A computer system includes a memory storing an UEFI firmware and a processor. The UEFI firmware supports pre-boot initialization of a plurality of different bootloader programs, wherein the UEFI firmware has a plurality of instructions and a plurality of configuration data for different bootloader programs. The processor is operatively coupled to the memory and is used to execute the instructions of the UEFI firmware, wherein the instructions include performing the steps of: detecting type of instruction set of the processor; determining, by the processor, a bootup selection mode according to a mode selection, wherein the bootup selection mode corresponds to the detected type of instruction set, and the mode selection corresponds to the type of a bootloader program for execution after the UEFI firmware; retrieving, by the processor, a common configuration data from a plurality of configuration data of the UEFI firmware from the memory; retrieving, by the processor, a distinct configuration data from the plurality of configuration data of the UEFI firmware corresponding to the bootup selection mode from the memory, wherein the distinct configuration data comprises processor instruction sets and runtime services; generating a bootloader address corresponding to the bootup selection mode; and executing, according to the common configuration data and the distinct configuration data, the bootloader program located in a storage corresponding to the bootloader address.