1. A server system, comprising: at least one CPU; a memory for storing data and a program; and an interface for exchanging data with the outside, wherein: the CPU executes the program stored in the memory to execute a virtual machine monitor for operating at least one virtual computer in which an operating system operates; and the virtual machine monitor includes: an emulation module for emulating an operation based on an operation code for executing the operation of hardware of the server system when the operation of the hardware of the server system is requested by one of the operating system and an application operated in the operating system; an exception event handler module for calling the emulation module when an exception event is generated by the CPU through detection of the operation of the hardware of the server system; a code management module for managing a promotion code used for emulating the operation of the hardware of the server system by switching an operation mode of the CPU to call the emulation module; a frequency judgment module for judging whether a frequency of the operation of the hardware of the server system is high based on a result of comparison with predetermined judgment conditions; and a switching module for determining whether to call the emulation module by one of the exception event handler module and by executing the promotion code based on the judged frequency.