shorter the code in the SEC and PEI phases, the less this side effect will be.

2. PEI stage:

Similar to the traditional BIOS initialization stage, Pei (pre-EFI initialization) stage is used to wake up the CPU and initialize the memory. At this time, only a small part of the memory was started. At the same time, the chipset and motherboard are also initialized. The next service program will ensure that the CPU chipset is correctly initialized. At this time, the EFI driver dispatcher will load the EFI driver memory and enter the DXE phase (driver execution environment) where all the memories are initialized.

3. DXE stage:

The main function of DXE is to communicate EFI drivers and hardware. That is to say, all the memory, CPU (here refers to two or more non-core entities, that is, dual-CPU socket processors or even four-CPU socket processors), PCI, USB, SATA and Shell will be initialized.

4. BDS stage:

In this stage of BDS (boot device selection), the user can choose which detected boot device to boot from the boot manager program page.

5. TSL stage:

then enter TSL (transient system loading) stage, and the operating system will take over the boot. In addition, UEFI Shell can also be selected in BDS stage, so that the system can enter a simple command line for basic diagnosis and maintenance.