A basic input/output system, BIOS, startup method, applied to a current node, wherein the current node is a master node or a slave node in a large-scale cache coherent non-uniform memory access CC-NUMA architecture system, the system comprises one master node and at least one slave node, and the method comprises: entering a first access mode, wherein a maximum access address of the current node in the first access mode is a first address, and performing the following steps in the first access mode: allocating a local memory mapped configuration MMCFG space of the current node in a space below a local access address of the current node that is the first address; performing memory initialization by accessing the local MMCFG space of the current node; and, after memory initialization is completed, performing unified memory addressing of the system, and allocating, in a global access address of the system, addresses of the MMCFG space of the current node, characterized in that an entirety or a part of the MMCFG space of the current node is a space that is above the global access address being the first address and can be accessed in a second access mode; wherein the method further comprises: allocating, in the global access address of the system, a memory mapped input/output MMIO space to the current node; and interacting with at least one other node in the system, completing node combination of the system, and forming a complete system; and entering the second access mode, wherein an address space that can be accessed by the current node in the second access mode is greater than an address space that can be accessed by the current node in the first access mode, wherein before the entering the second access mode, the method further comprises: configuring a page table in the space below the local access address of the current node that is the first address, wherein the page table points to an address space that can be accessed by the current node in the second access mode and cannot be accessed by the current node in the first access mode; and after the entering the second access mode, the method further comprises: accessing, in the global access address of the system, an address of the MMCFG space of the current node according to the page table. entering a first access mode, wherein a maximum access address of the current node in the first access mode is a first address, and performing the following steps in the first access mode: allocating a local memory mapped configuration MMCFG space of the current node in a space below a local access address of the current node that is the first address; performing memory initialization by accessing the local MMCFG space of the current node; and, after memory initialization is completed, performing unified memory addressing of the system, and allocating, in a global access address of the system, addresses of the MMCFG space of the current node, characterized in that an entirety or a part of the MMCFG space of the current node is a space that is above the global access address being the first address and can be accessed in a second access mode; wherein the method further comprises: allocating a local memory mapped configuration MMCFG space of the current node in a space below a local access address of the current node that is the first address; performing memory initialization by accessing the local MMCFG space of the current node; and, after memory initialization is completed, performing unified memory addressing of the system, and allocating, in a global access address of the system, addresses of the MMCFG space of the current node, characterized in that an entirety or a part of the MMCFG space of the current node is a space that is above the global access address being the first address and can be accessed in a second access mode; wherein the method further comprises: allocating, in the global access address of the system, a memory mapped input/output MMIO space to the current node; and interacting with at least one other node in the system, completing node combination of the system, and forming a complete system; and entering the second access mode, wherein an address space that can be accessed by the current node in the second access mode is greater than an address space that can be accessed by the current node in the first access mode, wherein before the entering the second access mode, the method further comprises: configuring a page table in the space below the local access address of the current node that is the first address, wherein the page table points to an address space that can be accessed by the current node in the second access mode and cannot be accessed by the current node in the first access mode; and after the entering the second access mode, the method further comprises: accessing, in the global access address of the system, an address of the MMCFG space of the current node according to the page table.