Primary machine and fault-tolerant system

A fault-tolerant system comprising:

• a primary machine including a primary virtual machine, the primary virtual machine including a synchronization information generator configured to generate and output synchronization information based on an instruction and a result of execution of the instruction, and a fault selector configured to determine a type of fault information generated when the instruction was executed, wherein
• the primary virtual machine changes operation based on a result of the determination of the type of fault information;
• and
• a secondary machine including a secondary virtual machine configured to execute the instruction based on the synchronization information and send a response to the primary virtual machine indicating that execution of the instruction has been completed, wherein
• the primary virtual machine executes next instruction when receiving the response from the secondary virtual machine.